     [file version.txi not included]

This file documents SLIB, the portable Scheme library.

Copyright (C) 1993 Todd R. Eigenschink

Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002 Aubrey Jaffer

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the author.

SLIB is a portable library for the programming language Scheme.  It provides a platform independent framework for using packages of Scheme procedures and syntax.  As distributed, SLIB contains useful packages for all Scheme implementations.  Its catalog can be transparently extended to accomodate packages specific to a site, implementation, user, or directory.

The Library System
******************

Feature
=======

SLIB denotes features by symbols.  SLIB maintains a list of features supported by the Scheme session.  The set of features provided by a session may change over time.  Some features are properties of the Scheme implementation being used.  The following features detail what sort of numbers are available from an implementation.

  * 'inexact

  * 'rational

  * 'real

  * 'complex

  * 'bignum

Other features correspond to the presence of sets of Scheme procedures or syntax (macros).

 -- Function: provided? feature
     Returns #t if FEATURE is supported by the current Scheme session.

 -- Procedure: provide feature
     Informs SLIB that FEATURE is supported.  Henceforth (provided? FEATURE) will return #t.

     (provided? 'foo)    => #f
     (provide 'foo)
     (provided? 'foo)    => #t

Requesting Features
===================

SLIB creates and maintains a catalog mapping features to locations of files introducing procedures and syntax denoted by those features.

At the beginning of each section of this manual, there is a line like (require 'FEATURE). The Scheme files comprising SLIB are cataloged so that these feature names map to the corresponding files.

SLIB provides a form, require, which loads the files providing the requested feature.

 -- Procedure: require feature

       * If (provided? FEATURE) is true, then require just returns an unspecified value.

       * Otherwise, if FEATURE is found in the catalog, then the corresponding files will be loaded and an unspecified value returned.

          Subsequently (provided? FEATURE) will return #t.

       * Otherwise (FEATURE not found in the catalog), an error is signaled.

The catalog can also be queried using require:feature->path.

 -- Function: require:feature->path feature

       * If FEATURE is already provided, then returns #t.

       * Otherwise, if FEATURE is in the catalog, the path or list of paths associated with FEATURE is returned.

       * Otherwise, returns #f.

Library Catalogs
================

At the start of a session no catalog is present, but is created with the first catalog inquiry (such as (require 'random)).  Several sources of catalog information are combined to produce the catalog:

  * standard SLIB packages.

  * additional packages of interest to this site.

  * packages specifically for the variety of Scheme which this session is running.

  * packages this user wants to always have available.  This catalog is the file homecat in the user's HOME directory.

  * packages germane to working in this (current working) directory.  This catalog is the file usercat in the directory to which it applies. One would typically cd to this directory before starting the Scheme session.

Catalog files consist of one or more association lists. In the circumstance where a feature symbol appears in more than one list, the latter list's association is retrieved.  Here are the supported formats for elements of catalog lists:

(FEATURE . <symbol>)
     Redirects to the feature named <symbol>.

(FEATURE . "<path>")
     Loads file <path>.

(FEATURE source "<path>")
     slib:loads the Scheme source file <path>.

(FEATURE compiled "<path>" ...)
     slib:load-compileds the files <path> ....

(FEATURE aggregate <symbol> ...)
     require:requires the features <symbol> ....

The various macro styles first require the named macro package, then just load <path> or load-and-macro-expand <path> as appropriate for the implementation.

(FEATURE defmacro "<path>")
     defmacro:loads the Scheme source file <path>.

(FEATURE macro-by-example "<path>")
     defmacro:loads the Scheme source file <path>.

(FEATURE macro "<path>")
     macro:loads the Scheme source file <path>.

(FEATURE macros-that-work "<path>")
     macro:loads the Scheme source file <path>.

(FEATURE syntax-case "<path>")
     macro:loads the Scheme source file <path>.

(FEATURE syntactic-closures "<path>")
     macro:loads the Scheme source file <path>.

Here is an example of a usercat catalog.  A Program in this directory can invoke the run feature with (require 'run).

     ;;; "usercat": SLIB catalog additions for SIMSYNCH.     -*-scheme-*-

     (
      (simsynch      . "../synch/simsynch.scm")
      (run           . "../synch/run.scm")
      (schlep        . "schlep.scm")
     )

Catalog Compilation
===================

SLIB combines the catalog information which doesn't vary per user into the file slibcat in the implementation-vicinity.  Therefore slibcat needs change only when new software is installed or compiled.  Because the actual pathnames of files can differ from installation to installation, SLIB builds a separate catalog for each implementation it is used with.

The definition of *SLIB-VERSION* in SLIB file require.scm is checked against the catalog association of *SLIB-VERSION* to ascertain when versions have changed.  I recommend that the definition of *SLIB-VERSION* be changed whenever the library is changed.  If multiple implementations of Scheme use SLIB, remember that recompiling one slibcat will fix only that implementation's catalog.

The compilation scripts of Scheme implementations which work with SLIB can automatically trigger catalog compilation by deleting slibcat or by invoking a special form of require:

 -- Procedure: require 'new-catalog
     This will load mklibcat, which compiles and writes a new slibcat.

Another special form of require erases SLIB's catalog, forcing it to be reloaded the next time the catalog is queried.

 -- Procedure: require #f
     Removes SLIB's catalog information.  This should be done before saving an executable image so that, when restored, its catalog will be loaded afresh.

Each file in the table below is descibed in terms of its file-system independent vicinity (see Vicinity).  The entries of a catalog in the table override those of catalogs above it in the table.

implementation-vicinity slibcat
     This file contains the associations for the packages comprising SLIB, the implcat and the sitecats.  The associations in the other catalogs override those of the standard catalog.

library-vicinity mklibcat.scm
     creates slibcat.

library-vicinity sitecat
     This file contains the associations specific to an SLIB installation.

implementation-vicinity implcat
     This file contains the associations specific to an implementation of Scheme.  Different implementations of Scheme should have different implementation-vicinity.

implementation-vicinity mkimpcat.scm
     if present, creates implcat.

implementation-vicinity sitecat
     This file contains the associations specific to a Scheme implementation installation.

home-vicinity homecat
     This file contains the associations specific to an SLIB user.

user-vicinity usercat
     This file contains associations effecting only those sessions whose working directory is user-vicinity.

Built-in Support
================

The procedures described in these sections are supported by all implementations as part of the *.init files or by require.scm.

Require
-------

 -- Variable: *features*
     Is a list of symbols denoting features supported in this implementation. *FEATURES* can grow as modules are required. *FEATURES* must be defined by all implementations (see Porting).

     Here are features which SLIB (require.scm) adds to *FEATURES* when appropriate.

       * 'inexact

       * 'rational

       * 'real

       * 'complex

       * 'bignum

     For each item, (provided? 'FEATURE) will return #t if that feature is available, and #f if not.

 -- Variable: *modules*
     Is a list of pathnames denoting files which have been loaded.

 -- Variable: *catalog*
     Is an association list of features (symbols) and pathnames which will supply those features.  The pathname can be either a string or a pair. If pathname is a pair then the first element should be a macro feature symbol, source, or compiled.  The cdr of the pathname should be either a string or a list.

In the following functions if the argument FEATURE is not a symbol it is assumed to be a pathname.

 -- Function: provided? feature
     Returns #t if FEATURE is a member of *features* or *modules* or if FEATURE is supported by a file already loaded and #f otherwise.

 -- Procedure: require feature
     FEATURE is a symbol.  If (provided? FEATURE) is true require returns.  Otherwise, if (assq FEATURE *catalog*) is not #f, the associated files will be loaded and (provided? FEATURE) will henceforth return #t.  An unspecified value is returned.  If FEATURE is not found in *catalog*, then an error is signaled.

 -- Procedure: require pathname
     PATHNAME is a string.  If PATHNAME has not already been given as an argument to require, PATHNAME is loaded.  An unspecified value is returned.

 -- Procedure: provide feature
     Assures that FEATURE is contained in *features* if FEATURE is a symbol and *modules* otherwise.

 -- Function: require:feature->path feature
     Returns #t if FEATURE is a member of *features* or *modules* or if FEATURE is supported by a file already loaded.  Returns a path if one was found in *catalog* under the feature name, and #f otherwise.  The path can either be a string suitable as an argument to load or a pair as described above for *catalog*.

Vicinity
--------

A vicinity is a descriptor for a place in the file system.  Vicinities hide from the programmer the concepts of host, volume, directory, and version.  Vicinities express only the concept of a file environment where a file name can be resolved to a file in a system independent manner.  Vicinities can even be used on flat file systems (which have no directory structure) by having the vicinity express constraints on the file name.  On most systems a vicinity would be a string.  All of these procedures are file system dependent.

These procedures are provided by all implementations.

 -- Function: make-vicinity dirpath
     Returns DIRPATH as a vicinity for use as first argument to in-vicinity.

 -- Function: pathname->vicinity path
     Returns the vicinity containing PATH.

          (pathname->vicinity "/usr/local/lib/scm/Link.scm")
                              => "/usr/local/lib/scm/"

 -- Function: program-vicinity
     Returns the vicinity of the currently loading Scheme code.  For an interpreter this would be the directory containing source code.  For a compiled system (with multiple files) this would be the directory where the object or executable files are.  If no file is currently loading it the result is undefined.  Warning: program-vicinity can return incorrect values if your program escapes back into a load.

 -- Function: library-vicinity
     Returns the vicinity of the shared Scheme library.

 -- Function: implementation-vicinity
     Returns the vicinity of the underlying Scheme implementation.  This vicinity will likely contain startup code and messages and a compiler.

 -- Function: user-vicinity
     Returns the vicinity of the current directory of the user.  On most systems this is "" (the empty string).

 -- Function: home-vicinity
     Returns the vicinity of the user's HOME directory, the directory which typically contains files which customize a computer environment for a user.  If scheme is running without a user (eg. a daemon) or if this concept is meaningless for the platform, then home-vicinity returns #f.

 -- Function: in-vicinity vicinity filename
     Returns a filename suitable for use by slib:load, slib:load-source, slib:load-compiled, open-input-file, open-output-file, etc.  The returned filename is FILENAME in VICINITY.  in-vicinity should allow FILENAME to override VICINITY when FILENAME is an absolute pathname and VICINITY is equal to the value of (user-vicinity).  The behavior of in-vicinity when FILENAME is absolute and VICINITY is not equal to the value of (user-vicinity) is unspecified.  For most systems in-vicinity can be string-append.

 -- Function: sub-vicinity vicinity name
     Returns the vicinity of VICINITY restricted to NAME.  This is used for large systems where names of files in subsystems could conflict.  On systems with directory structure sub-vicinity will return a pathname of the subdirectory NAME of VICINITY.

Configuration
-------------

These constants and procedures describe characteristics of the Scheme and underlying operating system.  They are provided by all implementations.

 -- Constant: char-code-limit
     An integer 1 larger that the largest value which can be returned by char->integer.

 -- Constant: most-positive-fixnum
     In implementations which support integers of practically unlimited size, MOST-POSITIVE-FIXNUM is a large exact integer within the range of exact integers that may result from computing the length of a list, vector, or string.

     In implementations which do not support integers of practically unlimited size, MOST-POSITIVE-FIXNUM is the largest exact integer that may result from computing the length of a list, vector, or string.

 -- Constant: slib:tab
     The tab character.

 -- Constant: slib:form-feed
     The form-feed character.

 -- Function: software-type
     Returns a symbol denoting the generic operating system type.  For instance, unix, vms, macos, amiga, or ms-dos.

 -- Function: slib:report-version
     Displays the versions of SLIB and the underlying Scheme implementation and the name of the operating system.  An unspecified value is returned.

          (slib:report-version) => slib "SLIBVERSION" on scm "5b1" on unix

 -- Function: slib:report
     Displays the information of (slib:report-version) followed by almost all the information neccessary for submitting a problem report. An unspecified value is returned.

 -- Function: slib:report #t
     provides a more verbose listing.

 -- Function: slib:report filename
     Writes the report to file filename.

          (slib:report)
          =>
          slib "SLIBVERSION" on scm "5b1" on unix
          (implementation-vicinity) is "/home/jaffer/scm/"
          (library-vicinity) is "/home/jaffer/slib/"
          (scheme-file-suffix) is ".scm"
          loaded *features* :
                  trace alist qp sort
                  common-list-functions macro values getopt
                  compiled
          implementation *features* :
                  bignum complex real rational
                  inexact vicinity ed getenv
                  tmpnam abort transcript with-file
                  ieee-p1178 rev4-report rev4-optional-procedures hash
                  object-hash delay eval dynamic-wind
                  multiarg-apply multiarg/and- logical defmacro
                  string-port source current-time record
                  rev3-procedures rev2-procedures sun-dl string-case
                  array dump char-ready? full-continuation
                  system
          implementation *catalog* :
                  (i/o-extensions compiled "/home/jaffer/scm/ioext.so")
                  ...

Input/Output
------------

These procedures are provided by all implementations.

 -- Function: file-exists? filename
     Returns #t if the specified file exists.  Otherwise, returns #f.  If the underlying implementation does not support this feature then #f is always returned.

 -- Function: delete-file filename
     Deletes the file specified by FILENAME.  If FILENAME can not be deleted, #f is returned.  Otherwise, #t is returned.

 -- Function: open-file filename modes
     FILENAME should be a string naming a file.  open-file returns a port depending on the symbol MODES:

     r
          an input port capable of delivering characters from the file.

     rb
          a binary input port capable of delivering characters from the file.

     w
          an output port capable of writing characters to a new file by that name.

     wb
          a binary output port capable of writing characters to a new file by that name.

     If an implementation does not distinguish between binary and non-binary files, then it must treat rb as r and wb as w.

     If the file cannot be opened, either #f is returned or an error is signalled.  For output, if a file with the given name already exists, the effect is unspecified.

 -- Function: port? obj
     Returns #t if OBJ is an input or output port, otherwise returns #f.

 -- Procedure: close-port port
     Closes the file associated with PORT, rendering the PORT incapable of delivering or accepting characters.

     close-file has no effect if the file has already been closed. The value returned is unspecified.

 -- Function: call-with-open-ports proc ports ...
 -- Function: call-with-open-ports ports ... proc
     PROC should be a procedure that accepts as many arguments as there are PORTS passed to call-with-open-ports. call-with-open-ports calls PROC with PORTS .... If PROC returns, then the ports are closed automatically and the value yielded by the PROC is returned.  If PROC does not return, then the ports will not be closed automatically unless it is possible to prove that the ports will never again be used for a read or write operation.

 -- Function: tmpnam
     Returns a pathname for a file which will likely not be used by any other process.  Successive calls to (tmpnam) will return different pathnames.

 -- Function: current-error-port
     Returns the current port to which diagnostic and error output is directed.

 -- Procedure: force-output
 -- Procedure: force-output port
     Forces any pending output on PORT to be delivered to the output device and returns an unspecified value.  The PORT argument may be omitted, in which case it defaults to the value returned by (current-output-port).

 -- Function: output-port-width
 -- Function: output-port-width port

     Returns the width of PORT, which defaults to (current-output-port) if absent.  If the width cannot be determined 79 is returned.

 -- Function: output-port-height
 -- Function: output-port-height port

     Returns the height of PORT, which defaults to (current-output-port) if absent.  If the height cannot be determined 24 is returned.

System
------

These procedures are provided by all implementations.

 -- Procedure: slib:load-source name
     Loads a file of Scheme source code from NAME with the default filename extension used in SLIB.  For instance if the filename extension used in SLIB is .scm then (slib:load-source "foo") will load from file foo.scm.

 -- Procedure: slib:load-compiled name
     On implementations which support separtely loadable compiled modules, loads a file of compiled code from NAME with the implementation's filename extension for compiled code appended.

 -- Procedure: slib:load name
     Loads a file of Scheme source or compiled code from NAME with the appropriate suffixes appended.  If both source and compiled code are present with the appropriate names then the implementation will load just one.  It is up to the implementation to choose which one will be loaded.

     If an implementation does not support compiled code then slib:load will be identical to slib:load-source.

 -- Procedure: slib:eval obj
     eval returns the value of OBJ evaluated in the current top level environment.  Eval provides a more general evaluation facility.

 -- Procedure: slib:eval-load filename eval
     FILENAME should be a string.  If filename names an existing file, the Scheme source code expressions and definitions are read from the file and EVAL called with them sequentially.  The slib:eval-load procedure does not affect the values returned by current-input-port and current-output-port.

 -- Procedure: slib:warn arg1 arg2 ...
     Outputs a warning message containing the arguments.

 -- Procedure: slib:error arg1 arg2 ...
     Outputs an error message containing the arguments, aborts evaluation of the current form and responds in a system dependent way to the error. Typical responses are to abort the program or to enter a read-eval-print loop.

 -- Procedure: slib:exit n
 -- Procedure: slib:exit
     Exits from the Scheme session returning status N to the system. If N is omitted or #t, a success status is returned to the system (if possible).  If N is #f a failure is returned to the system (if possible).  If N is an integer, then N is returned to the system (if possible).  If the Scheme session cannot exit an unspecified value is returned from slib:exit.

 -- Function: browse-url url
     Web browsers have become so ubiquitous that programming languagues should support a uniform interface to them.

     If a netscape browser is running, browse-url causes the browser to display the page specified by string URL and returns #t.

     If the browser is not running, browse-url starts a browser displaying the argument URL.  If the browser starts as a background job, browse-url returns #t immediately; if the browser starts as a foreground job, then browse-url returns #t when the browser exits; otherwise it returns #f.

Miscellany
----------

These procedures are provided by all implementations.

 -- Function: identity x
     IDENTITY returns its argument.

     Example:

          (identity 3)
             => 3
          (identity '(foo bar))
             => (foo bar)
          (map identity LST)
             == (copy-list LST)

Mutual Exclusion
................

An exchanger is a procedure of one argument regulating mutually exclusive access to a resource.  When a exchanger is called, its current content is returned, while being replaced by its argument in an atomic operation.

 -- Function: make-exchanger obj

     Returns a new exchanger with the argument OBJ as its initial content.

          (define queue (make-exchanger (list a)))

     A queue implemented as an exchanger holding a list can be protected from reentrant execution thus:

          (define (pop queue)
            (let ((lst #f))
              (dynamic-wind
                  (lambda () (set! lst (queue #f)))
                  (lambda () (and lst (not (null? lst))
                                  (let ((ret (car lst)))
                                    (set! lst (cdr lst))
                                    ret)))
                  (lambda () (and lst (queue lst))))))

          (pop queue)         => a

          (pop queue)         => #f

Legacy
......

The following procedures were present in Scheme until R4RS (see Language changes (Revised(4) Scheme)). They are provided by all SLIB implementations.

 -- Constant: t
     Derfined as #t.

 -- Constant: nil
     Defined as #f.

 -- Function: last-pair l
     Returns the last pair in the list L.  Example:

          (last-pair (cons 1 2))
             => (1 . 2)
          (last-pair '(1 2))
             => (2)
              == (cons 2 '())

About this manual
=================

  * Entries that are labeled as Functions are called for their return values.  Entries that are labeled as Procedures are called primarily for their side effects.

  * Examples in this text were produced using the scm Scheme implementation.

  * At the beginning of each section, there is a line that looks like (require 'feature).  Include this line in your code prior to using the package.

Scheme Syntax Extension Packages
********************************

Defmacro
========

Defmacros are supported by all implementations.

 -- Function: gentemp
     Returns a new (interned) symbol each time it is called.  The symbol names are implementation-dependent

          (gentemp) => scm:G0
          (gentemp) => scm:G1

 -- Function: defmacro:eval e
     Returns the slib:eval of expanding all defmacros in scheme expression E.

 -- Function: defmacro:load filename
     FILENAME should be a string.  If filename names an existing file, the defmacro:load procedure reads Scheme source code expressions and definitions from the file and evaluates them sequentially.  These source code expressions and definitions may contain defmacro definitions.  The macro:load procedure does not affect the values returned by current-input-port and current-output-port.

 -- Function: defmacro? sym
     Returns #t if SYM has been defined by defmacro, #f otherwise.

 -- Function: macroexpand-1 form
 -- Function: macroexpand form
     If FORM is a macro call, macroexpand-1 will expand the macro call once and return it.  A FORM is considered to be a macro call only if it is a cons whose car is a symbol for which a defmacro has been defined.

     macroexpand is similar to macroexpand-1, but repeatedly expands FORM until it is no longer a macro call.

 -- Macro: defmacro name lambda-list form ...
     When encountered by defmacro:eval, defmacro:macroexpand*, or defmacro:load defines a new macro which will henceforth be expanded when encountered by defmacro:eval, defmacro:macroexpand*, or defmacro:load.

Defmacroexpand
--------------

(require 'defmacroexpand)

 -- Function: defmacro:expand* e
     Returns the result of expanding all defmacros in scheme expression E.

R4RS Macros
===========

(require 'macro) is the appropriate call if you want R4RS high-level macros but don't care about the low level implementation.  If an SLIB R4RS macro implementation is already loaded it will be used. Otherwise, one of the R4RS macros implemetations is loaded.

The SLIB R4RS macro implementations support the following uniform interface:

 -- Function: macro:expand sexpression
     Takes an R4RS expression, macro-expands it, and returns the result of the macro expansion.

 -- Function: macro:eval sexpression
     Takes an R4RS expression, macro-expands it, evals the result of the macro expansion, and returns the result of the evaluation.

 -- Procedure: macro:load filename
     FILENAME should be a string.  If filename names an existing file, the macro:load procedure reads Scheme source code expressions and definitions from the file and evaluates them sequentially.  These source code expressions and definitions may contain macro definitions.  The macro:load procedure does not affect the values returned by current-input-port and current-output-port.

Macro by Example
================

(require 'macro-by-example)

A vanilla implementation of Macro by Example (Eugene Kohlbecker, R4RS) by Dorai Sitaram, (dorai @ cs.rice.edu) using defmacro.

  * generating hygienic global define-syntax Macro-by-Example macros cheaply.

  * can define macros which use ....

  * needn't worry about a lexical variable in a macro definition clashing with a variable from the macro use context

  * don't suffer the overhead of redefining the repl if defmacro natively supported (most implementations)

Caveat
------

These macros are not referentially transparent (see Macros (Revised(4) Scheme)).  Lexically scoped macros (i.e., let-syntax and letrec-syntax) are not supported.  In any case, the problem of referential transparency gains poignancy only when let-syntax and letrec-syntax are used.  So you will not be courting large-scale disaster unless you're using system-function names as local variables with unintuitive bindings that the macro can't use.  However, if you must have the full r4rs macro functionality, look to the more featureful (but also more expensive) versions of syntax-rules available in slib Macros That Work, Syntactic Closures, and Syntax-Case Macros.

 -- Macro: define-syntax keyword transformer-spec
     The KEYWORD is an identifier, and the TRANSFORMER-SPEC should be an instance of syntax-rules.

     The top-level syntactic environment is extended by binding the KEYWORD to the specified transformer.

          (define-syntax let*
            (syntax-rules ()
              ((let* () body1 body2 ...)
               (let () body1 body2 ...))
              ((let* ((name1 val1) (name2 val2) ...)
                 body1 body2 ...)
               (let ((name1 val1))
                 (let* (( name2 val2) ...)
                   body1 body2 ...)))))

 -- Macro: syntax-rules literals syntax-rule ...
     LITERALS is a list of identifiers, and each SYNTAX-RULE should be of the form

     (PATTERN TEMPLATE)

     where the PATTERN and  TEMPLATE are as in the grammar above.

     An instance of syntax-rules produces a new macro transformer by specifying a sequence of hygienic rewrite rules.  A use of a macro whose keyword is associated with a transformer specified by syntax-rules is matched against the patterns contained in the SYNTAX-RULEs, beginning with the leftmost SYNTAX-RULE. When a match is found, the macro use is trancribed hygienically according to the template.

     Each pattern begins with the keyword for the macro.  This keyword is not involved in the matching and is not considered a pattern variable or literal identifier.

Macros That Work
================

(require 'macros-that-work)

Macros That Work differs from the other R4RS macro implementations in that it does not expand derived expression types to primitive expression types.

 -- Function: macro:expand expression
 -- Function: macwork:expand expression
     Takes an R4RS expression, macro-expands it, and returns the result of the macro expansion.

 -- Function: macro:eval expression
 -- Function: macwork:eval expression
     macro:eval returns the value of EXPRESSION in the current top level environment.  EXPRESSION can contain macro definitions. Side effects of EXPRESSION will affect the top level environment.

 -- Procedure: macro:load filename
 -- Procedure: macwork:load filename
     FILENAME should be a string.  If filename names an existing file, the macro:load procedure reads Scheme source code expressions and definitions from the file and evaluates them sequentially.  These source code expressions and definitions may contain macro definitions.  The macro:load procedure does not affect the values returned by current-input-port and current-output-port.

References:

The Revised^4 Report on the Algorithmic Language Scheme Clinger and Rees [editors].  To appear in LISP Pointers.  Also available as a technical report from the University of Oregon, MIT AI Lab, and Cornell.

Macros That Work.  Clinger and Rees.  POPL '91.

The supported syntax differs from the R4RS in that vectors are allowed as patterns and as templates and are not allowed as pattern or template data.

     transformer spec  ==>  (syntax-rules literals rules)

     rules  ==>  ()
              |  (rule . rules)

     rule  ==>  (pattern template)

     pattern  ==>  pattern_var      ; a symbol not in literals
                |  symbol           ; a symbol in literals
                |  ()
                |  (pattern . pattern)
                |  (ellipsis_pattern)
                |  #(pattern*)                     ; extends R4RS
                |  #(pattern* ellipsis_pattern)    ; extends R4RS
                |  pattern_datum

     template  ==>  pattern_var
                 |  symbol
                 |  ()
                 |  (template2 . template2)
                 |  #(template*)                   ; extends R4RS
                 |  pattern_datum

     template2  ==>  template
                  |  ellipsis_template

     pattern_datum  ==>  string                    ; no vector
                      |  character
                      |  boolean
                      |  number

     ellipsis_pattern  ==> pattern ...

     ellipsis_template  ==>  template ...

     pattern_var  ==>  symbol   ; not in literals

     literals  ==>  ()
                 |  (symbol . literals)

Definitions
-----------

Scope of an ellipsis
     Within a pattern or template, the scope of an ellipsis (...) is the pattern or template that appears to its left.

Rank of a pattern variable
     The rank of a pattern variable is the number of ellipses within whose scope it appears in the pattern.

Rank of a subtemplate
     The rank of a subtemplate is the number of ellipses within whose scope it appears in the template.

Template rank of an occurrence of a pattern variable
     The template rank of an occurrence of a pattern variable within a template is the rank of that occurrence, viewed as a subtemplate.

Variables bound by a pattern
     The variables bound by a pattern are the pattern variables that appear within it.

Referenced variables of a subtemplate
     The referenced variables of a subtemplate are the pattern variables that appear within it.

Variables opened by an ellipsis template
     The variables opened by an ellipsis template are the referenced pattern variables whose rank is greater than the rank of the ellipsis template.

Restrictions
------------

No pattern variable appears more than once within a pattern.

For every occurrence of a pattern variable within a template, the template rank of the occurrence must be greater than or equal to the pattern variable's rank.

Every ellipsis template must open at least one variable.

For every ellipsis template, the variables opened by an ellipsis template must all be bound to sequences of the same length.

The compiled form of a RULE is

     rule  ==>  (pattern template inserted)

     pattern  ==>  pattern_var
                |  symbol
                |  ()
                |  (pattern . pattern)
                |  ellipsis_pattern
                |  #(pattern)
                |  pattern_datum

     template  ==>  pattern_var
                 |  symbol
                 |  ()
                 |  (template2 . template2)
                 |  #(pattern)
                 |  pattern_datum

     template2  ==>  template
                  |  ellipsis_template

     pattern_datum  ==>  string
                      |  character
                      |  boolean
                      |  number

     pattern_var  ==>  #(V symbol rank)

     ellipsis_pattern  ==>  #(E pattern pattern_vars)

     ellipsis_template  ==>  #(E template pattern_vars)

     inserted  ==>  ()
                 |  (symbol . inserted)

     pattern_vars  ==>  ()
                     |  (pattern_var . pattern_vars)

     rank  ==>  exact non-negative integer

where V and E are unforgeable values.

The pattern variables associated with an ellipsis pattern are the variables bound by the pattern, and the pattern variables associated with an ellipsis template are the variables opened by the ellipsis template.

If the template contains a big chunk that contains no pattern variables or inserted identifiers, then the big chunk will be copied unnecessarily.  That shouldn't matter very often.

Syntactic Closures
==================

(require 'syntactic-closures)

 -- Function: macro:expand expression
 -- Function: synclo:expand expression
     Returns scheme code with the macros and derived expression types of EXPRESSION expanded to primitive expression types.

 -- Function: macro:eval expression
 -- Function: synclo:eval expression
     macro:eval returns the value of EXPRESSION in the current top level environment.  EXPRESSION can contain macro definitions. Side effects of EXPRESSION will affect the top level environment.

 -- Procedure: macro:load filename
 -- Procedure: synclo:load filename
     FILENAME should be a string.  If filename names an existing file, the macro:load procedure reads Scheme source code expressions and definitions from the file and evaluates them sequentially.  These source code expressions and definitions may contain macro definitions. The macro:load procedure does not affect the values returned by current-input-port and current-output-port.

Syntactic Closure Macro Facility
--------------------------------

A Syntactic Closures Macro Facility
by Chris Hanson
9 November 1991

This document describes syntactic closures, a low-level macro facility for the Scheme programming language.  The facility is an alternative to the low-level macro facility described in the Revised^4 Report on Scheme. This document is an addendum to that report.

The syntactic closures facility extends the BNF rule for TRANSFORMER SPEC to allow a new keyword that introduces a low-level macro transformer:

     TRANSFORMER SPEC := (transformer EXPRESSION)

Additionally, the following procedures are added:

     make-syntactic-closure
     capture-syntactic-environment
     identifier?
     identifier=?

The description of the facility is divided into three parts.  The first part defines basic terminology.  The second part describes how macro transformers are defined.  The third part describes the use of identifiers, which extend the syntactic closure mechanism to be compatible with syntax-rules.

Terminology
...........

This section defines the concepts and data types used by the syntactic closures facility.

  * Forms are the syntactic entities out of which programs are recursively constructed.  A form is any expression, any definition, any syntactic keyword, or any syntactic closure.  The variable name that appears in a set! special form is also a form.  Examples of forms:

          17
          #t
          car
          (+ x 4)
          (lambda (x) x)
          (define pi 3.14159)
          if
          define

  * An alias is an alternate name for a given symbol.  It can appear anywhere in a form that the symbol could be used, and when quoted it is replaced by the symbol; however, it does not satisfy the predicate symbol?.  Macro transformers rarely distinguish symbols from aliases, referring to both as identifiers.

  * A syntactic environment maps identifiers to their meanings.  More precisely, it determines whether an identifier is a syntactic keyword or a variable.  If it is a keyword, the meaning is an interpretation for the form in which that keyword appears.  If it is a variable, the meaning identifies which binding of that variable is referenced.  In short, syntactic environments contain all of the contextual information necessary for interpreting the meaning of a particular form.

  * A syntactic closure consists of a form, a syntactic environment, and a list of identifiers.  All identifiers in the form take their meaning from the syntactic environment, except those in the given list.  The identifiers in the list are to have their meanings determined later.  A syntactic closure may be used in any context in which its form could have been used.  Since a syntactic closure is also a form, it may not be used in contexts where a form would be illegal. For example, a form may not appear as a clause in the cond special form. A syntactic closure appearing in a quoted structure is replaced by its form.

Transformer Definition
......................

This section describes the transformer special form and the procedures make-syntactic-closure and capture-syntactic-environment.

 -- Syntax: transformer expression

     Syntax: It is an error if this syntax occurs except as a TRANSFORMER SPEC.

     Semantics: The EXPRESSION is evaluated in the standard transformer environment to yield a macro transformer as described below.  This macro transformer is bound to a macro keyword by the special form in which the transformer expression appears (for example, let-syntax).

     A macro transformer is a procedure that takes two arguments, a form and a syntactic environment, and returns a new form.  The first argument, the input form, is the form in which the macro keyword occurred.  The second argument, the usage environment, is the syntactic environment in which the input form occurred.  The result of the transformer, the output form, is automatically closed in the transformer environment, which is the syntactic environment in which the transformer expression occurred.

     For example, here is a definition of a push macro using syntax-rules:

          (define-syntax  push
            (syntax-rules ()
              ((push item list)
               (set! list (cons item list)))))

     Here is an equivalent definition using transformer:

          (define-syntax push
            (transformer
             (lambda (exp env)
               (let ((item
                      (make-syntactic-closure env '() (cadr exp)))
                     (list
                      (make-syntactic-closure env '() (caddr exp))))
                 `(set! ,list (cons ,item ,list))))))

     In this example, the identifiers set! and cons are closed in the transformer environment, and thus will not be affected by the meanings of those identifiers in the usage environment env.

     Some macros may be non-hygienic by design.  For example, the following defines a loop macro that implicitly binds exit to an escape procedure.  The binding of exit is intended to capture free references to exit in the body of the loop, so exit must be left free when the body is closed:

          (define-syntax loop
            (transformer
             (lambda (exp env)
               (let ((body (cdr exp)))
                 `(call-with-current-continuation
                   (lambda (exit)
                     (let f ()
                       ,@(map (lambda  (exp)
                                 (make-syntactic-closure env '(exit)
                                                         exp))
                               body)
                       (f))))))))

     To assign meanings to the identifiers in a form, use make-syntactic-closure to close the form in a syntactic environment.

 -- Function: make-syntactic-closure environment free-names form

     ENVIRONMENT must be a syntactic environment, FREE-NAMES must be a list of identifiers, and FORM must be a form. make-syntactic-closure constructs and returns a syntactic closure of FORM in ENVIRONMENT, which can be used anywhere that FORM could have been used.  All the identifiers used in FORM, except those explicitly excepted by FREE-NAMES, obtain their meanings from ENVIRONMENT.

     Here is an example where FREE-NAMES is something other than the empty list.  It is instructive to compare the use of FREE-NAMES in this example with its use in the loop example above: the examples are similar except for the source of the identifier being left free.

          (define-syntax let1
            (transformer
             (lambda (exp env)
               (let ((id (cadr exp))
                     (init (caddr exp))
                     (exp (cadddr exp)))
                 `((lambda (,id)
                     ,(make-syntactic-closure env (list id) exp))
                   ,(make-syntactic-closure env '() init))))))

     let1 is a simplified version of let that only binds a single identifier, and whose body consists of a single expression.  When the body expression is syntactically closed in its original syntactic environment, the identifier that is to be bound by let1 must be left free, so that it can be properly captured by the lambda in the output form.

     To obtain a syntactic environment other than the usage environment, use capture-syntactic-environment.

 -- Function: capture-syntactic-environment procedure

     capture-syntactic-environment returns a form that will, when transformed, call PROCEDURE on the current syntactic environment. PROCEDURE should compute and return a new form to be transformed, in that same syntactic environment, in place of the form.

     An example will make this clear.  Suppose we wanted to define a simple loop-until keyword equivalent to

          (define-syntax loop-until
            (syntax-rules ()
              ((loop-until id init test return step)
               (letrec ((loop
                         (lambda (id)
                           (if test return (loop step)))))
                 (loop init)))))

     The following attempt at defining loop-until has a subtle bug:

          (define-syntax loop-until
            (transformer
             (lambda (exp env)
               (let ((id (cadr exp))
                     (init (caddr exp))
                     (test (cadddr exp))
                     (return (cadddr (cdr exp)))
                     (step (cadddr (cddr exp)))
                     (close
                      (lambda (exp free)
                        (make-syntactic-closure env free exp))))
                 `(letrec ((loop
                            (lambda (,id)
                              (if ,(close test (list id))
                                  ,(close return (list id))
                                  (loop ,(close step (list id)))))))
                    (loop ,(close init '())))))))

     This definition appears to take all of the proper precautions to prevent unintended captures.  It carefully closes the subexpressions in their original syntactic environment and it leaves the id identifier free in the test, return, and step expressions, so that it will be captured by the binding introduced by the lambda expression.  Unfortunately it uses the identifiers if and loop within that lambda expression, so if the user of loop-until just happens to use, say, if for the identifier, it will be inadvertently captured.

     The syntactic environment that if and loop want to be exposed to is the one just outside the lambda expression: before the user's identifier is added to the syntactic environment, but after the identifier loop has been added. capture-syntactic-environment captures exactly that environment as follows:

          (define-syntax loop-until
            (transformer
             (lambda (exp env)
               (let ((id (cadr exp))
                     (init (caddr exp))
                     (test (cadddr exp))
                     (return (cadddr (cdr exp)))
                     (step (cadddr (cddr exp)))
                     (close
                      (lambda (exp free)
                        (make-syntactic-closure env free exp))))
                 `(letrec ((loop
                            ,(capture-syntactic-environment
                              (lambda (env)
                                `(lambda (,id)
                                   (,(make-syntactic-closure env '() `if)
                                    ,(close test (list id))
                                    ,(close return (list id))
                                    (,(make-syntactic-closure env '()
                                                              `loop)
                                     ,(close step (list id)))))))))
                    (loop ,(close init '())))))))

     In this case, having captured the desired syntactic environment, it is convenient to construct syntactic closures of the identifiers if and the loop and use them in the body of the lambda.

     A common use of capture-syntactic-environment is to get the transformer environment of a macro transformer:

          (transformer
           (lambda (exp env)
             (capture-syntactic-environment
              (lambda (transformer-env)
                ...))))

Identifiers
...........

This section describes the procedures that create and manipulate identifiers.  Previous syntactic closure proposals did not have an identifier data type -- they just used symbols.  The identifier data type extends the syntactic closures facility to be compatible with the high-level syntax-rules facility.

As discussed earlier, an identifier is either a symbol or an alias.  An alias is implemented as a syntactic closure whose form is an identifier:

     (make-syntactic-closure env '() 'a)
        => an alias

Aliases are implemented as syntactic closures because they behave just like syntactic closures most of the time.  The difference is that an alias may be bound to a new value (for example by lambda or let-syntax); other syntactic closures may not be used this way. If an alias is bound, then within the scope of that binding it is looked up in the syntactic environment just like any other identifier.

Aliases are used in the implementation of the high-level facility syntax-rules.  A macro transformer created by syntax-rules uses a template to generate its output form, substituting subforms of the input form into the template.  In a syntactic closures implementation, all of the symbols in the template are replaced by aliases closed in the transformer environment, while the output form itself is closed in the usage environment.  This guarantees that the macro transformation is hygienic, without requiring the transformer to know the syntactic roles of the substituted input subforms.

 -- Function: identifier? object
     Returns #t if OBJECT is an identifier, otherwise returns #f.  Examples:

          (identifier? 'a)
             => #t
          (identifier? (make-syntactic-closure env '() 'a))
             => #t
          (identifier? "a")
             => #f
          (identifier? #\a)
             => #f
          (identifier? 97)
             => #f
          (identifier? #f)
             => #f
          (identifier? '(a))
             => #f
          (identifier? '#(a))
             => #f

     The predicate eq? is used to determine if two identifers are ``the same''.  Thus eq? can be used to compare identifiers exactly as it would be used to compare symbols.  Often, though, it is useful to know whether two identifiers ``mean the same thing''.  For example, the cond macro uses the symbol else to identify the final clause in the conditional.  A macro transformer for cond cannot just look for the symbol else, because the cond form might be the output of another macro transformer that replaced the symbol else with an alias.  Instead the transformer must look for an identifier that ``means the same thing'' in the usage environment as the symbol else means in the transformer environment.

 -- Function: identifier=? environment1 identifier1 environment2 identifier2
     ENVIRONMENT1 and ENVIRONMENT2 must be syntactic environments, and IDENTIFIER1 and IDENTIFIER2 must be identifiers.  identifier=? returns #t if the meaning of IDENTIFIER1 in ENVIRONMENT1 is the same as that of IDENTIFIER2 in ENVIRONMENT2, otherwise it returns #f. Examples:

          (let-syntax
              ((foo
                (transformer
                 (lambda (form env)
                   (capture-syntactic-environment
                    (lambda (transformer-env)
                      (identifier=? transformer-env 'x env 'x)))))))
            (list (foo)
                  (let ((x 3))
                    (foo))))
             => (#t #f)

          (let-syntax ((bar foo))
            (let-syntax
                ((foo
                  (transformer
                   (lambda (form env)
                     (capture-syntactic-environment
                      (lambda (transformer-env)
                        (identifier=? transformer-env 'foo
                                      env (cadr form))))))))
              (list (foo foo)
                    (foobar))))
             => (#f #t)

Acknowledgements
................

The syntactic closures facility was invented by Alan Bawden and Jonathan Rees.  The use of aliases to implement syntax-rules was invented by Alan Bawden (who prefers to call them synthetic names).  Much of this proposal is derived from an earlier proposal by Alan Bawden.

Syntax-Case Macros
==================

(require 'syntax-case)

 -- Function: macro:expand expression
 -- Function: syncase:expand expression
     Returns scheme code with the macros and derived expression types of EXPRESSION expanded to primitive expression types.

 -- Function: macro:eval expression
 -- Function: syncase:eval expression
     macro:eval returns the value of EXPRESSION in the current top level environment.  EXPRESSION can contain macro definitions. Side effects of EXPRESSION will affect the top level environment.

 -- Procedure: macro:load filename
 -- Procedure: syncase:load filename
     FILENAME should be a string.  If filename names an existing file, the macro:load procedure reads Scheme source code expressions and definitions from the file and evaluates them sequentially.  These source code expressions and definitions may contain macro definitions. The macro:load procedure does not affect the values returned by current-input-port and current-output-port.

This is version 2.1 of syntax-case, the low-level macro facility proposed and implemented by Robert Hieb and R. Kent Dybvig.

This version is further adapted by Harald Hanche-Olsen <hanche @ imf.unit.no> to make it compatible with, and easily usable with, SLIB.  Mainly, these adaptations consisted of:

  * Removing white space from expand.pp to save space in the distribution.  This file is not meant for human readers anyway...

  * Removed a couple of Chez scheme dependencies.

  * Renamed global variables used to minimize the possibility of name conflicts.

  * Adding an SLIB-specific initialization file.

  * Removing a couple extra files, most notably the documentation (but see below).

If you wish, you can see exactly what changes were done by reading the shell script in the file syncase.sh.

The two PostScript files were omitted in order to not burden the SLIB distribution with them.  If you do intend to use syntax-case, however, you should get these files and print them out on a PostScript printer.  They are available with the original syntax-case distribution by anonymous FTP in cs.indiana.edu:/pub/scheme/syntax-case.

In order to use syntax-case from an interactive top level, execute:

     (require 'syntax-case)
     (require 'repl)
     (repl:top-level macro:eval)

See the section Repl (see Repl) for more information.

To check operation of syntax-case get cs.indiana.edu:/pub/scheme/syntax-case, and type

     (require 'syntax-case)
     (syncase:sanity-check)

Beware that syntax-case takes a long time to load -- about 20s on a SPARCstation SLC (with SCM) and about 90s on a Macintosh SE/30 (with Gambit).

Notes
-----

All R4RS syntactic forms are defined, including delay.  Along with delay are simple definitions for make-promise (into which delay expressions expand) and force.

syntax-rules and with-syntax (described in TR356) are defined.

syntax-case is actually defined as a macro that expands into calls to the procedure syntax-dispatch and the core form syntax-lambda; do not redefine these names.

Several other top-level bindings not documented in TR356 are created:

  * the ``hooks'' in hooks.ss

  * the build- procedures in output.ss

  * expand-syntax (the expander)

The syntax of define has been extended to allow (define ID), which assigns ID to some unspecified value.

We have attempted to maintain R4RS compatibility where possible.  The incompatibilities should be confined to hooks.ss.  Please let us know if there is some incompatibility that is not flagged as such.

Send bug reports, comments, suggestions, and questions to Kent Dybvig (dyb @ iuvax.cs.indiana.edu).

Note from maintainer
--------------------

Included with the syntax-case files was structure.scm which defines a macro define-structure.  There is no documentation for this macro and it is not used by any code in SLIB.

Fluid-Let
=========

(require 'fluid-let)

 -- Syntax: fluid-let (BINDINGS ...) FORMS...

     (fluid-let ((VARIABLE INIT) ...)
        EXPRESSION EXPRESSION ...)

The INITs are evaluated in the current environment (in some unspecified order), the current values of the VARIABLEs are saved, the results are assigned to the VARIABLEs, the EXPRESSIONs are evaluated sequentially in the current environment, the VARIABLEs are restored to their original values, and the value of the last EXPRESSION is returned.

The syntax of this special form is similar to that of let, but fluid-let temporarily rebinds existing VARIABLEs.  Unlike let, fluid-let creates no new bindings; instead it assigns the values of each INIT to the binding (determined by the rules of lexical scoping) of its corresponding VARIABLE.

Yasos
=====

(require 'oop) or (require 'yasos)

`Yet Another Scheme Object System' is a simple object system for Scheme based on the paper by Norman Adams and Jonathan Rees: Object Oriented Programming in Scheme, Proceedings of the 1988 ACM Conference on LISP and Functional Programming, July 1988 [ACM #552880].

Another reference is:

Ken Dickey. Scheming with Objects AI Expert Volume 7, Number 10 (October 1992), pp. 24-33.

Terms
-----

Object
     Any Scheme data object.

Instance
     An instance of the OO system; an object.

Operation
     A METHOD.

Notes:
     The object system supports multiple inheritance.  An instance can inherit from 0 or more ancestors.  In the case of multiple inherited operations with the same identity, the operation used is that from the first ancestor which contains it (in the ancestor let).  An operation may be applied to any Scheme data object---not just instances. As code which creates instances is just code, there are no classes and no meta-ANYTHING.  Method dispatch is by a procedure call a la CLOS rather than by send syntax a la Smalltalk.

Disclaimer:
     There are a number of optimizations which can be made.  This implementation is expository (although performance should be quite reasonable).  See the L&FP paper for some suggestions.

Interface
---------

 -- Syntax: define-operation (opname self arg ...) DEFAULT-BODY
     Defines a default behavior for data objects which don't handle the operation OPNAME.  The default behavior (for an empty DEFAULT-BODY) is to generate an error.

 -- Syntax: define-predicate opname?
     Defines a predicate OPNAME?, usually used for determining the type of an object, such that (OPNAME? OBJECT) returns #t if OBJECT has an operation OPNAME? and #f otherwise.

 -- Syntax: object ((NAME SELF ARG ...) BODY) ...
     Returns an object (an instance of the object system) with operations. Invoking (NAME OBJECT ARG ... executes the BODY of the OBJECT with SELF bound to OBJECT and with argument(s) ARG....

 -- Syntax: object-with-ancestors ((ancestor1 init1) ...) operation ...
     A let-like form of object for multiple inheritance.  It returns an object inheriting the behaviour of ANCESTOR1 etc.  An operation will be invoked in an ancestor if the object itself does not provide such a method.  In the case of multiple inherited operations with the same identity, the operation used is the one found in the first ancestor in the ancestor list.

 -- Syntax: operate-as component operation self arg ...
     Used in an operation definition (of SELF) to invoke the OPERATION in an ancestor COMPONENT but maintain the object's identity.  Also known as ``send-to-super''.

 -- Procedure: print obj port
     A default print operation is provided which is just (format PORT OBJ) (see Format) for non-instances and prints OBJ preceded by #<INSTANCE> for instances.

 -- Function: size obj
     The default method returns the number of elements in OBJ if it is a vector, string or list, 2 for a pair, 1 for a character and by default id an error otherwise.  Objects such as collections (see Collections) may override the default in an obvious way.

Setters
-------

Setters implement generalized locations for objects associated with some sort of mutable state.  A getter operation retrieves a value from a generalized location and the corresponding setter operation stores a value into the location.  Only the getter is named -- the setter is specified by a procedure call as below.  (Dylan uses special syntax.)  Typically, but not necessarily, getters are access operations to extract values from Yasos objects (see Yasos). Several setters are predefined, corresponding to getters car, cdr, string-ref and vector-ref e.g., (setter car) is equivalent to set-car!.

This implementation of setters is similar to that in Dylan(TM) (Dylan: An object-oriented dynamic language, Apple Computer Eastern Research and Technology).  Common LISP provides similar facilities through setf.

 -- Function: setter getter
     Returns the setter for the procedure GETTER.  E.g., since string-ref is the getter corresponding to a setter which is actually string-set!:

          (define foo "foo")
          ((setter string-ref) foo 0 #\F) ; set element 0 of foo
          foo => "Foo"

 -- Syntax: set place new-value
     If PLACE is a variable name, set is equivalent to set!.  Otherwise, PLACE must have the form of a procedure call, where the procedure name refers to a getter and the call indicates an accessible generalized location, i.e., the call would return a value. The return value of set is usually unspecified unless used with a setter whose definition guarantees to return a useful value.

          (set (string-ref foo 2) #\O)  ; generalized location with getter
          foo => "FoO"
          (set foo "foo")               ; like set!
          foo => "foo"

 -- Procedure: add-setter getter setter
     Add procedures GETTER and SETTER to the (inaccessible) list of valid setter/getter pairs.  SETTER implements the store operation corresponding to the GETTER access operation for the relevant state.  The return value is unspecified.

 -- Procedure: remove-setter-for getter
     Removes the setter corresponding to the specified GETTER from the list of valid setters.  The return value is unspecified.

 -- Syntax: define-access-operation getter-name
     Shorthand for a Yasos define-operation defining an operation GETTER-NAME that objects may support to return the value of some mutable state.  The default operation is to signal an error.  The return value is unspecified.

Examples
--------

     ;;; These definitions for PRINT and SIZE are
     ;;; already supplied by
     (require 'yasos)

     (define-operation (print obj port)
       (format port
               (if (instance? obj) "#<instance>" "~s")
               obj))

     (define-operation (size obj)
       (cond
        ((vector? obj) (vector-length obj))
        ((list?   obj) (length obj))
        ((pair?   obj) 2)
        ((string? obj) (string-length obj))
        ((char?   obj) 1)
        (else
         (error "Operation not supported: size" obj))))

     (define-predicate cell?)
     (define-operation (fetch obj))
     (define-operation (store! obj newValue))

     (define (make-cell value)
       (object
        ((cell? self) #t)
        ((fetch self) value)
        ((store! self newValue)
         (set! value newValue)
         newValue)
        ((size self) 1)
        ((print self port)
         (format port "#<Cell: ~s>" (fetch self)))))

     (define-operation (discard obj value)
       (format #t "Discarding ~s~%" value))

     (define (make-filtered-cell value filter)
       (object-with-ancestors
        ((cell (make-cell value)))
        ((store! self newValue)
        (if (filter newValue)
            (store! cell newValue)
            (discard self newValue)))))

     (define-predicate array?)
     (define-operation (array-ref array index))
     (define-operation (array-set! array index value))

     (define (make-array num-slots)
       (let ((anArray (make-vector num-slots)))
         (object
          ((array? self) #t)
          ((size self) num-slots)
          ((array-ref self index)
           (vector-ref  anArray index))
          ((array-set! self index newValue)
           (vector-set! anArray index newValue))
          ((print self port)
           (format port "#<Array ~s>" (size self))))))

     (define-operation (position obj))
     (define-operation (discarded-value obj))

     (define (make-cell-with-history value filter size)
       (let ((pos 0) (most-recent-discard #f))
         (object-with-ancestors
          ((cell (make-filtered-call value filter))
           (sequence (make-array size)))
          ((array? self) #f)
          ((position self) pos)
          ((store! self newValue)
           (operate-as cell store! self newValue)
           (array-set! self pos newValue)
           (set! pos (+ pos 1)))
          ((discard self value)
           (set! most-recent-discard value))
          ((discarded-value self) most-recent-discard)
          ((print self port)
           (format port "#<Cell-with-history ~s>"
                   (fetch self))))))

     (define-access-operation fetch)
     (add-setter fetch store!)
     (define foo (make-cell 1))
     (print foo #f)
     => "#<Cell: 1>"
     (set (fetch foo) 2)
     =>
     (print foo #f)
     => "#<Cell: 2>"
     (fetch foo)
     => 2

Textual Conversion Packages
***************************

Precedence Parsing
==================

(require 'precedence-parse) or (require 'parse)

This package implements:

  * a Pratt style precedence parser;

  * a tokenizer which congeals tokens according to assigned classes of constituent characters;

  * procedures giving direct control of parser rulesets;

  * procedures for higher level specification of rulesets.

Precedence Parsing Overview
---------------------------

This package offers improvements over previous parsers.

  * Common computer language constructs are concisely specified.

  * Grammars can be changed dynamically.  Operators can be assigned different meanings within a lexical context.

  * Rulesets don't need compilation.  Grammars can be changed incrementally.

  * Operator precedence is specified by integers.

  * All possibilities of bad input are handled  (How do I know this? I parsed 250kbyte of random input (an e-mail file) with a non-trivial grammar utilizing all constructs.) and return as much structure as was parsed when the error occured; The symbol ? is substituted for missing input.

Here are the higher-level syntax types and an example of each. Precedence considerations are omitted for clarity.  See Grammar Rule Definition for full details.
 -- Grammar: nofix bye exit

          bye

     calls the function exit with no arguments.

 -- Grammar: prefix - negate

          - 42

     Calls the function negate with the argument 42.

 -- Grammar: infix - difference

          x - y

     Calls the function difference with arguments x and y.

 -- Grammar: nary + sum

          x + y + z

     Calls the function sum with arguments x, y, and y.

 -- Grammar: postfix ! factorial

          5 !

     Calls the function factorial with the argument 5.

 -- Grammar: prestfix set set!

          set foo bar

     Calls the function set! with the arguments foo and bar.

 -- Grammar: commentfix /* */

          /* almost any text here */

     Ignores the comment delimited by /* and */.

 -- Grammar: matchfix { list }

          {0, 1, 2}

     Calls the function list with the arguments 0, 1, and 2.

 -- Grammar: inmatchfix ( funcall )

          f(x, y)

     Calls the function funcall with the arguments f, x, and y.

 -- Grammar: delim ;

          set foo bar;

     delimits the extent of the restfix operator set.

Ruleset Definition and Use
--------------------------

 -- Variable: *syn-defs*
     A grammar is built by one or more calls to prec:define-grammar. The rules are appended to *SYN-DEFS*.  The value of *SYN-DEFS* is the grammar suitable for passing as an argument to prec:parse.

 -- Constant: *syn-ignore-whitespace*
     Is a nearly empty grammar with whitespace characters set to group 0, which means they will not be made into tokens.  Most rulesets will want to start with *syn-ignore-whitespace*

In order to start defining a grammar, either

     (set! *syn-defs* '())

or

     (set! *syn-defs* *syn-ignore-whitespace*)

 -- Function: prec:define-grammar rule1 ...
     Appends RULE1 ... to *SYN-DEFS*. prec:define-grammar is used to define both the character classes and rules for tokens.

Once your grammar is defined, save the value of *syn-defs* in a variable (for use when calling prec:parse).

     (define my-ruleset *syn-defs*)

 -- Function: prec:parse ruleset delim
 -- Function: prec:parse ruleset delim port
     The RULESET argument must be a list of rules as constructed by prec:define-grammar and extracted from *SYN-DEFS*.

     The token DELIM may be a character, symbol, or string.  A character DELIM argument will match only a character token; i.e. a character for which no token-group is assigned.  A symbols or string will match only a token string; i.e. a token resulting from a token group.

     prec:parse reads a RULESET grammar expression delimited by DELIM from the given input PORT.  prec:parse returns the next object parsable from the given input PORT, updating PORT to point to the first character past the end of the external representation of the object.

     If an end of file is encountered in the input before any characters are found that can begin an object, then an end of file object is returned. If a delimiter (such as DELIM) is found before any characters are found that can begin an object, then #f is returned.

     The PORT argument may be omitted, in which case it defaults to the value returned by current-input-port.  It is an error to parse from a closed port.

Token definition
----------------

 -- Function: tok:char-group group chars chars-proc
     The argument CHARS may be a single character, a list of characters, or a string.  Each character in CHARS is treated as though tok:char-group was called with that character alone.

     The argument CHARS-PROC must be a procedure of one argument, a list of characters.  After tokenize has finished accumulating the characters for a token, it calls CHARS-PROC with the list of characters.  The value returned is the token which tokenize returns.

     The argument GROUP may be an exact integer or a procedure of one character argument.  The following discussion concerns the treatment which the tokenizing routine, tokenize, will accord to characters on the basis of their groups.

     When GROUP is a non-zero integer, characters whose group number is equal to or exactly one less than GROUP will continue to accumulate.  Any other character causes the accumulation to stop (until a new token is to be read).

     The GROUP of zero is special.  These characters are ignored when parsed pending a token, and stop the accumulation of token characters when the accumulation has already begun.  Whitespace characters are usually put in group 0.

     If GROUP is a procedure, then, when triggerd by the occurence of an initial (no accumulation) CHARS character, this procedure will be repeatedly called with each successive character from the input stream until the GROUP procedure returns a non-false value.

The following convenient constants are provided for use with tok:char-group.

 -- Constant: tok:decimal-digits
     Is the string "0123456789".

 -- Constant: tok:upper-case
     Is the string consisting of all upper-case letters ("ABCDEFGHIJKLMNOPQRSTUVWXYZ").

 -- Constant: tok:lower-case
     Is the string consisting of all lower-case letters ("abcdefghijklmnopqrstuvwxyz").

 -- Constant: tok:whitespaces
     Is the string consisting of all characters between 0 and 255 for which char-whitespace? returns true.

Nud and Led Definition
----------------------

This section describes advanced features.  You can skip this section on first reading.

The Null Denotation (or nud) of a token is the procedure and arguments applying for that token when Left, an unclaimed parsed expression is not extant.

The Left Denotation (or led) of a token is the procedure, arguments, and lbp applying for that token when there is a Left, an unclaimed parsed expression.

In his paper,

     Pratt, V. R. Top Down Operator Precendence. SIGACT/SIGPLAN Symposium on Principles of Programming Languages, Boston, 1973, pages 41-51

the left binding power (or lbp) was an independent property of tokens.  I think this was done in order to allow tokens with NUDs but not LEDs to also be used as delimiters, which was a problem for statically defined syntaxes.  It turns out that dynamically binding NUDs and LEDs allows them independence.

For the rule-defining procedures that follow, the variable TK may be a character, string, or symbol, or a list composed of characters, strings, and symbols.  Each element of TK is treated as though the procedure were called for each element.

Character TK arguments will match only character tokens; i.e. characters for which no token-group is assigned.  Symbols and strings will both match token strings; i.e. tokens resulting from token groups.

 -- Function: prec:make-nud tk sop arg1 ...
     Returns a rule specifying that SOP be called when TK is parsed.  If SOP is a procedure, it is called with TK and ARG1 ... as its arguments; the resulting value is incorporated into the expression being built.  Otherwise, (list SOP ARG1 ...) is incorporated.

If no NUD has been defined for a token; then if that token is a string, it is converted to a symbol and returned; if not a string, the token is returned.

 -- Function: prec:make-led tk sop arg1 ...
     Returns a rule specifying that SOP be called when TK is parsed and LEFT has an unclaimed parsed expression.  If SOP is a procedure, it is called with LEFT, TK, and ARG1 ... as its arguments; the resulting value is incorporated into the expression being built.  Otherwise, LEFT is incorporated.

If no LED has been defined for a token, and LEFT is set, the parser issues a warning.

Grammar Rule Definition
-----------------------

Here are procedures for defining rules for the syntax types introduced in Precedence Parsing Overview.

For the rule-defining procedures that follow, the variable TK may be a character, string, or symbol, or a list composed of characters, strings, and symbols.  Each element of TK is treated as though the procedure were called for each element.

For procedures prec:delim, ..., prec:prestfix, if the SOP argument is #f, then the token which triggered this rule is converted to a symbol and returned.  A false SOP argument to the procedures prec:commentfix, prec:matchfix, or prec:inmatchfix has a different meaning.

Character TK arguments will match only character tokens; i.e. characters for which no token-group is assigned.  Symbols and strings will both match token strings; i.e. tokens resulting from token groups.

 -- Function: prec:delim tk
     Returns a rule specifying that TK should not be returned from parsing; i.e. TK's function is purely syntactic.  The end-of-file is always treated as a delimiter.

 -- Function: prec:nofix tk sop
     Returns a rule specifying the following actions take place when TK is parsed:

       * If SOP is a procedure, it is called with no arguments; the resulting value is incorporated into the expression being built. Otherwise, the list of SOP is incorporated.

 -- Function: prec:prefix tk sop bp rule1 ...
     Returns a rule specifying the following actions take place when TK is parsed:

       * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect.

       * prec:parse1 is called with binding-power BP.

       * If SOP is a procedure, it is called with the expression returned from prec:parse1; the resulting value is incorporated into the expression being built.  Otherwise, the list of SOP and the expression returned from prec:parse1 is incorporated.

       * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten.

 -- Function: prec:infix tk sop lbp bp rule1 ...
     Returns a rule declaring the left-binding-precedence of the token TK is LBP and specifying the following actions take place when TK is parsed:

       * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect.

       * One expression is parsed with binding-power LBP.  If instead a delimiter is encountered, a warning is issued.

       * If SOP is a procedure, it is applied to the list of LEFT and the parsed expression; the resulting value is incorporated into the expression being built.  Otherwise, the list of SOP, the LEFT expression, and the parsed expression is incorporated.

       * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten.

 -- Function: prec:nary tk sop bp
     Returns a rule declaring the left-binding-precedence of the token TK is BP and specifying the following actions take place when TK is parsed:

       * Expressions are parsed with binding-power BP as far as they are interleaved with the token TK.

       * If SOP is a procedure, it is applied to the list of LEFT and the parsed expressions; the resulting value is incorporated into the expression being built.  Otherwise, the list of SOP, the LEFT expression, and the parsed expressions is incorporated.

 -- Function: prec:postfix tk sop lbp
     Returns a rule declaring the left-binding-precedence of the token TK is LBP and specifying the following actions take place when TK is parsed:

       * If SOP is a procedure, it is called with the LEFT expression; the resulting value is incorporated into the expression being built. Otherwise, the list of SOP and the LEFT expression is incorporated.

 -- Function: prec:prestfix tk sop bp rule1 ...
     Returns a rule specifying the following actions take place when TK is parsed:

       * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect.

       * Expressions are parsed with binding-power BP until a delimiter is reached.

       * If SOP is a procedure, it is applied to the list of parsed expressions; the resulting value is incorporated into the expression being built.  Otherwise, the list of SOP and the parsed expressions is incorporated.

       * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten.

 -- Function: prec:commentfix tk stp match rule1 ...
     Returns rules specifying the following actions take place when TK is parsed:

       * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect.

       * Characters are read until and end-of-file or a sequence of characters is read which matches the string MATCH.

       * If STP is a procedure, it is called with the string of all that was read between the TK and MATCH (exclusive).

       * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten.

     Parsing of commentfix syntax differs from the others in several ways. It reads directly from input without tokenizing; It calls STP but does not return its value; nay any value.  I added the STP argument so that comment text could be echoed.

 -- Function: prec:matchfix tk sop sep match rule1 ...
     Returns a rule specifying the following actions take place when TK is parsed:

       * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect.

       * A rule declaring the token MATCH a delimiter takes effect.

       * Expressions are parsed with binding-power 0 until the token MATCH is reached.  If the token SEP does not appear between each pair of expressions parsed, a warning is issued.

       * If SOP is a procedure, it is applied to the list of parsed expressions; the resulting value is incorporated into the expression being built.  Otherwise, the list of SOP and the parsed expressions is incorporated.

       * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten.

 -- Function: prec:inmatchfix tk sop sep match lbp rule1 ...
     Returns a rule declaring the left-binding-precedence of the token TK is LBP and specifying the following actions take place when TK is parsed:

       * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect.

       * A rule declaring the token MATCH a delimiter takes effect.

       * Expressions are parsed with binding-power 0 until the token MATCH is reached.  If the token SEP does not appear between each pair of expressions parsed, a warning is issued.

       * If SOP is a procedure, it is applied to the list of LEFT and the parsed expressions; the resulting value is incorporated into the expression being built.  Otherwise, the list of SOP, the LEFT expression, and the parsed expressions is incorporated.

       * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten.

Format (version 3.0)
====================

(require 'format)

     [file fmtdoc.txi not included]

Standard Formatted I/O
======================

stdio
-----

(require 'stdio)

requires printf and scanf and additionally defines the symbols:

 -- Variable: stdin
     Defined to be (current-input-port).

 -- Variable: stdout
     Defined to be (current-output-port).

 -- Variable: stderr
     Defined to be (current-error-port).

Standard Formatted Output
-------------------------

(require 'printf)

 -- Procedure: printf format arg1 ...
 -- Procedure: fprintf port format arg1 ...
 -- Procedure: sprintf str format arg1 ...
 -- Procedure: sprintf #f format arg1 ...
 -- Procedure: sprintf k format arg1 ...

     Each function converts, formats, and outputs its ARG1 ... arguments according to the control string FORMAT argument and returns the number of characters output.

     printf sends its output to the port (current-output-port). fprintf sends its output to the port PORT.  sprintf string-set!s locations of the non-constant string argument STR to the output characters.

     Two extensions of sprintf return new strings.  If the first argument is #f, then the returned string's length is as many characters as specified by the FORMAT and data; if the first argument is a non-negative integer K, then the length of the returned string is also bounded by K.

     The string FORMAT contains plain characters which are copied to the output stream, and conversion specifications, each of which results in fetching zero or more of the arguments ARG1 ....  The results are undefined if there are an insufficient number of arguments for the format.  If FORMAT is exhausted while some of the ARG1 ... arguments remain unused, the excess ARG1 ... arguments are ignored.

     The conversion specifications in a format string have the form:

          % [ FLAGS ] [ WIDTH ] [ . PRECISION ] [ TYPE ] CONVERSION

     An output conversion specifications consist of an initial % character followed in sequence by:

       * Zero or more flag characters that modify the normal behavior of the conversion specification.

          -
               Left-justify the result in the field.  Normally the result is right-justified.

          +
               For the signed %d and %i conversions and all inexact conversions, prefix a plus sign if the value is positive.

               For the signed %d and %i conversions, if the result doesn't start with a plus or minus sign, prefix it with a space character instead.  Since the + flag ensures that the result includes a sign, this flag is ignored if both are specified.

          #
               For inexact conversions, # specifies that the result should always include a decimal point, even if no digits follow it.  For the %g and %G conversions, this also forces trailing zeros after the decimal point to be printed where they would otherwise be elided.

               For the %o conversion, force the leading digit to be 0, as if by increasing the precision.  For %x or %X, prefix a leading 0x or 0X (respectively) to the result.  This doesn't do anything useful for the %d, %i, or %u conversions.  Using this flag produces output which can be parsed by the scanf functions with the %i conversion (see Standard Formatted Input).

          0
               Pad the field with zeros instead of spaces.  The zeros are placed after any indication of sign or base.  This flag is ignored if the - flag is also specified, or if a precision is specified for an exact converson.

       * An optional decimal integer specifying the minimum field width. If the normal conversion produces fewer characters than this, the field is padded (with spaces or zeros per the 0 flag) to the specified width.  This is a minimum width; if the normal conversion produces more characters than this, the field is not truncated.

          Alternatively, if the field width is *, the next argument in the argument list (before the actual value to be printed) is used as the field width.  The width value must be an integer.  If the value is negative it is as though the - flag is set (see above) and the absolute value is used as the field width.

       * An optional precision to specify the number of digits to be written for numeric conversions and the maximum field width for string conversions.  The precision is specified by a period (.) followed optionally by a decimal integer (which defaults to zero if omitted).

          Alternatively, if the precision is .*, the next argument in the argument list (before the actual value to be printed) is used as the precision.  The value must be an integer, and is ignored if negative. If you specify * for both the field width and precision, the field width argument precedes the precision argument.  The .* precision is an enhancement.  C library versions may not accept this syntax.

          For the %f, %e, and %E conversions, the precision specifies how many digits follow the decimal-point character.  The default precision is 6.  If the precision is explicitly 0, the decimal point character is suppressed.

          For the %g and %G conversions, the precision specifies how many significant digits to print.  Significant digits are the first digit before the decimal point, and all the digits after it.  If the precision is 0 or not specified for %g or %G, it is treated like a value of 1.  If the value being printed cannot be expressed accurately in the specified number of digits, the value is rounded to the nearest number that fits.

          For exact conversions, if a precision is supplied it specifies the minimum number of digits to appear; leading zeros are produced if necessary.  If a precision is not supplied, the number is printed with as many digits as necessary.  Converting an exact 0 with an explicit precision of zero produces no characters.

       * An optional one of l, h or L, which is ignored for numeric conversions.  It is an error to specify these modifiers for non-numeric conversions.

       * A character that specifies the conversion to be applied.

Exact Conversions
.................

b, B
     Print an integer as an unsigned binary number.

     Note: %b and %B are SLIB extensions.

d, i
     Print an integer as a signed decimal number.  %d and %i are synonymous for output, but are different when used with scanf for input (see Standard Formatted Input).

o
     Print an integer as an unsigned octal number.

u
     Print an integer as an unsigned decimal number.

x, X
     Print an integer as an unsigned hexadecimal number.  %x prints using the digits 0123456789abcdef.  %X prints using the digits 0123456789ABCDEF.

Inexact Conversions
...................

f
     Print a floating-point number in fixed-point notation.

e, E
     Print a floating-point number in exponential notation.  %e prints e between mantissa and exponont.  %E prints E between mantissa and exponont.

g, G
     Print a floating-point number in either fixed or exponential notation, whichever is more appropriate for its magnitude.  Unless an # flag has been supplied, trailing zeros after a decimal point will be stripped off.  %g prints e between mantissa and exponont. %G prints E between mantissa and exponent.

k, K
     Print a number like %g, except that an SI prefix is output after the number, which is scaled accordingly.  %K outputs a space between number and prefix, %k does not.

Other Conversions
.................

c
     Print a single character.  The - flag is the only one which can be specified.  It is an error to specify a precision.

s
     Print a string.  The - flag is the only one which can be specified.  A precision specifies the maximum number of characters to output; otherwise all characters in the string are output.

a, A
     Print a scheme expression.  The - flag left-justifies the output. The # flag specifies that strings and characters should be quoted as by write (which can be read using read); otherwise, output is as display prints.  A precision specifies the maximum number of characters to output; otherwise as many characters as needed are output.

     Note: %a and %A are SLIB extensions.

%
     Print a literal % character.  No argument is consumed.  It is an error to specify flags, field width, precision, or type modifiers with %%.

Standard Formatted Input
------------------------

(require 'scanf)

 -- Function: scanf-read-list format
 -- Function: scanf-read-list format port
 -- Function: scanf-read-list format string

 -- Macro: scanf format arg1 ...
 -- Macro: fscanf port format arg1 ...
 -- Macro: sscanf str format arg1 ...

     Each function reads characters, interpreting them according to the control string FORMAT argument.

     scanf-read-list returns a list of the items specified as far as the input matches FORMAT.  scanf, fscanf, and sscanf return the number of items successfully matched and stored.  scanf, fscanf, and sscanf also set the location corresponding to ARG1 ... using the methods:

     symbol
          set!

     car expression
          set-car!

     cdr expression
          set-cdr!

     vector-ref expression
          vector-set!

     substring expression
          substring-move-left!

     The argument to a substring expression in ARG1 ... must be a non-constant string.  Characters will be stored starting at the position specified by the second argument to substring.  The number of characters stored will be limited by either the position specified by the third argument to substring or the length of the matched string, whichever is less.

     The control string, FORMAT, contains conversion specifications and other characters used to direct interpretation of input sequences.  The control string contains:

       * White-space characters (blanks, tabs, newlines, or formfeeds) that cause input to be read (and discarded) up to the next non-white-space character.

       * An ordinary character (not %) that must match the next character of the input stream.

       * Conversion specifications, consisting of the character %, an optional assignment suppressing character *, an optional numerical maximum-field width, an optional l, h or L which is ignored, and a conversion code.

     Unless the specification contains the n conversion character (described below), a conversion specification directs the conversion of the next input field.  The result of a conversion specification is returned in the position of the corresponding argument points, unless * indicates assignment suppression.  Assignment suppression provides a way to describe an input field to be skipped.  An input field is defined as a string of characters; it extends to the next inappropriate character or until the field width, if specified, is exhausted.

          Note: This specification of format strings differs from the ANSI C and POSIX specifications.  In SLIB, white space before an input field is not skipped unless white space appears before the conversion specification in the format string.  In order to write format strings which work identically with ANSI C and SLIB, prepend whitespace to all conversion specifications except [ and c.

     The conversion code indicates the interpretation of the input field; For a suppressed field, no value is returned.  The following conversion codes are legal:

     %
          A single % is expected in the input at this point; no value is returned.

     d, D
          A decimal integer is expected.

     u, U
          An unsigned decimal integer is expected.

     o, O
          An octal integer is expected.

     x, X
          A hexadecimal integer is expected.

     i
          An integer is expected.  Returns the value of the next input item, interpreted according to C conventions; a leading 0 implies octal, a leading 0x implies hexadecimal; otherwise, decimal is assumed.

     n
          Returns the total number of bytes (including white space) read by scanf.  No input is consumed by %n.

     f, F, e, E, g, G
          A floating-point number is expected.  The input format for floating-point numbers is an optionally signed string of digits, possibly containing a radix character ., followed by an optional exponent field consisting of an E or an e, followed by an optional +, -, or space, followed by an integer.

     c, C
          WIDTH characters are expected.  The normal skip-over-white-space is suppressed in this case; to read the next non-space character, use %1s.  If a field width is given, a string is returned; up to the indicated number of characters is read.

     s, S
          A character string is expected The input field is terminated by a white-space character.  scanf cannot read a null string.

     [
          Indicates string data and the normal skip-over-leading-white-space is suppressed.  The left bracket is followed by a set of characters, called the scanset, and a right bracket; the input field is the maximal sequence of input characters consisting entirely of characters in the scanset.  ^, when it appears as the first character in the scanset, serves as a complement operator and redefines the scanset as the set of all characters not contained in the remainder of the scanset string.  Construction of the scanset follows certain conventions.  A range of characters may be represented by the construct first-last, enabling [0123456789] to be expressed [0-9].  Using this convention, first must be lexically less than or equal to last; otherwise, the dash stands for itself.  The dash also stands for itself when it is the first or the last character in the scanset.  To include the right square bracket as an element of the scanset, it must appear as the first character (possibly preceded by a ^) of the scanset, in which case it will not be interpreted syntactically as the closing bracket.  At least one character must match for this conversion to succeed.

     The scanf functions terminate their conversions at end-of-file, at the end of the control string, or when an input character conflicts with the control string.  In the latter case, the offending character is left unread in the input stream.

Program and Arguments
=====================

Getopt
------

(require 'getopt)

This routine implements Posix command line argument parsing.  Notice that returning values through global variables means that getopt is not reentrant.

 -- Variable: *optind*
     Is the index of the current element of the command line.  It is initially one.  In order to parse a new command line or reparse an old one, *OPTING* must be reset.

 -- Variable: *optarg*
     Is set by getopt to the (string) option-argument of the current option.

 -- Procedure: getopt argc argv optstring
     Returns the next option letter in ARGV (starting from (vector-ref argv *optind*)) that matches a letter in OPTSTRING.  ARGV is a vector or list of strings, the 0th of which getopt usually ignores. ARGC is the argument count, usually the length of ARGV.  OPTSTRING is a string of recognized option characters; if a character is followed by a colon, the option takes an argument which may be immediately following it in the string or in the next element of ARGV.

     *OPTIND* is the index of the next element of the ARGV vector to be processed.  It is initialized to 1 by getopt.scm, and getopt updates it when it finishes with each element of ARGV.

     getopt returns the next option character from ARGV that matches a character in OPTSTRING, if there is one that matches. If the option takes an argument, getopt sets the variable *OPTARG* to the option-argument as follows:

       * If the option was the last character in the string pointed to by an element of ARGV, then *OPTARG* contains the next element of ARGV, and *OPTIND* is incremented by 2.  If the resulting value of *OPTIND* is greater than or equal to ARGC, this indicates a missing option argument, and getopt returns an error indication.

       * Otherwise, *OPTARG* is set to the string following the option character in that element of ARGV, and *OPTIND* is incremented by 1.

     If, when getopt is called, the string (vector-ref argv *optind*) either does not begin with the character #\- or is just "-", getopt returns #f without changing *OPTIND*.  If (vector-ref argv *optind*) is the string "--", getopt returns #f after incrementing *OPTIND*.

     If getopt encounters an option character that is not contained in OPTSTRING, it returns the question-mark #\? character.  If it detects a missing option argument, it returns the colon character #\: if the first character of OPTSTRING was a colon, or a question-mark character otherwise.  In either case, getopt sets the variable GETOPT:OPT to the option character that caused the error.

     The special option "--" can be used to delimit the end of the options; #f is returned, and "--" is skipped.

     RETURN VALUE

     getopt returns the next option character specified on the command line.  A colon #\: is returned if getopt detects a missing argument and the first character of OPTSTRING was a colon #\:.

     A question-mark #\? is returned if getopt encounters an option character not in OPTSTRING or detects a missing argument and the first character of OPTSTRING was not a colon #\:.

     Otherwise, getopt returns #f when all command line options have been parsed.

     Example:

          #! /usr/local/bin/scm
          ;;;This code is SCM specific.
          (define argv (program-arguments))
          (require 'getopt)

          (define opts ":a:b:cd")
          (let loop ((opt (getopt (length argv) argv opts)))
            (case opt
              ((#\a) (print "option a: " *optarg*))
              ((#\b) (print "option b: " *optarg*))
              ((#\c) (print "option c"))
              ((#\d) (print "option d"))
              ((#\?) (print "error" getopt:opt))
              ((#\:) (print "missing arg" getopt:opt))
              ((#f) (if (< *optind* (length argv))
                        (print "argv[" *optind* "]="
                               (list-ref argv *optind*)))
                    (set! *optind* (+ *optind* 1))))
            (if (< *optind* (length argv))
                (loop (getopt (length argv) argv opts))))

          (slib:exit)

Getopt--
--------

 -- Function: getopt-- argc argv optstring
     The procedure getopt-- is an extended version of getopt which parses long option names of the form --hold-the-onions and --verbosity-level=extreme. Getopt-- behaves as getopt except for non-empty options beginning with --.

     Options beginning with -- are returned as strings rather than characters.  If a value is assigned (using =) to a long option, *optarg* is set to the value.  The = and value are not returned as part of the option string.

     No information is passed to getopt-- concerning which long options should be accepted or whether such options can take arguments. If a long option did not have an argument, *optarg will be set to #f.  The caller is responsible for detecting and reporting errors.

          (define opts ":-:b:")
          (define argc 5)
          (define argv '("foo" "-b9" "--f1" "--2=" "--g3=35234.342" "--"))
          (define *optind* 1)
          (define *optarg* #f)
          (require 'qp)
          (do ((i 5 (+ -1 i)))
              ((zero? i))
            (define opt (getopt-- argc argv opts))
            (print *optind* opt *optarg*)))
          -|
          2 #\b "9"
          3 "f1" #f
          4 "2" ""
          5 "g3" "35234.342"
          5 #f "35234.342"

Command Line
------------

(require 'read-command)

 -- Function: read-command port
 -- Function: read-command
     read-command converts a command line into a list of strings suitable for parsing by getopt.  The syntax of command lines supported resembles that of popular shells.  read-command updates PORT to point to the first character past the command delimiter.

     If an end of file is encountered in the input before any characters are found that can begin an object or comment, then an end of file object is returned.

     The PORT argument may be omitted, in which case it defaults to the value returned by current-input-port.

     The fields into which the command line is split are delimited by whitespace as defined by char-whitespace?.  The end of a command is delimited by end-of-file or unescaped semicolon (;) or newline.  Any character can be literally included in a field by escaping it with a backslach (\).

     The initial character and types of fields recognized are:

     \
          The next character has is taken literally and not interpreted as a field delimiter.  If \ is the last character before a newline, that newline is just ignored.  Processing continues from the characters after the newline as though the backslash and newline were not there.

     "
          The characters up to the next unescaped " are taken literally, according to [R4RS] rules for literal strings (see Strings (Revised(4) Scheme)).

     (, %'
          One scheme expression is read starting with this character.  The read expression is evaluated, converted to a string (using display), and replaces the expression in the returned field.

     ;
          Semicolon delimits a command.  Using semicolons more than one command can appear on a line.  Escaped semicolons and semicolons inside strings do not delimit commands.

     The comment field differs from the previous fields in that it must be the first character of a command or appear after whitespace in order to be recognized.  # can be part of fields if these conditions are not met.  For instance, ab#c is just the field ab#c.

     #
          Introduces a comment.  The comment continues to the end of the line on which the semicolon appears.  Comments are treated as whitespace by read-dommand-line and backslashes before newlines in comments are also ignored.

 -- Function: read-options-file filename
     read-options-file converts an options file into a list of strings suitable for parsing by getopt.  The syntax of options files is the same as the syntax for command lines, except that newlines do not terminate reading (only ; or end of file).

     If an end of file is encountered before any characters are found that can begin an object or comment, then an end of file object is returned.

Parameter lists
---------------

(require 'parameters)

Arguments to procedures in scheme are distinguished from each other by their position in the procedure call.  This can be confusing when a procedure takes many arguments, many of which are not often used.

A parameter-list is a way of passing named information to a procedure.  Procedures are also defined to set unused parameters to default values, check parameters, and combine parameter lists.

A PARAMETER has the form (parameter-name value1 ...).  This format allows for more than one value per parameter-name.

A PARAMETER-LIST is a list of PARAMETERs, each with a different PARAMETER-NAME.

 -- Function: make-parameter-list parameter-names
     Returns an empty parameter-list with slots for PARAMETER-NAMES.

 -- Function: parameter-list-ref parameter-list parameter-name
     PARAMETER-NAME must name a valid slot of PARAMETER-LIST. parameter-list-ref returns the value of parameter PARAMETER-NAME of PARAMETER-LIST.

 -- Function: remove-parameter parameter-name parameter-list
     Removes the parameter PARAMETER-NAME from PARAMETER-LIST. remove-parameter does not alter the argument PARAMETER-LIST.

     If there are more than one PARAMETER-NAME parameters, an error is signaled.

 -- Procedure: adjoin-parameters! parameter-list parameter1 ...
     Returns PARAMETER-LIST with PARAMETER1 ... merged in.

 -- Procedure: parameter-list-expand expanders parameter-list
     EXPANDERS is a list of procedures whose order matches the order of the PARAMETER-NAMEs in the call to make-parameter-list which created PARAMETER-LIST.  For each non-false element of EXPANDERS that procedure is mapped over the corresponding parameter value and the returned parameter lists are merged into PARAMETER-LIST.

     This process is repeated until PARAMETER-LIST stops growing.  The value returned from parameter-list-expand is unspecified.

 -- Function: fill-empty-parameters defaulters parameter-list
     DEFAULTERS is a list of procedures whose order matches the order of the PARAMETER-NAMEs in the call to make-parameter-list which created PARAMETER-LIST.  fill-empty-parameters returns a new parameter-list with each empty parameter replaced with the list returned by calling the corresponding DEFAULTER with PARAMETER-LIST as its argument.

 -- Function: check-parameters checks parameter-list
     CHECKS is a list of procedures whose order matches the order of the PARAMETER-NAMEs in the call to make-parameter-list which created PARAMETER-LIST.

     check-parameters returns PARAMETER-LIST if each CHECK of the corresponding PARAMETER-LIST returns non-false.  If some CHECK returns #f a warning is signaled.

In the following procedures ARITIES is a list of symbols.  The elements of arities can be:

single
     Requires a single parameter.

optional
     A single parameter or no parameter is acceptable.

boolean
     A single boolean parameter or zero parameters is acceptable.

nary
     Any number of parameters are acceptable.

nary1
     One or more of parameters are acceptable.

 -- Function: parameter-list->arglist positions arities parameter-list
     Returns PARAMETER-LIST converted to an argument list.  Parameters of ARITY type single and boolean are converted to the single value associated with them.  The other ARITY types are converted to lists of the value(s).

     POSITIONS is a list of positive integers whose order matches the order of the PARAMETER-NAMEs in the call to make-parameter-list which created PARAMETER-LIST.  The integers specify in which argument position the corresponding parameter should appear.

Getopt Parameter lists
----------------------

(require 'getopt-parameters)

 -- Function: getopt->parameter-list argc argv optnames arities types aliases desc ...
     Returns ARGV converted to a parameter-list.  OPTNAMES are the parameter-names.  ARITIES and TYPES are lists of symbols corresponding to OPTNAMES.

     ALIASES is a list of lists of strings or integers paired with elements of OPTNAMES.  Each one-character string will be treated as a single - option by getopt.  Longer strings will be treated as long-named options (see getopt--).

     If the ALIASES association list has only strings as its cars, then all the option-arguments after an option (and before the next option) are adjoined to that option.

     If the ALIASES association list has integers, then each (string) option will take at most one option-argument.  Unoptioned arguments are collected in a list.  A -1 alias will take the last argument in this list; +1 will take the first argument in the list.  The aliases -2 then +2; -3 then +3; ... are tried so long as a positive or negative consecutive alias is found and arguments remain in the list. Finally a 0 alias, if found, absorbs any remaining arguments.

     In all cases, if unclaimed arguments remain after processing, a warning is signaled and #f is returned.

 -- Function: getopt->arglist argc argv optnames positions arities types defaulters checks aliases desc ...
     Like getopt->parameter-list, but converts ARGV to an argument-list as specified by OPTNAMES, POSITIONS, ARITIES, TYPES, DEFAULTERS, CHECKS, and ALIASES.  If the options supplied violate the ARITIES or CHECKS constraints, then a warning is signaled and #f is returned.

These getopt functions can be used with SLIB relational databases.  For an example, see make-command-server.

If errors are encountered while processing options, directions for using the options (and argument strings DESC ...) are printed to current-error-port.

     (begin
       (set! *optind* 1)
       (getopt->parameter-list
        2
        '("cmd" "-?")
        '(flag number symbols symbols string flag2 flag3 num2 num3)
        '(boolean optional nary1 nary single boolean boolean nary nary)
        '(boolean integer symbol symbol string boolean boolean integer integer)
        '(("flag" flag)
          ("f" flag)
          ("Flag" flag2)
          ("B" flag3)
          ("optional" number)
          ("o" number)
          ("nary1" symbols)
          ("N" symbols)
          ("nary" symbols)
          ("n" symbols)
          ("single" string)
          ("s" string)
          ("a" num2)
          ("Abs" num3))))
     -|
     Usage: cmd [OPTION ARGUMENT ...] ...

       -f, --flag
       -o, --optional=<number>
       -n, --nary=<symbols> ...
       -N, --nary1=<symbols> ...
       -s, --single=<string>
           --Flag
       -B
       -a        <num2> ...
           --Abs=<num3> ...

     ERROR: getopt->parameter-list "unrecognized option" "-?"

Filenames
---------

(require 'filename) or (require 'glob)

 -- Function: filename:match?? pattern
 -- Function: filename:match-ci?? pattern
     Returns a predicate which returns a non-false value if its string argument matches (the string) PATTERN, false otherwise.  Filename matching is like glob expansion described the bash manpage, except that names beginning with . are matched and / characters are not treated specially.

     These functions interpret the following characters specially in PATTERN strings:

     *
          Matches any string, including the null string.

     ?
          Matches any single character.

     [...]
          Matches any one of the enclosed characters.  A pair of characters separated by a minus sign (-) denotes a range; any character lexically between those two characters, inclusive, is matched.  If the first character following the [ is a ! or a ^ then any character not enclosed is matched.  A - or ] may be matched by including it as the first or last character in the set.

 -- Function: filename:substitute?? pattern template
 -- Function: filename:substitute-ci?? pattern template
     Returns a function transforming a single string argument according to glob patterns PATTERN and TEMPLATE.  PATTERN and TEMPLATE must have the same number of wildcard specifications, which need not be identical.  PATTERN and TEMPLATE may have a different number of literal sections. If an argument to the function matches PATTERN in the sense of filename:match?? then it returns a copy of TEMPLATE in which each wildcard specification is replaced by the part of the argument matched by the corresponding wildcard specification in PATTERN.  A * wildcard matches the longest leftmost string possible.  If the argument does not match PATTERN then false is returned.

     TEMPLATE may be a function accepting the same number of string arguments as there are wildcard specifications in PATTERN.  In the case of a match the result of applying TEMPLATE to a list of the substrings matched by wildcard specifications will be returned, otherwise TEMPLATE will not be called and #f will be returned.

          ((filename:substitute?? "scm_[0-9]*.html" "scm5c4_??.htm")
           "scm_10.html")
          => "scm5c4_10.htm"
          ((filename:substitute?? "??" "beg?mid?end") "AZ")
          => "begAmidZend"
          ((filename:substitute?? "*na*" "?NA?") "banana")
          => "banaNA"
          ((filename:substitute?? "?*?" (lambda (s1 s2 s3) (string-append s3 s1))) "ABZ")
          => "ZA"

 -- Function: replace-suffix str old new
     STR can be a string or a list of strings.  Returns a new string (or strings) similar to str but with the suffix string OLD removed and the suffix string NEW appended.  If the end of STR does not match OLD, an error is signaled.

          (replace-suffix "/usr/local/lib/slib/batch.scm" ".scm" ".c")
          => "/usr/local/lib/slib/batch.c"

Batch
-----

(require 'batch)

The batch procedures provide a way to write and execute portable scripts for a variety of operating systems.  Each batch: procedure takes as its first argument a parameter-list (see Parameter lists).  This parameter-list argument PARMS contains named associations.  Batch currently uses 2 of these:

batch-port
     The port on which to write lines of the batch file.

batch-dialect
     The syntax of batch file to generate.  Currently supported are:

       * unix

       * dos

       * vms

       * amigaos

       * system

       * *unknown*

batch.scm uses 2 enhanced relational tables (see Using Databases) to store information linking the names of operating-systems to batch-dialectes.

 -- Function: batch:initialize! database
     Defines operating-system and batch-dialect tables and adds the domain operating-system to the enhanced relational database DATABASE.

 -- Variable: *operating-system*
     Is batch's best guess as to which operating-system it is running under. *operating-system* is set to (software-type) (see Configuration) unless (software-type) is unix, in which case finer distinctions are made.

 -- Function: batch:call-with-output-script parms file proc
     PROC should be a procedure of one argument.  If FILE is an output-port, batch:call-with-output-script writes an appropriate header to FILE and then calls PROC with FILE as the only argument.  If FILE is a string, batch:call-with-output-script opens a output-file of name FILE, writes an appropriate header to FILE, and then calls PROC with the newly opened port as the only argument.  Otherwise, batch:call-with-output-script acts as if it was called with the result of (current-output-port) as its third argument.

The rest of the batch: procedures write (or execute if batch-dialect is system) commands to the batch port which has been added to PARMS or (copy-tree PARMS) by the code:

     (adjoin-parameters! PARMS (list 'batch-port PORT))

 -- Function: batch:command parms string1 string2 ...
     Calls batch:try-command (below) with arguments, but signals an error if batch:try-command returns #f.

These functions return a non-false value if the command was successfully translated into the batch dialect and #f if not.  In the case of the system dialect, the value is non-false if the operation suceeded.

 -- Function: batch:try-command parms string1 string2 ...
     Writes a command to the batch-port in PARMS which executes the program named STRING1 with arguments STRING2 ....

 -- Function: batch:try-chopped-command parms arg1 arg2 ... list
     breaks the last argument LIST into chunks small enough so that the command:

          ARG1 ARG2 ... CHUNK

     fits withing the platform's maximum command-line length.

     batch:try-chopped-command calls batch:try-command with the command and returns non-false only if the commands all fit and batch:try-command of each command line returned non-false.

 -- Function: batch:run-script parms string1 string2 ...
     Writes a command to the batch-port in PARMS which executes the batch script named STRING1 with arguments STRING2 ....

     Note: batch:run-script and batch:try-command are not the same for some operating systems (VMS).

 -- Function: batch:comment parms line1 ...
     Writes comment lines LINE1 ... to the batch-port in PARMS.

 -- Function: batch:lines->file parms file line1 ...
     Writes commands to the batch-port in PARMS which create a file named FILE with contents LINE1 ....

 -- Function: batch:delete-file parms file
     Writes a command to the batch-port in PARMS which deletes the file named FILE.

 -- Function: batch:rename-file parms old-name new-name
     Writes a command to the batch-port in PARMS which renames the file OLD-NAME to NEW-NAME.

In addition, batch provides some small utilities very useful for writing scripts:

 -- Function: truncate-up-to path char
 -- Function: truncate-up-to path string
 -- Function: truncate-up-to path charlist
     PATH can be a string or a list of strings.  Returns PATH sans any prefixes ending with a character of the second argument.  This can be used to derive a filename moved locally from elsewhere.

          (truncate-up-to "/usr/local/lib/slib/batch.scm" "/")
          => "batch.scm"

 -- Function: string-join joiner string1 ...
     Returns a new string consisting of all the strings STRING1 ... in order appended together with the string JOINER between each adjacent pair.

 -- Function: must-be-first list1 list2
     Returns a new list consisting of the elements of LIST2 ordered so that if some elements of LIST1 are equal? to elements of LIST2, then those elements will appear first and in the order of LIST1.

 -- Function: must-be-last list1 list2
     Returns a new list consisting of the elements of LIST1 ordered so that if some elements of LIST2 are equal? to elements of LIST1, then those elements will appear last and in the order of LIST2.

 -- Function: os->batch-dialect osname
     Returns its best guess for the batch-dialect to be used for the operating-system named OSNAME.  os->batch-dialect uses the tables added to DATABASE by batch:initialize!.

Here is an example of the use of most of batch's procedures:

     (require 'databases)
     (require 'parameters)
     (require 'batch)
     (require 'glob)

     (define batch (create-database #f 'alist-table))
     (batch:initialize! batch)

     (define my-parameters
       (list (list 'batch-dialect (os->batch-dialect *operating-system*))
             (list 'operating-system *operating-system*)
             (list 'batch-port (current-output-port)))) ;gets filled in later

     (batch:call-with-output-script
      my-parameters
      "my-batch"
      (lambda (batch-port)
        (adjoin-parameters! my-parameters (list 'batch-port batch-port))
        (and
         (batch:comment my-parameters
                        "================ Write file with C program.")
         (batch:rename-file my-parameters "hello.c" "hello.c~")
         (batch:lines->file my-parameters "hello.c"
                            "#include <stdio.h>"
                            "int main(int argc, char **argv)"
                            "{"
                            "  printf(\"hello world\\n\");"
                            "  return 0;"
                            "}" )
         (batch:command my-parameters "cc" "-c" "hello.c")
         (batch:command my-parameters "cc" "-o" "hello"
                       (replace-suffix "hello.c" ".c" ".o"))
         (batch:command my-parameters "hello")
         (batch:delete-file my-parameters "hello")
         (batch:delete-file my-parameters "hello.c")
         (batch:delete-file my-parameters "hello.o")
         (batch:delete-file my-parameters "my-batch")
         )))

Produces the file my-batch:

     #! /bin/sh
     # "my-batch" script created by SLIB/batch Sun Oct 31 18:24:10 1999
     # ================ Write file with C program.
     mv -f hello.c hello.c~
     rm -f hello.c
     echo '#include <stdio.h>'>>hello.c
     echo 'int main(int argc, char **argv)'>>hello.c
     echo '{'>>hello.c
     echo '  printf("hello world\n");'>>hello.c
     echo '  return 0;'>>hello.c
     echo '}'>>hello.c
     cc -c hello.c
     cc -o hello hello.o
     hello
     rm -f hello
     rm -f hello.c
     rm -f hello.o
     rm -f my-batch

When run, my-batch prints:

     bash$ my-batch
     mv: hello.c: No such file or directory
     hello world

HTML
====

     [file htmlform.txi not included]

HTML Tables
===========

     [file db2html.txi not included]

HTTP and CGI
============

     [file http-cgi.txi not included]

Parsing HTML
============

     [file html4each.txi not included]

URI
===

     [file uri.txi not included]

Printing Scheme
===============

Generic-Write
-------------

(require 'generic-write)

generic-write is a procedure that transforms a Scheme data value (or Scheme program expression) into its textual representation and prints it.  The interface to the procedure is sufficiently general to easily implement other useful formatting procedures such as pretty printing, output to a string and truncated output.

 -- Procedure: generic-write obj display? width output

     obj
          Scheme data value to transform.

     display?
          Boolean, controls whether characters and strings are quoted.

     width
          Extended boolean, selects format:

          #f
               single line format

          integer > 0
               pretty-print (value = max nb of chars per line)

     output
          Procedure of 1 argument of string type, called repeatedly with successive substrings of the textual representation.  This procedure can return #f to stop the transformation.

     The value returned by generic-write is undefined.

     Examples:

          (write obj) == (generic-write obj #f #f DISPLAY-STRING)
          (display obj) == (generic-write obj #t #f DISPLAY-STRING)

     where

          DISPLAY-STRING ==
          (lambda (s) (for-each write-char (string->list s)) #t)

Object-To-String
----------------

(require 'object->string)

     [file obj2str.txi not included]

Pretty-Print
------------

(require 'pretty-print)

 -- Procedure: pretty-print obj
 -- Procedure: pretty-print obj port

     pretty-prints OBJ on PORT.  If PORT is not specified, current-output-port is used.

     Example:

          (pretty-print '((1 2 3 4 5) (6 7 8 9 10) (11 12 13 14 15)
                          (16 17 18 19 20) (21 22 23 24 25)))
             -| ((1 2 3 4 5)
             -|  (6 7 8 9 10)
             -|  (11 12 13 14 15)
             -|  (16 17 18 19 20)
             -|  (21 22 23 24 25))

 -- Procedure: pretty-print->string obj
 -- Procedure: pretty-print->string obj width

     Returns the string of OBJ pretty-printed in WIDTH columns.  If WIDTH is not specified, (output-port-width) is used.

     Example:

          (pretty-print->string '((1 2 3 4 5) (6 7 8 9 10) (11 12 13 14 15)
                                  (16 17 18 19 20) (21 22 23 24 25)))
          =>
          "((1 2 3 4 5)
           (6 7 8 9 10)
           (11 12 13 14 15)
           (16 17 18 19 20)
           (21 22 23 24 25))
          "

          (pretty-print->string '((1 2 3 4 5) (6 7 8 9 10) (11 12 13 14 15)
                                  (16 17 18 19 20) (21 22 23 24 25))
                                16)
          =>
          "((1 2 3 4 5)
           (6 7 8 9 10)
           (11
            12
            13
            14
            15)
           (16
            17
            18
            19
            20)
           (21
            22
            23
            24
            25))
          "

(require 'pprint-file)

 -- Procedure: pprint-file infile
 -- Procedure: pprint-file infile outfile
     Pretty-prints all the code in INFILE.  If OUTFILE is specified, the output goes to OUTFILE, otherwise it goes to (current-output-port).

 -- Function: pprint-filter-file infile proc outfile
 -- Function: pprint-filter-file infile proc
     INFILE is a port or a string naming an existing file.  Scheme source code expressions and definitions are read from the port (or file) and PROC is applied to them sequentially.

     OUTFILE is a port or a string.  If no OUTFILE is specified then current-output-port is assumed.  These expanded expressions are then pretty-printed to this port.

     Whitepsace and comments (introduced by ;) which are not part of scheme expressions are reproduced in the output.  This procedure does not affect the values returned by current-input-port and current-output-port.

pprint-filter-file can be used to pre-compile macro-expansion and thus can reduce loading time.  The following will write into exp-code.scm the result of expanding all defmacros in code.scm.

     (require 'pprint-file)
     (require 'defmacroexpand)
     (defmacro:load "my-macros.scm")
     (pprint-filter-file "code.scm" defmacro:expand* "exp-code.scm")

Time and Date
=============

If (provided? 'current-time):

The procedures current-time, difftime, and offset-time deal with a calendar time datatype which may or may not be disjoint from other Scheme datatypes.

 -- Function: current-time
     Returns the time since 00:00:00 GMT, January 1, 1970, measured in seconds.  Note that the reference time is different from the reference time for get-universal-time in Common-Lisp Time.

 -- Function: difftime caltime1 caltime0
     Returns the difference (number of seconds) between twe calendar times: CALTIME1 - CALTIME0.  CALTIME0 may also be a number.

 -- Function: offset-time caltime offset
     Returns the calendar time of CALTIME offset by OFFSET number of seconds (+ caltime offset).

Time Zone
---------

(require 'time-zone)

 -- Data Format: TZ-string

     POSIX standards specify several formats for encoding time-zone rules.

     :<pathname>
          If the first character of <pathname> is /, then <pathname> specifies the absolute pathname of a tzfile(5) format time-zone file.  Otherwise, <pathname> is interpreted as a pathname within TZFILE:VICINITY (/usr/lib/zoneinfo/) naming a tzfile(5) format time-zone file.

     <std><offset>
          The string <std> consists of 3 or more alphabetic characters. <offset> specifies the time difference from GMT.  The <offset> is positive if the local time zone is west of the Prime Meridian and negative if it is east.  <offset> can be the number of hours or hours and minutes (and optionally seconds) separated by :.  For example, -4:30.

     <std><offset><dst>
          <dst> is the at least 3 alphabetic characters naming the local daylight-savings-time.

     <std><offset><dst><doffset>
          <doffset> specifies the offset from the Prime Meridian when daylight-savings-time is in effect.

     The non-tzfile formats can optionally be followed by transition times specifying the day and time when a zone changes from standard to daylight-savings and back again.

     ,<date>/<time>,<date>/<time>
          The <time>s are specified like the <offset>s above, except that leading + and - are not allowed.

          Each <date> has one of the formats:

          J<day>
               specifies the Julian day with <day> between 1 and 365.  February 29 is never counted and cannot be referenced.

          <day>
               This specifies the Julian day with n between 0 and 365.  February 29 is counted in leap years and can be specified.

          M<month>.<week>.<day>
               This specifies day <day> (0 <= <day> <= 6) of week <week> (1 <= <week> <= 5) of month <month> (1 <= <month> <= 12).  Week 1 is the first week in which day d occurs and week 5 is the last week in which day <day> occurs.  Day 0 is a Sunday.

 -- Data Type: time-zone
     is a datatype encoding how many hours from Greenwich Mean Time the local time is, and the Daylight Savings Time rules for changing it.

 -- Function: time-zone TZ-string
     Creates and returns a time-zone object specified by the string TZ-STRING.  If time-zone cannot interpret TZ-STRING, #f is returned.

 -- Function: tz:params caltime tz
     TZ is a time-zone object.  tz:params returns a list of three items:

      0. An integer.  0 if standard time is in effect for timezone TZ at CALTIME; 1 if daylight savings time is in effect for timezone TZ at CALTIME.

      1. The number of seconds west of the Prime Meridian timezone TZ is at CALTIME.

      2. The name for timezone TZ at CALTIME.

     tz:params is unaffected by the default timezone; inquiries can be made of any timezone at any calendar time.

The rest of these procedures and variables are provided for POSIX compatability.  Because of shared state they are not thread-safe.

 -- Function: tzset
     Returns the default time-zone.

 -- Function: tzset tz
     Sets (and returns) the default time-zone to TZ.

 -- Function: tzset TZ-string
     Sets (and returns) the default time-zone to that specified by TZ-STRING.

     tzset also sets the variables *TIMEZONE*, DAYLIGHT?, and TZNAME.  This function is automatically called by the time conversion procedures which depend on the time zone (see Time and Date).

 -- Variable: *timezone*
     Contains the difference, in seconds, between Greenwich Mean Time and local standard time (for example, in the U.S.  Eastern time zone (EST), timezone is 5*60*60).  *timezone* is initialized by tzset.

 -- Variable: daylight?
     is #t if the default timezone has rules for Daylight Savings Time.  Note: DAYLIGHT? does not tell you when Daylight Savings Time is in effect, just that the default zone sometimes has Daylight Savings Time.

 -- Variable: tzname
     is a vector of strings.  Index 0 has the abbreviation for the standard timezone; If DAYLIGHT?, then index 1 has the abbreviation for the Daylight Savings timezone.

Posix Time
----------

     (require 'posix-time)

 -- Data Type: Calendar-Time
     is a datatype encapsulating time.

 -- Data Type: Coordinated Universal Time
     (abbreviated UTC) is a vector of integers representing time:

      0. seconds (0 - 61)

      1. minutes (0 - 59)

      2. hours since midnight (0 - 23)

      3. day of month (1 - 31)

      4. month (0 - 11).  Note difference from decode-universal-time.

      5. the number of years since 1900.  Note difference from decode-universal-time.

      6. day of week (0 - 6)

      7. day of year (0 - 365)

      8. 1 for daylight savings, 0 for regular time

 -- Function: gmtime caltime
     Converts the calendar time CALTIME to UTC and returns it.

 -- Function: localtime caltime tz
     Returns CALTIME converted to UTC relative to timezone TZ.

 -- Function: localtime caltime
     converts the calendar time CALTIME to a vector of integers expressed relative to the user's time zone.  localtime sets the variable *TIMEZONE* with the difference between Coordinated Universal Time (UTC) and local standard time in seconds (see tzset).

 -- Function: gmktime univtime
     Converts a vector of integers in GMT Coordinated Universal Time (UTC) format to a calendar time.

 -- Function: mktime univtime
     Converts a vector of integers in local Coordinated Universal Time (UTC) format to a calendar time.

 -- Function: mktime univtime tz
     Converts a vector of integers in Coordinated Universal Time (UTC) format (relative to time-zone TZ) to calendar time.

 -- Function: asctime univtime
     Converts the vector of integers CALTIME in Coordinated Universal Time (UTC) format into a string of the form "Wed Jun 30 21:49:08 1993".

 -- Function: gtime caltime
 -- Function: ctime caltime
 -- Function: ctime caltime tz
     Equivalent to (asctime (gmtime CALTIME)), (asctime (localtime CALTIME)), and (asctime (localtime CALTIME TZ)), respectively.

Common-Lisp Time
----------------

 -- Function: get-decoded-time
     Equivalent to (decode-universal-time (get-universal-time)).

 -- Function: get-universal-time
     Returns the current time as Universal Time, number of seconds since 00:00:00 Jan 1, 1900 GMT.  Note that the reference time is different from current-time.

 -- Function: decode-universal-time univtime
     Converts UNIVTIME to Decoded Time format. Nine values are returned:

      0. seconds (0 - 61)

      1. minutes (0 - 59)

      2. hours since midnight

      3. day of month

      4. month (1 - 12).  Note difference from gmtime and localtime.

      5. year (A.D.).  Note difference from gmtime and localtime.

      6. day of week (0 - 6)

      7. #t for daylight savings, #f otherwise

      8. hours west of GMT (-24 - +24)

     Notice that the values returned by decode-universal-time do not match the arguments to encode-universal-time.

 -- Function: encode-universal-time second minute hour date month year
 -- Function: encode-universal-time second minute hour date month year time-zone
     Converts the arguments in Decoded Time format to Universal Time format. If TIME-ZONE is not specified, the returned time is adjusted for daylight saving time.  Otherwise, no adjustment is performed.

     Notice that the values returned by decode-universal-time do not match the arguments to encode-universal-time.

Schmooz
=======

     [file schmooz.texi not included]

Mathematical Packages
*********************

Bit-Twiddling
=============

(require 'logical)

The bit-twiddling functions are made available through the use of the logical package.  logical is loaded by inserting (require 'logical) before the code that uses these functions.  These functions behave as though operating on integers in two's-complement representation.

Bitwise Operations
------------------

 -- Function: logand n1 n1
     Returns the integer which is the bit-wise AND of the two integer arguments.

     Example:

          (number->string (logand #b1100 #b1010) 2)
             => "1000"

 -- Function: logior n1 n2
     Returns the integer which is the bit-wise OR of the two integer arguments.

     Example:

          (number->string (logior #b1100 #b1010) 2)
             => "1110"

 -- Function: logxor n1 n2
     Returns the integer which is the bit-wise XOR of the two integer arguments.

     Example:

          (number->string (logxor #b1100 #b1010) 2)
             => "110"

 -- Function: lognot n
     Returns the integer which is the 2s-complement of the integer argument.

     Example:

          (number->string (lognot #b10000000) 2)
             => "-10000001"
          (number->string (lognot #b0) 2)
             => "-1"

 -- Function: bitwise-if mask n0 n1
     Returns an integer composed of some bits from integer N0 and some from integer N1.  A bit of the result is taken from N0 if the corresponding bit of integer MASK is 1 and from N1 if that bit of MASK is 0.

 -- Function: logtest j k

          (logtest j k) == (not (zero? (logand j k)))

          (logtest #b0100 #b1011) => #f
          (logtest #b0100 #b0111) => #t

 -- Function: logcount n
     Returns the number of bits in integer N.  If integer is positive, the 1-bits in its binary representation are counted.  If negative, the 0-bits in its two's-complement binary representation are counted.  If 0, 0 is returned.

     Example:

          (logcount #b10101010)
             => 4
          (logcount 0)
             => 0
          (logcount -2)
             => 1

Bit Within Word
---------------

 -- Function: logbit? index j

          (logbit? index j) == (logtest (integer-expt 2 index) j)

          (logbit? 0 #b1101) => #t
          (logbit? 1 #b1101) => #f
          (logbit? 2 #b1101) => #t
          (logbit? 3 #b1101) => #t
          (logbit? 4 #b1101) => #f

 -- Function: copy-bit index from bit
     Returns an integer the same as FROM except in the INDEXth bit, which is 1 if BIT is #t and 0 if BIT is #f.

     Example:

          (number->string (copy-bit 0 0 #t) 2)       => "1"
          (number->string (copy-bit 2 0 #t) 2)       => "100"
          (number->string (copy-bit 2 #b1111 #f) 2)  => "1011"

Fields of Bits
--------------

 -- Function: bit-field n start end
     Returns the integer composed of the START (inclusive) through END (exclusive) bits of N.  The STARTth bit becomes the 0-th bit in the result.

     This function was called bit-extract in previous versions of SLIB.

     Example:

          (number->string (bit-field #b1101101010 0 4) 2)
             => "1010"
          (number->string (bit-field #b1101101010 4 9) 2)
             => "10110"

 -- Function: copy-bit-field to start end from
     Returns an integer the same as TO except possibly in the START (inclusive) through END (exclusive) bits, which are the same as those of FROM.  The 0-th bit of FROM becomes the STARTth bit of the result.

     Example:

          (number->string (copy-bit-field #b1101101010 0 4 0) 2)
                  => "1101100000"
          (number->string (copy-bit-field #b1101101010 0 4 -1) 2)
                  => "1101101111"

 -- Function: ash n count
     Returns an integer equivalent to (inexact->exact (floor (* N (expt 2 COUNT)))).

     Example:

          (number->string (ash #b1 3) 2)
             => "1000"
          (number->string (ash #b1010 -1) 2)
             => "101"

 -- Function: integer-length n
     Returns the number of bits neccessary to represent N.

     Example:

          (integer-length #b10101010)
             => 8
          (integer-length 0)
             => 0
          (integer-length #b1111)
             => 4

 -- Function: integer-expt n k
     Returns N raised to the non-negative integer exponent K.

     Example:

          (integer-expt 2 5)
             => 32
          (integer-expt -3 3)
             => -27

Bit order and Lamination
------------------------

 -- Function: logical:rotate k count len
     Returns the low-order LEN bits of K cyclically permuted COUNT bits towards high-order.

     Example:

          (number->string (logical:rotate #b0100 3 4) 2)
          => "10"
          (number->string (logical:rotate #b0100 -1 4) 2)
          => "10"

 -- Function: bit-reverse k n
     Returns the low-order K bits of N with the bit order reversed.  The low-order bit of N is the high order bit of the returned value.

          (number->string (bit-reverse 8 #xa7) 16)
            => "e5"

 -- Function: integer->list k len
 -- Function: integer->list k
     integer->list returns a list of LEN booleans corresponding to each bit of the given integer.  #t is coded for each 1; #f for 0. The LEN argument defaults to (integer-length K).

 -- Function: list->integer list
     list->integer returns an integer formed from the booleans in the list LIST, which must be a list of booleans.  A 1 bit is coded for each #t; a 0 bit for #f.

     integer->list and list->integer are inverses so far as equal? is concerned.

 -- Function: booleans->integer bool1 ...
     Returns the integer coded by the BOOL1 ... arguments.

 -- Function: bitwise:laminate k1 ...
     Returns an integer composed of the bits of K1 ... interlaced in argument order.  Given K1, ... KN, the n low-order bits of the returned value will be the lowest-order bit of each argument.

 -- Function: bitwise:delaminate count k
     Returns a list of COUNT integers comprised of every COUNTh bit of the integer K.

     For any non-negative integers K and COUNT:

          (eqv? k (bitwise:laminate (bitwise:delaminate count k)))

Gray code
---------

A Gray code is an ordering of non-negative integers in which exactly one bit differs between each pair of successive elements.  There are multiple Gray codings.  An n-bit Gray code corresponds to a Hamiltonian cycle on an n-dimensional hypercube.

Gray codes find use communicating incrementally changing values between asynchronous agents.  De-laminated Gray codes comprise the coordinates of Hilbert's space-filling curves.

 -- Function: integer->gray-code k
     Converts K to a Gray code of the same integer-length as K.

 -- Function: gray-code->integer k
     Converts the Gray code K to an integer of the same integer-length as K.

     For any non-negative integer K,

          (eqv? k (gray-code->integer (integer->gray-code k)))

 -- Function: = k1 k2
 -- Function: gray-code<? k1 k2
 -- Function: gray-code>? k1 k2
 -- Function: gray-code<=? k1 k2
 -- Function: gray-code>=? k1 k2
     These procedures return #t if their Gray code arguments are (respectively): equal, monotonically increasing, monotonically decreasing, monotonically nondecreasing, or monotonically nonincreasing.

     For any non-negative integers K1 and K2, the Gray code predicate of (integer->gray-code k1) and (integer->gray-code k2) will return the same value as the corresponding predicate of K1 and K2.

Modular Arithmetic
==================

(require 'modular)

 -- Function: mod x1 x2
 -- Function: rem x1 x2

     These procedures implement the Common-Lisp functions of the same names. The real number X2 must be non-zero. mod returns (- X1 (* X2 (floor (/ X1 X2)))). rem returns (- X1 (* X2 (truncate (/ X1 X2)))).

     If X1 and X2 are integers, then mod behaves like modulo and rem behaves like remainder.

          (mod -90 360)                          => 270
          (rem -90 180)                          => -90

          (mod 540 360)                          => 180
          (rem 540 360)                          => 180

          (mod (* 5/2 pi) (* 2 pi))              => 1.5707963267948965
          (rem (* -5/2 pi) (* 2 pi))             => -1.5707963267948965

 -- Function: extended-euclid n1 n2
     Returns a list of 3 integers (d x y) such that d = gcd(N1, N2) = N1 * x + N2 * y.

 -- Function: symmetric:modulus n
     Returns (quotient (+ -1 n) -2) for positive odd integer N.

 -- Function: modulus->integer modulus
     Returns the non-negative integer characteristic of the ring formed when MODULUS is used with modular: procedures.

 -- Function: modular:normalize modulus n
     Returns the integer (modulo N (modulus->integer MODULUS)) in the representation specified by MODULUS.

The rest of these functions assume normalized arguments; That is, the arguments are constrained by the following table:

For all of these functions, if the first argument (MODULUS) is:

positive?
     Work as before.  The result is between 0 and MODULUS.

zero?
     The arguments are treated as integers.  An integer is returned.

negative?
     The arguments and result are treated as members of the integers modulo (+ 1 (* -2 MODULUS)), but with symmetric representation; i.e. (<= (- MODULUS) N MODULUS).

If all the arguments are fixnums the computation will use only fixnums.

 -- Function: modular:invertable? modulus k
     Returns #t if there exists an integer n such that K * n == 1 mod MODULUS, and #f otherwise.

 -- Function: modular:invert modulus n2
     Returns an integer n such that 1 = (n * N2) mod MODULUS.  If N2 has no inverse mod MODULUS an error is signaled.

 -- Function: modular:negate modulus n2
     Returns (-N2) mod MODULUS.

 -- Function: modular:+ modulus n2 n3
     Returns (N2 + N3) mod MODULUS.

 -- Function: modular:- modulus n2 n3
     Returns (N2 - N3) mod MODULUS.

 -- Function: modular:* modulus n2 n3
     Returns (N2 * N3) mod MODULUS.

     The Scheme code for modular:* with negative MODULUS is not completed for fixnum-only implementations.

 -- Function: modular:expt modulus n2 n3
     Returns (N2 ^ N3) mod MODULUS.

Prime Numbers
=============

(require 'factor)

     [file factor.txi not included]

Random Numbers
==============

(require 'random)

A pseudo-random number generator is only as good as the tests it passes. George Marsaglia of Florida State University developed a battery of tests named DIEHARD (http://stat.fsu.edu/~geo/diehard.html). diehard.c has a bug which the patch http://swissnet.ai.mit.edu/ftpdir/users/jaffer/diehard.c.pat corrects.

SLIB's new PRNG generates 8 bits at a time.  With the degenerate seed 0, the numbers generated pass DIEHARD; but when bits are combined from sequential bytes, tests fail.  With the seed http://swissnet.ai.mit.edu/~jaffer/SLIB.html, all of those tests pass.

     [file random.txi not included]

If inexact numbers are supported by the Scheme implementation, randinex.scm will be loaded as well.  randinex.scm contains procedures for generating inexact distributions.

     [file randinex.txi not included]

Fast Fourier Transform
======================

(require 'fft)

 -- Function: fft array
     ARRAY is an array of (expt 2 n) numbers.  fft returns an array of complex numbers comprising the Discrete Fourier Transform of ARRAY.

 -- Function: fft-1 array
     fft-1 returns an array of complex numbers comprising the inverse Discrete Fourier Transform of ARRAY.

(fft-1 (fft ARRAY)) will return an array of values close to ARRAY.

     (fft '#(1 0+i -1 0-i 1 0+i -1 0-i)) =>

     #(0.0 0.0 0.0+628.0783185208527e-18i 0.0
       0.0 0.0 8.0-628.0783185208527e-18i 0.0)

     (fft-1 '#(0 0 0 0 0 0 8 0)) =>

     #(1.0 -61.23031769111886e-18+1.0i -1.0 61.23031769111886e-18-1.0i
       1.0 -61.23031769111886e-18+1.0i -1.0 61.23031769111886e-18-1.0i)

Cyclic Checksum
===============

(require 'crc)

Cyclic Redundancy Checks using Galois field GF(2) polynomial arithmetic are used for error detection in many data transmission and storage applications.

The generator polynomials for various CRC protocols are availble from many sources.  But the polynomial is just one of many parameters which must match in order for a CRC implementation to interoperate with existing systems:

  * the byte-order and bit-order of the data stream;

  * whether the CRC or its inverse is being calculated;

  * the initial CRC value; and

  * whether and where the CRC value is appended (inverted or non-inverted) to the data stream.

There is even some controversy over the polynomials themselves.

 -- Constant: crc-32-polynomial
     For CRC-32, http://www2.sis.pitt.edu/~jkabara/tele-2100/lect08.html gives x^32+x^26+x^23+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x^1+1.

     But http://www.cs.ncl.ac.uk/people/harry.whitfield/home.formal/CRCs.html, http://duchon.umuc.edu/Web_Pages/duchon/99_f_cm435/ShiftRegister.htm, http://spinroot.com/spin/Doc/Book91_PDF/ch3.pdf, http://www.erg.abdn.ac.uk/users/gorry/course/dl-pages/crc.html, http://www.rad.com/networks/1994/err_con/crc_most.htm, and http://www.gpfn.sk.ca/~rhg/csc8550s02/crc.html, http://www.nobugconsulting.ro/crc.php give x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.

     Although these differ in bit 22, they calculate the identical sums.

 -- Constant: crc-ccitt-polynomial

     http://www.math.grin.edu/~rebelsky/Courses/CS364/2000S/Outlines/outline.12.html, http://duchon.umuc.edu/Web_Pages/duchon/99_f_cm435/ShiftRegister.htm, http://www.cs.ncl.ac.uk/people/harry.whitfield/home.formal/CRCs.html, http://www2.sis.pitt.edu/~jkabara/tele-2100/lect08.html, and http://www.gpfn.sk.ca/~rhg/csc8550s02/crc.html give CRC-CCITT: x^16+x^12+x^5+1.

 -- Constant: crc-16-polynomial

     http://www.math.grin.edu/~rebelsky/Courses/CS364/2000S/Outlines/outline.12.html, http://duchon.umuc.edu/Web_Pages/duchon/99_f_cm435/ShiftRegister.htm, http://www.cs.ncl.ac.uk/people/harry.whitfield/home.formal/CRCs.html, http://www.gpfn.sk.ca/~rhg/csc8550s02/crc.html, and http://www.usb.org/developers/data/crcdes.pdf give CRC-16: x^16+x^15+x^2+1.

 -- Constant: crc-12-polynomial

     http://www.math.grin.edu/~rebelsky/Courses/CS364/2000S/Outlines/outline.12.html, http://www.cs.ncl.ac.uk/people/harry.whitfield/home.formal/CRCs.html, http://www.it.iitb.ac.in/it605/lectures/link/node4.html, and http://spinroot.com/spin/Doc/Book91_PDF/ch3.pdf give CRC-12: x^12+x^11+x^3+x^2+1.

     But http://www.ffldusoe.edu/Faculty/Denenberg/Topics/Networks/Error_Detection_Correction/crc.html, http://duchon.umuc.edu/Web_Pages/duchon/99_f_cm435/ShiftRegister.htm, http://www.eng.uwi.tt/depts/elec/staff/kimal/errorcc.html, http://www.ee.uwa.edu.au/~roberto/teach/itc314/java/CRC/, http://www.gpfn.sk.ca/~rhg/csc8550s02/crc.html, and http://www.efg2.com/Lab/Mathematics/CRC.htm give CRC-12: x^12+x^11+x^3+x^2+x+1.

     These differ in bit 1 and calculations using them return different values.  With citations evenly split, it is hard to know which is correct.

 -- Constant: crc-10-polynomial

     http://www.math.grin.edu/~rebelsky/Courses/CS364/2000S/Outlines/outline.12.html gives CRC-10: x^10+x^9+x^5+x^4+1; but http://cell-relay.indiana.edu/cell-relay/publications/software/CRC/crc10.html, http://www.it.iitb.ac.in/it605/lectures/link/node4.html, http://www.gpfn.sk.ca/~rhg/csc8550s02/crc.html, http://www.techfest.com/networking/atm/atm.htm, http://www.protocols.com/pbook/atmcell2.htm, and http://www.nobugconsulting.ro/crc.php give CRC-10: x^10+x^9+x^5+x^4+x+1.

 -- Constant: crc-08-polynomial

     http://www.math.grin.edu/~rebelsky/Courses/CS364/2000S/Outlines/outline.12.html, http://www.cs.ncl.ac.uk/people/harry.whitfield/home.formal/CRCs.html, http://www.it.iitb.ac.in/it605/lectures/link/node4.html, and http://www.nobugconsulting.ro/crc.php give CRC-8: x^8+x^2+x^1+1

 -- Constant: atm-hec-polynomial

     http://cell-relay.indiana.edu/cell-relay/publications/software/CRC/32bitCRC.tutorial.html and http://www.gpfn.sk.ca/~rhg/csc8550s02/crc.html give ATM HEC: x^8+x^2+x+1.

 -- Constant: dowcrc-polynomial

     http://www.cs.ncl.ac.uk/people/harry.whitfield/home.formal/CRCs.html gives DOWCRC: x^8+x^5+x^4+1.

 -- Constant: usb-token-polynomial

     http://www.usb.org/developers/data/crcdes.pdf and http://www.nobugconsulting.ro/crc.php give USB-token: x^5+x^2+1.

Each of these polynomial constants is a string of 1s and 0s, the exponent of each power of X in descending order.

 -- Function: crc:make-table poly

     POLY must be string of 1s and 0s beginning with 1 and having length greater than 8.  crc:make-table returns a vector of 256 integers, such that:

          (set! CRC
                (logxor (ash (logand (+ -1 (ash 1 (- DEG 8))) CRC) 8)
                        (vector-ref CRC-TABLE
                                    (logxor (ash CRC (- 8 DEG)) BYTE))))

     will compute the CRC with the 8 additional bits in BYTE; where CRC is the previous accumulated CRC value, DEG is the degree of POLY, and CRC-TABLE is the vector returned by crc:make-table.

     If the implementation does not support DEG-bit integers, then crc:make-table returns #f.

 -- Function: cksum file

     Computes the P1003.2/D11.2 (POSIX.2) 32-bit checksum of FILE.

          (require 'crc)
          (cksum (in-vicinity (library-vicinity) "ratize.scm"))
          => 157103930

 -- Function: cksum port
     Computes the checksum of the bytes read from PORT until the end-of-file.

 -- Function: cksum-string str

     Returns the P1003.2/D11.2 (POSIX.2) 32-bit checksum of the bytes in STR.

 -- Function: crc16 file

     Computes the USB data-packet (16-bit) CRC of FILE.

 -- Function: crc16 port
     Computes the USB data-packet (16-bit) CRC of the bytes read from PORT until the end-of-file.

     crc16 calculates the same values as the crc16.pl program given in http://www.usb.org/developers/data/crcdes.pdf.

 -- Function: crc5 file

     Computes the USB token (5-bit) CRC of FILE.

 -- Function: crc5 port
     Computes the USB token (5-bit) CRC of the bytes read from PORT until the end-of-file.

     crc5 calculates the same values as the crc5.pl program given in http://www.usb.org/developers/data/crcdes.pdf.

Plotting
========

(require 'charplot)

 -- Variable: charplot:dimensions
     A list of the maximum height (number of lines) and maximum width (number of columns) for the graph, its scales, and labels.

     The default value for CHARPLOT:DIMENSIONS is the output-port-height and output-port-width of current-output-port.

 -- Procedure: plot coords x-label y-label
     COORDS is a list or vector of coordinates, lists of x and y coordinates.  X-LABEL and Y-LABEL are strings with which to label the x and y axes.

     Example:

          (require 'charplot)
          (set! charplot:dimensions '(19 45))

          (define (make-points n)
            (if (zero? n)
                '()
                (cons (cons (/ n 6) (sin (/ n 6))) (make-points (1- n)))))

          (plot (make-points 37) "x" "Sin(x)")
          -|

            Sin(x)   ____________________________________________
                1.25|-                                           |
                    |                                            |
                   1|-       ****                                |
                    |      **    **                              |
                0.75|-    *        *                             |
                    |    *          *                            |
                 0.5|-  *            *                           |
                    |  *                                         |
                0.25|-                *                          |
                    | *                *                         |
                   0|-------------------*------------------------|
                    |                                     *      |
               -0.25|-                   *               *       |
                    |                     *             *        |
                -0.5|-                     *                     |
                    |                       *          *         |
               -0.75|-                       *        *          |
                    |                         **    **           |
                  -1|-                          ****             |
                    |:_____._____:_____._____:_____._____:_____._|
               x                 2           4           6

 -- Procedure: plot func x1 x2
 -- Procedure: plot func x1 x2 npts
     Plots the function of one argument FUNC over the range X1 to X2.  If the optional integer argument NPTS is supplied, it specifies the number of points to evaluate FUNC at.

          (plot sin 0 (* 2 pi))
          -|

                     ____________________________________________
                1.25|-:                                          |
                    | :                                          |
                   1|-:       ****                               |
                    | :     **    **                             |
                0.75|-:    *        *                            |
                    | :   *          *                           |
                 0.5|-:  **          **                          |
                    | : *             *                          |
                0.25|-:**              **                        |
                    | :*                *                        |
                   0|-*------------------*-----------------------|
                    | :                  *                 *     |
               -0.25|-:                   **              **     |
                    | :                    *             *       |
                -0.5|-:                     *           **       |
                    | :                      *          *        |
               -0.75|-:                       *       **         |
                    | :                        **    **          |
                  -1|-:                          ****            |
                    |_:_____._____:_____._____:_____._____:_____.|
                      0           2           4           6

 -- Procedure: histograph data label
     Creates and displays a histogram of the numerical values contained in vector or list DATA

          (require 'random)
          (histograph (do ((idx 99 (+ -1 idx))
                           (lst '() (cons (* .02 (random:normal)) lst)))
                          ((negative? idx) lst))
                      "normal")
          -|

                     ____________________________________________
                   9|-                  :                        |
                    |                   :                        |
                   8|-               I  :                        |
                    |                I  :                        |
                   7|-             III II I                      |
                    |              III II I                      |
                   6|-             III II I   I                  |
                    |              III II I   I                  |
                   5|-             III II I  III                 |
                    |              III II I  III                 |
                   4|-            IIII IIIII III                 |
                    |             IIII IIIII III                 |
                   3|-            IIII IIIIIIIII                 |
                    |             IIII IIIIIIIII                 |
                   2|-         IIIIIII IIIIIIIII     I I I       |
                    |          IIIIIII IIIIIIIII     I I I       |
                   1|-II I III IIIIIII IIIIIIIIIII IIIIIII       |
                    | II I III IIIIIII IIIIIIIIIII IIIIIII       |
                   0|-IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII-------|
                    |____.____:____.____:____.____:____.____:____|
            normal          -0.025      0       0.025      0.05

Solid Modeling
==============

     [file solid.txi not included]

Color
=====

http://swissnet.ai.mit.edu/~jaffer/Color

The goals of this package are to provide methods to specify, compute, and transform colors in a core set of additive color spaces.  The color spaces supported should be sufficient for working with the color data encountered in practice and the literature.

Color Data-Type
---------------

(require 'color)

 -- Function: color? obj
     Returns #t if OBJ is a color.

 -- Function: color? obj typ
     Returns #t if OBJ is a color of color-space TYP.  The symbol TYP must be one of:

       * CIEXYZ

       * RGB709

       * L*a*b*

       * L*u*v*

       * sRGB

       * e-sRGB

       * L*C*h

 -- Function: make-color space arg ...
     Returns a color of type SPACE.

 -- Function: color-space color
     Returns the symbol for the color-space in which COLOR is embedded.

 -- Function: color-precision color
     For colors in digital color-spaces, color-precision returns the number of bits used for each of the R, G, and B channels of the encoding.  Otherwise, color-precision returns #f

 -- Function: color-white-point color
     Returns the white-point of COLOR in all color-spaces except CIEXYZ.

 -- Function: convert-color color space white-point
 -- Function: convert-color color space
 -- Function: convert-color color e-sRGB precision
     Converts COLOR into SPACE at optional WHITE-POINT.

External Representation
.......................

Each color encoding has an external, case-insensitive representation. To ensure portability, the white-point for all color strings is D65. (Readers may recognize these color string formats from Xlib. X11's color management system was doomed by its fiction that CRT monitors' (and X11 default) color-spaces were linear RGBi.  Unable to shed this legacy, the only practical way to view pictures on X is to ignore its color management system and use an sRGB monitor.  In this implementation the device-independent RGB709 and sRGB spaces replace the device-dependent RGBi and RGB spaces of Xlib.)

Color Space
External Representation
CIEXYZ
CIEXYZ:<X>/<Y>/<Z>
RGB709
RGBi:<R>/<G>/<B>
L*a*b*
CIELAB:<L>/<a>/<b>
L*u*v*
CIELuv:<L>/<u>/<v>
L*C*h
CIELCh:<L>/<C>/<h>

The X, Y, Z, L, A, B, U, V, C, H, R, G, and B fields are (Scheme) real numbers within the appropriate ranges.

Color Space
External Representation
sRGB
sRGB:<R>/<G>/<B>
e-sRGB10
e-sRGB10:<R>/<G>/<B>
e-sRGB12
e-sRGB12:<R>/<G>/<B>
e-sRGB16
e-sRGB16:<R>/<G>/<B>

The R, G, and B, fields are non-negative exact decimal integers within the appropriate ranges.

Several additional syntaxes are supported by string->color:

Color Space
External Representation
sRGB
sRGB:<RRGGBB>
sRGB
#<RRGGBB>
sRGB
0x<RRGGBB>
sRGB
#x<RRGGBB>

Where RRGGBB is a non-negative six-digit hexadecimal number.

 -- Function: color->string color
     Returns a string representation of COLOR.

 -- Function: string->color string
     Returns the color represented by STRING.  If STRING is not a syntactically valid notation for a color, then string->color returns #f.

White
.....

We experience color relative to the illumination around us. CIEXYZ coordinates, although subject to uniform scaling, are objective.  Thus other color spaces are specified relative to a white point in CIEXYZ coordinates.

The white point for digital color spaces is set to D65.  For the other spaces a WHITE-POINT argument can be specified.  The default if none is specified is the white-point with which the color was created or last converted; and D65 if none has been specified.

 -- Constant: D65
     Is the color of 6500.K (blackbody) illumination.  D65 is close to the average color of daylight.

 -- Constant: D50
     Is the color of 5000.K (blackbody) illumination.  D50 is the color of indoor lighting by incandescent bulbs, whose filaments have temperatures around 5000.K.

Color Spaces
------------

     [file color.txi not included]

Spectra
-------

The following functions compute colors from spectra, scale color luminance, and extract chromaticity.  XYZ is used in the names of procedures for unnormalized colors; the coordinates of CIEXYZ colors are constrained as described in Color Spaces.

(require 'color-space)

A spectrum may be represented as:

  * A procedure of one argument accepting real numbers from 380e-9 to 780e-9, the wavelength in meters; or

  * A vector of real numbers representing intensity samples evenly spaced over some range of wavelengths overlapping the range 380e-9 to 780e-9.

CIEXYZ values are calculated as dot-product with the X, Y (Luminance), and Z Spectral Tristimulus Values.  The files cie1931.xyz and cie1964.xyz in the distribution contain these CIE-defined values.

 -- Feature: cie1964
     Loads the Spectral Tristimulus Values defining CIE 1964 Supplementary Standard Colorimetric Observer.
 -- Feature: cie1931
     Loads the Spectral Tristimulus Values defining CIE 1931 Supplementary Standard Colorimetric Observer.
 -- Feature: ciexyz
     Requires Spectral Tristimulus Values, defaulting to cie1931.

(require 'cie1964) or (require 'cie1931) will load specific values used by the following spectrum conversion procedures. The spectrum conversion procedures (require 'ciexyz) to assure that a set is loaded.

 -- Function: spectrum->XYZ proc
     PROC must be a function of one argument.  spectrum->XYZ computes the CIEXYZ(1931) values for the spectrum returned by PROC when called with arguments from 380e-9 to 780e-9, the wavelength in meters.

 -- Function: spectrum->XYZ spectrum x1 x2
     X1 and X2 must be positive real numbers specifying the wavelengths (in meters) corresponding to the zeroth and last elements of vector or list SPECTRUM.  spectrum->XYZ returns the CIEXYZ(1931) values for a light source with spectral values proportional to the elements of SPECTRUM at evenly spaced wavelengths between X1 and X2.

     Compute the colors of 6500.K and 5000.K blackbody radiation:

          (require 'color-space)
          (define xyz (spectrum->XYZ (blackbody-spectrum 6500)))
          (define y_n (cadr xyz))
          (map (lambda (x) (/ x y_n)) xyz)
              => (0.9687111145512467 1.0 1.1210875945303613)

          (define xyz (spectrum->XYZ (blackbody-spectrum 5000)))
          (map (lambda (x) (/ x y_n)) xyz)
              => (0.2933441826889158 0.2988931825387761 0.25783646831201573)

 -- Function: spectrum->CIEXYZ proc
 -- Function: spectrum->CIEXYZ spectrum x1 x2
     spectrum->CIEXYZ computes the CIEXYZ(1931) values for the spectrum, scaled so their sum is 1.

 -- Function: spectrum->chromaticity proc
 -- Function: spectrum->chromaticity spectrum x1 x2
     Computes the chromaticity for the given spectrum.

 -- Function: wavelength->XYZ w
 -- Function: wavelength->chromaticity w
 -- Function: wavelength->CIEXYZ w
     W must be a number between 380e-9 to 780e-9. wavelength->XYZ returns (unnormalized) XYZ values for a monochromatic light source with wavelength W. wavelength->chromaticity returns the chromaticity for a monochromatic light source with wavelength W. wavelength->CIEXYZ returns XYZ values for the saturated color having chromaticity of a monochromatic light source with wavelength W.

 -- Function: blackbody-spectrum temp
 -- Function: blackbody-spectrum temp span
     Returns a procedure of one argument (wavelength in meters), which returns the radiance of a black body at TEMP.

     The optional argument SPAN is the wavelength analog of bandwidth. With the default SPAN of 1.nm (1e-9.m), the values returned by the procedure correspond to the power of the photons with wavelengths W to W+1e-9.

 -- Function: temperature->XYZ x
     The positive number X is a temperature in degrees kelvin. temperature->XYZ computes the CIEXYZ(1931) values for the spectrum of a black body at temperature X.

     Compute the chromaticities of 6500.K and 5000.K blackbody radiation:

          (require 'color-space)
          (XYZ->chromaticity (temperature->XYZ 6500))
              => (0.3135191660557008 0.3236456786200268)

          (XYZ->chromaticity (temperature->XYZ 5000))
              => (0.34508082841161052 0.3516084965163377)

 -- Function: temperature->CIEXYZ x
     The positive number X is a temperature in degrees kelvin. temperature->CIEXYZ computes the CIEXYZ(1931) values for the spectrum of a black body at temperature X, scaled to be just inside the RGB709 gamut.

 -- Function: XYZ:normalize xyz
     XYZ is a list of three non-negative real numbers. XYZ:normalize returns a list of numbers proportional to XYZ; scaled so their sum is 1.

 -- Function: XYZ:normalize-colors colors ...
     COLORS is a list of XYZ triples.  XYZ:normalize-colors scales all the triples by a common factor such that the maximum sum of numbers in a scaled triple is 1.

 -- Function: XYZ->chromaticity xyz
     Returns a two element list: the x and y components of XYZ normalized to 1 (= X + Y + Z).

 -- Function: chromaticity->CIEXYZ x y
     Returns the list of X, and Y, 1 - Y - X.

 -- Function: chromaticity->whitepoint x y
     Returns the CIEXYZ(1931) values having luminosity 1 and chromaticity X and Y.

Many color datasets are expressed in xyY format; chromaticity with CIE luminance (Y).  But xyY is not a CIE standard like CIEXYZ, CIELAB, and CIELUV.  Although chrominance is well defined, the luminance component is sometimes scaled to 1, sometimes to 100, but usually has no obvious range.  With no given whitepoint, the only reasonable course is to ascertain the luminance range of a dataset and normalize the values to lie from 0 to 1.

 -- Function: XYZ->xyY xyz
     Returns a three element list: the X and Y components of XYZ normalized to 1, and CIE luminance Y.

 -- Function: xyY->XYZ xyY

 -- Function: xyY:normalize-colors colors
     COLORS is a list of xyY triples.  xyY:normalize-colors scales each chromaticity so it sums to 1 or less; and divides the Y values by the maximum Y in the dataset, so all lie between 0 and 1.

 -- Function: xyY:normalize-colors colors n
     If N is positive real, then xyY:normalize-colors divides the Y values by N times the maximum Y in the dataset.

     If N is an exact non-positive integer, then xyY:normalize-colors divides the Y values by the maximum of the Ys in the dataset excepting the -N largest Y values.

     In all cases, returned Y values are limited to lie from 0 to 1.

Why would one want to normalize to other than 1?  If the sun or its reflection is the brightest object in a scene, then normalizing to its luminance will tend to make the rest of the scene very dark.  As with photographs, limiting the specular highlights looks better than darkening everything else.

The results of measurements being what they are, xyY:normalize-colors is extremely tolerant.  Negative numbers are replaced with zero, and chromaticities with sums greater than one are scaled to sum to one.

Color Difference Metrics
------------------------

 -- Function: CIE:DE* color1 color2 white-point
 -- Function: CIE:DE* color1 color2
     Returns the Euclidean distance in L*a*b* space between COLOR1 and COLOR2.

 -- Function: CIE:DE*94 color1 color2 parametric-factors
 -- Function: CIE:DE*94 color1 color2
     CIE:DE*94 measures distance in the L*C*h cylindrical color-space. The three axes are individually scaled (depending on C*) in their contributions to the total distance.

     The CIE has defined reference conditions under which the metric with default parameters can be expected to perform well.  These are:

       * The specimens are homogeneous in colour.

       * The colour difference (CIELAB) is <= 5 units.

       * They are placed in direct edge contact.

       * Each specimen subtends an angle of >4 degrees to the assessor, whose colour vision is normal.

       * They are illuminated at 1000 lux, and viewed against a background of uniform grey, with L* of 50, under illumination simulating D65.

     The PARAMETRIC-FACTORS argument is a list of 3 quantities kL, kC and kH.  PARAMETRIC-FACTORS independently adjust each colour-difference term to account for any deviations from the reference viewing conditions.  Under the reference conditions explained above, the default is kL = kC = kH = 1.

The Color Measurement Committee of The Society of Dyers and Colorists in Great Britain created a more sophisticated color-distance function for use in judging the consistency of dye lots.  With CMC:DE* it is possible to use a single value pass/fail tolerance for all shades.

 -- Function: CMC:DE* color1 color2 l c
 -- Function: CMC:DE* color1 color2
     CMC:DE* is also a L*C*h metric.  The PARAMETRIC-FACTORS argument is a list of 2 numbers L and C.  L and C parameterize this metric.  1 and 1 are recommended for perceptibility; the default, 2 and 1, for acceptability.

Color Conversions
-----------------

This package contains the low-level color conversion and color metric routines operating on lists of 3 numbers.  There is no type or range checking.

(require 'color-space)

 -- Constant: CIEXYZ:D65
     Is the color of 6500.K (blackbody) illumination.  D65 is close to the average color of daylight.

 -- Constant: CIEXYZ:D50
     Is the color of 5000.K (blackbody) illumination.  D50 is the color of indoor lighting by incandescent bulbs.

 -- Constant: CIEXYZ:A
 -- Constant: CIEXYZ:B
 -- Constant: CIEXYZ:C
 -- Constant: CIEXYZ:E
     CIE 1931 illuminants normalized to 1 = y.

 -- Function: CIEXYZ->RGB709 xyz
 -- Function: RGB709->CIEXYZ srgb

 -- Function: CIEXYZ->L*u*v* xyz white-point
 -- Function: CIEXYZ->L*u*v* xyz
 -- Function: L*u*v*->CIEXYZ L*u*v* white-point
 -- Function: L*u*v*->CIEXYZ L*u*v*
     The WHITE-POINT defaults to CIEXYZ:D65.

 -- Function: CIEXYZ->L*a*b* xyz white-point
 -- Function: CIEXYZ->L*a*b* xyz
 -- Function: L*a*b*->CIEXYZ L*a*b* white-point
 -- Function: L*a*b*->CIEXYZ L*a*b*
     The XYZ WHITE-POINT defaults to CIEXYZ:D65.

 -- Function: L*a*b*->L*C*h L*a*b*
 -- Function: L*C*h->L*a*b* L*C*h

 -- Function: CIEXYZ->sRGB xyz
 -- Function: sRGB->CIEXYZ srgb

 -- Function: CIEXYZ->e-sRGB n xyz
 -- Function: e-sRGB->CIEXYZ n srgb

 -- Function: sRGB->e-sRGB n srgb
 -- Function: e-sRGB->sRGB n srgb
     The integer N must be 10, 12, or 16.  Because sRGB and e-sRGB use the same RGB709 chromaticities, conversion between them is simpler than conversion through CIEXYZ.

Do not convert e-sRGB precision through e-sRGB->sRGB then sRGB->e-sRGB -- values would be truncated to 8-bits!

 -- Function: e-sRGB->e-sRGB n1 srgb n2
     The integers N1 and N2 must be 10, 12, or 16. e-sRGB->e-sRGB converts SRGB to e-sRGB of precision N2.

 -- Function: L*a*b*:DE lab1 lab2
     Returns the Euclidean distance between LAB1 and LAB2.

 -- Function: L*C*h:DE*94 lch1 lch2 parametric-factors
 -- Function: L*C*h:DE*94 lch1 lch2
     L*C*h:DE*94 measures distance in the L*C*h cylindrical color-space between LCH1 and LCH2.  The three axes are individually scaled (depending on C*) in their contributions to the total distance.

 -- Function: CMC-DE lch1 lch2 parametric-factors
 -- Function: CMC-DE lch1 lch2 l c
 -- Function: CMC-DE lch1 lch2 l
 -- Function: CMC-DE lch1 lch2
     CMC:DE is a L*C*h metric.  The PARAMETRIC-FACTORS argument is a list of 2 numbers L and C.  L and C parameterize this metric.  1 and 1 are recommended for perceptibility; the default, 2 and 1, for acceptability.

Color Names
-----------

     [file colornam.txi not included]

The Short List
..............

(require 'saturate)

 -- Function: saturate name
     Looks for NAME among the 19 saturated colors from Approximate Colors on CIE Chromaticity Diagram:

     reddish orange    orange          yellowish orange   yellow
     greenish yellow   yellow green    yellowish green    green
     bluish green      blue green      greenish blue      blue
     purplish blue     bluish purple   purple             reddish purple
     red purple        purplish red    red

     (http://swissnet.ai.mit.edu/~jaffer/Color/saturate.pdf).  If NAME is found, the corresponding color is returned.  Otherwise #f is returned.  Use saturate only for light source colors.

Resene Paints Limited, New Zealand's largest privately-owned and operated paint manufacturing company, has generously made their Resene RGB Values List available.

(require 'resene)

 -- Function: resene name
     Looks for NAME among the 1300 entries in the Resene color-name dictionary (http://swissnet.ai.mit.edu/~jaffer/Color/resene.pdf). If NAME is found, the corresponding color is returned.  Otherwise #f is returned.  The Resene RGB Values List is an excellent source for surface colors.

If you include the Resene RGB Values List in binary form in a program, then you must include its license with your program:

     Resene RGB Values List

     For further information refer to http://www.resene.co.nz

     Copyright Resene Paints Ltd 2001

     Permission to copy this dictionary, to modify it, to redistribute it, to distribute modified versions, and to use it for any purpose is granted, subject to the following restrictions and understandings.

      1. Any text copy made of this dictionary must include this copyright notice in full.

      2. Any redistribution in binary form must reproduce this copyright notice in the documentation or other materials provided with the distribution.

      3. Resene Paints Ltd makes no warrantee or representation that this dictionary is error-free, and is under no obligation to provide any services, by way of maintenance, update, or otherwise.

      4. There shall be no use of the name of Resene or Resene Paints Ltd in any advertising, promotional, or sales literature without prior written consent in each case.

      5. These RGB colour formulations may not be used to the detriment of Resene Paints Ltd.

Daylight
--------

     [file daylight.txi not included]

Root Finding
============

(require 'root)

 -- Function: newton:find-integer-root f df/dx x0
     Given integer valued procedure F, its derivative (with respect to its argument) DF/DX, and initial integer value X0 for which DF/DX(X0) is non-zero, returns an integer X for which F(X) is closer to zero than either of the integers adjacent to X; or returns #f if such an integer can't be found.

     To find the closest integer to a given integers square root:

          (define (integer-sqrt y)
            (newton:find-integer-root
             (lambda (x) (- (* x x) y))
             (lambda (x) (* 2 x))
             (ash 1 (quotient (integer-length y) 2))))

          (integer-sqrt 15) => 4

 -- Function: integer-sqrt y
     Given a non-negative integer Y, returns the rounded square-root of Y.

 -- Function: newton:find-root f df/dx x0 prec
     Given real valued procedures F, DF/DX of one (real) argument, initial real value X0 for which DF/DX(X0) is non-zero, and positive real number PREC, returns a real X for which abs(F(X)) is less than PREC; or returns #f if such a real can't be found.

     If PREC is instead a negative integer, newton:find-root returns the result of -PREC iterations.

H. J. Orchard, The Laguerre Method for Finding the Zeros of Polynomials, IEEE Transactions on Circuits and Systems, Vol. 36, No. 11, November 1989, pp 1377-1381.

     There are 2 errors in Orchard's Table II.  Line k=2 for starting value of 1000+j0 should have Z_k of 1.0475 + j4.1036 and line k=2 for starting value of 0+j1000 should have Z_k of 1.0988 + j4.0833.

 -- Function: laguerre:find-root f df/dz ddf/dz^2 z0 prec
     Given complex valued procedure F of one (complex) argument, its derivative (with respect to its argument) DF/DX, its second derivative DDF/DZ^2, initial complex value Z0, and positive real number PREC, returns a complex number Z for which magnitude(F(Z)) is less than PREC; or returns #f if such a number can't be found.

     If PREC is instead a negative integer, laguerre:find-root returns the result of -PREC iterations.

 -- Function: laguerre:find-polynomial-root deg f df/dz ddf/dz^2 z0 prec
     Given polynomial procedure F of integer degree DEG of one argument, its derivative (with respect to its argument) DF/DX, its second derivative DDF/DZ^2, initial complex value Z0, and positive real number PREC, returns a complex number Z for which magnitude(F(Z)) is less than PREC; or returns #f if such a number can't be found.

     If PREC is instead a negative integer, laguerre:find-polynomial-root returns the result of -PREC iterations.

 -- Function: secant:find-root f x0 x1 prec
 -- Function: secant:find-bracketed-root f x0 x1 prec
     Given a real valued procedure F and two real valued starting points X0 and X1, returns a real X for which (abs (f x)) is less than PREC; or returns #f if such a real can't be found.

     If X0 and X1 are chosen such that they bracket a root, that is

          (or (< (f x0) 0 (f x1))
              (< (f x1) 0 (f x0)))

     then the root returned will be between X0 and X1, and F will not be passed an argument outside of that interval.

     secant:find-bracketed-root will return #f unless X0 and X1 bracket a root.

     The secant method is used until a bracketing interval is found, at which point a modified regula falsi method is used.

     If PREC is instead a negative integer, secant:find-root returns the result of -PREC iterations.

     If PREC is a procedure it should accept 5 arguments: X0 F0 X1 F1 and COUNT, where F0 will be (f x0), F1 (f x1), and COUNT the number of iterations performed so far.  PREC should return non-false if the iteration should be stopped.

Minimizing
==========

(require 'minimize)

     [file minimize.txi not included]

Commutative Rings
=================

Scheme provides a consistent and capable set of numeric functions. Inexacts implement a field; integers a commutative ring (and Euclidean domain).  This package allows one to use basic Scheme numeric functions with symbols and non-numeric elements of commutative rings.

(require 'commutative-ring)

The commutative-ring package makes the procedures +, -, *, /, and ^ careful in the sense that any non-numeric arguments they do not reduce appear in the expression output.  In order to see what working with this package is like, self-set all the single letter identifiers (to their corresponding symbols).

     (define a 'a)
     ...
     (define z 'z)

Or just (require 'self-set).  Now try some sample expressions:

     (+ (+ a b) (- a b)) => (* a 2)
     (* (+ a b) (+ a b)) => (^ (+ a b) 2)
     (* (+ a b) (- a b)) => (* (+ a b) (- a b))
     (* (- a b) (- a b)) => (^ (- a b) 2)
     (* (- a b) (+ a b)) => (* (+ a b) (- a b))
     (/ (+ a b) (+ c d)) => (/ (+ a b) (+ c d))
     (^ (+ a b) 3) => (^ (+ a b) 3)
     (^ (+ a 2) 3) => (^ (+ 2 a) 3)

Associative rules have been applied and repeated addition and multiplication converted to multiplication and exponentiation.

We can enable distributive rules, thus expanding to sum of products form:

     (set! *ruleset* (combined-rulesets distribute* distribute/))

     (* (+ a b) (+ a b)) => (+ (* 2 a b) (^ a 2) (^ b 2))
     (* (+ a b) (- a b)) => (- (^ a 2) (^ b 2))
     (* (- a b) (- a b)) => (- (+ (^ a 2) (^ b 2)) (* 2 a b))
     (* (- a b) (+ a b)) => (- (^ a 2) (^ b 2))
     (/ (+ a b) (+ c d)) => (+ (/ a (+ c d)) (/ b (+ c d)))
     (/ (+ a b) (- c d)) => (+ (/ a (- c d)) (/ b (- c d)))
     (/ (- a b) (- c d)) => (- (/ a (- c d)) (/ b (- c d)))
     (/ (- a b) (+ c d)) => (- (/ a (+ c d)) (/ b (+ c d)))
     (^ (+ a b) 3) => (+ (* 3 a (^ b 2)) (* 3 b (^ a 2)) (^ a 3) (^ b 3))
     (^ (+ a 2) 3) => (+ 8 (* a 12) (* (^ a 2) 6) (^ a 3))

Use of this package is not restricted to simple arithmetic expressions:

     (require 'determinant)

     (determinant '((a b c) (d e f) (g h i))) =>
     (- (+ (* a e i) (* b f g) (* c d h)) (* a f h) (* b d i) (* c e g))

Currently, only +, -, *, /, and ^ support non-numeric elements.  Expressions with - are converted to equivalent expressions without -, so behavior for - is not defined separately.  / expressions are handled similarly.

This list might be extended to include quotient, modulo, remainder, lcm, and gcd; but these work only for the more restrictive Euclidean (Unique Factorization) Domain.

Rules and Rulesets
==================

The commutative-ring package allows control of ring properties through the use of rulesets.

 -- Variable: *ruleset*
     Contains the set of rules currently in effect.  Rules defined by cring:define-rule are stored within the value of *ruleset* at the time cring:define-rule is called.  If *RULESET* is #f, then no rules apply.

 -- Function: make-ruleset rule1 ...
 -- Function: make-ruleset name rule1 ...
     Returns a new ruleset containing the rules formed by applying cring:define-rule to each 4-element list argument RULE.  If the first argument to make-ruleset is a symbol, then the database table created for the new ruleset will be named NAME.  Calling make-ruleset with no rule arguments creates an empty ruleset.

 -- Function: combined-rulesets ruleset1 ...
 -- Function: combined-rulesets name ruleset1 ...
     Returns a new ruleset containing the rules contained in each ruleset argument RULESET.  If the first argument to combined-ruleset is a symbol, then the database table created for the new ruleset will be named NAME.  Calling combined-ruleset with no ruleset arguments creates an empty ruleset.

Two rulesets are defined by this package.

 -- Constant: distribute*
     Contains the ruleset to distribute multiplication over addition and subtraction.

 -- Constant: distribute/
     Contains the ruleset to distribute division over addition and subtraction.

     Take care when using both DISTRIBUTE* and DISTRIBUTE/ simultaneously.  It is possible to put / into an infinite loop.

You can specify how sum and product expressions containing non-numeric elements simplify by specifying the rules for + or * for cases where expressions involving objects reduce to numbers or to expressions involving different non-numeric elements.

 -- Function: cring:define-rule op sub-op1 sub-op2 reduction
     Defines a rule for the case when the operation represented by symbol OP is applied to lists whose cars are SUB-OP1 and SUB-OP2, respectively.  The argument REDUCTION is a procedure accepting 2 arguments which will be lists whose cars are SUB-OP1 and SUB-OP2.

 -- Function: cring:define-rule op sub-op1 'identity reduction
     Defines a rule for the case when the operation represented by symbol OP is applied to a list whose car is SUB-OP1, and some other argument.  REDUCTION will be called with the list whose car is SUB-OP1 and some other argument.

     If REDUCTION returns #f, the reduction has failed and other reductions will be tried.  If REDUCTION returns a non-false value, that value will replace the two arguments in arithmetic (+, -, and *) calculations involving non-numeric elements.

     The operations + and * are assumed commutative; hence both orders of arguments to REDUCTION will be tried if necessary.

     The following rule is the definition for distributing * over +.

          (cring:define-rule
           '* '+ 'identity
           (lambda (exp1 exp2)
             (apply + (map (lambda (trm) (* trm exp2)) (cdr exp1))))))

How to Create a Commutative Ring
================================

The first step in creating your commutative ring is to write procedures to create elements of the ring.  A non-numeric element of the ring must be represented as a list whose first element is a symbol or string. This first element identifies the type of the object.  A convenient and clear convention is to make the type-identifying element be the same symbol whose top-level value is the procedure to create it.

     (define (n . list1)
       (cond ((and (= 2 (length list1))
                   (eq? (car list1) (cadr list1)))
              0)
             ((not (term< (first list1) (last1 list1)))
              (apply n (reverse list1)))
             (else (cons 'n list1))))

     (define (s x y) (n x y))

     (define (m . list1)
       (cond ((neq? (first list1) (term_min list1))
              (apply m (cyclicrotate list1)))
             ((term< (last1 list1) (cadr list1))
              (apply m (reverse (cyclicrotate list1))))
             (else (cons 'm list1))))

Define a procedure to multiply 2 non-numeric elements of the ring. Other multiplicatons are handled automatically.  Objects for which rules have not been defined are not changed.

     (define (n*n ni nj)
       (let ((list1 (cdr ni)) (list2 (cdr nj)))
         (cond ((null? (intersection list1 list2)) #f)
               ((and (eq? (last1 list1) (first list2))
                     (neq? (first list1) (last1 list2)))
                (apply n (splice list1 list2)))
               ((and (eq? (first list1) (first list2))
                     (neq? (last1 list1) (last1 list2)))
                (apply n (splice (reverse list1) list2)))
               ((and (eq? (last1 list1) (last1 list2))
                     (neq? (first list1) (first list2)))
                (apply n (splice list1 (reverse list2))))
               ((and (eq? (last1 list1) (first list2))
                     (eq? (first list1) (last1 list2)))
                (apply m (cyclicsplice list1 list2)))
               ((and (eq? (first list1) (first list2))
                     (eq? (last1 list1) (last1 list2)))
                (apply m (cyclicsplice (reverse list1) list2)))
               (else #f))))

Test the procedures to see if they work.

     ;;; where cyclicrotate(list) is cyclic rotation of the list one step
     ;;; by putting the first element at the end
     (define (cyclicrotate list1)
       (append (rest list1) (list (first list1))))
     ;;; and where term_min(list) is the element of the list which is
     ;;; first in the term ordering.
     (define (term_min list1)
       (car (sort list1 term<)))
     (define (term< sym1 sym2)
       (string<? (symbol->string sym1) (symbol->string sym2)))
     (define first car)
     (define rest cdr)
     (define (last1 list1) (car (last-pair list1)))
     (define (neq? obj1 obj2) (not (eq? obj1 obj2)))
     ;;; where splice is the concatenation of list1 and list2 except that their
     ;;; common element is not repeated.
     (define (splice list1 list2)
       (cond ((eq? (last1 list1) (first list2))
              (append list1 (cdr list2)))
             (else (error 'splice list1 list2))))
     ;;; where cyclicsplice is the result of leaving off the last element of
     ;;; splice(list1,list2).
     (define (cyclicsplice list1 list2)
       (cond ((and (eq? (last1 list1) (first list2))
                   (eq? (first list1) (last1 list2)))
              (butlast (splice list1 list2) 1))
             (else (error 'cyclicsplice list1 list2))))

     (N*N (S a b) (S a b)) => (m a b)

Then register the rule for multiplying type N objects by type N objects.

     (cring:define-rule '* 'N 'N N*N))

Now we are ready to compute!

     (define (t)
       (define detM
         (+ (* (S g b)
               (+ (* (S f d)
                     (- (* (S a f) (S d g)) (* (S a g) (S d f))))
                  (* (S f f)
                     (- (* (S a g) (S d d)) (* (S a d) (S d g))))
                  (* (S f g)
                     (- (* (S a d) (S d f)) (* (S a f) (S d d))))))
            (* (S g d)
               (+ (* (S f b)
                     (- (* (S a g) (S d f)) (* (S a f) (S d g))))
                  (* (S f f)
                     (- (* (S a b) (S d g)) (* (S a g) (S d b))))
                  (* (S f g)
                     (- (* (S a f) (S d b)) (* (S a b) (S d f))))))
            (* (S g f)
               (+ (* (S f b)
                     (- (* (S a d) (S d g)) (* (S a g) (S d d))))
                  (* (S f d)
                     (- (* (S a g) (S d b)) (* (S a b) (S d g))))
                  (* (S f g)
                     (- (* (S a b) (S d d)) (* (S a d) (S d b))))))
            (* (S g g)
               (+ (* (S f b)
                     (- (* (S a f) (S d d)) (* (S a d) (S d f))))
                  (* (S f d)
                     (- (* (S a b) (S d f)) (* (S a f) (S d b))))
                  (* (S f f)
                     (- (* (S a d) (S d b)) (* (S a b) (S d d))))))))
       (* (S b e) (S c a) (S e c)
          detM
          ))
     (pretty-print (t))
     -|
     (- (+ (m a c e b d f g)
           (m a c e b d g f)
           (m a c e b f d g)
           (m a c e b f g d)
           (m a c e b g d f)
           (m a c e b g f d))
        (* 2 (m a b e c) (m d f g))
        (* (m a c e b d) (m f g))
        (* (m a c e b f) (m d g))
        (* (m a c e b g) (m d f)))

Matrix Algebra
==============

     [file determ.txi not included]

Database Packages
*****************

Base Table
==========

A base-table is the primitive database layer upon which SLIB relational databases are built.  At the minimum, it must support the types integer, symbol, string, and boolean.  The base-table may restrict the size of integers, symbols, and strings it supports.

A base table implementation is available as the value of the identifier naming it (eg. ALIST-TABLE) after requiring the symbol of that name.

 -- Feature: alist-table
     (require 'alist-table)

     Association-list base tables support all Scheme types and are suitable for small databases.  In order to be retrieved after being written to a file, the data stored should include only objects which are readable and writeable in the Scheme implementation.

     The alist-table base-table-type is included in the SLIB distribution.

 -- Feature: wb-table
     (require 'wb-table)

     WB is a B-tree database package supported by the SCM Scheme implementation.  It supports scheme expressions for keys and values whose text representations are less than 255 characters in length. Being disk-based, wb-table readily stores hundreds of megabytes of data.

This rest of this section documents the interface for a base table implementation from which the Relational Database package constructs a Relational system.  It will be of interest primarily to those wishing to port or write new base-table implementations.

 -- Variable: *base-table-implementations*
     To support automatic dispatch for open-database, each base-table module adds an association to *BASE-TABLE-IMPLEMENTATIONS* when loaded.  This association is the list of the base-table symbol and the value returned by (make-relational-system BASE-TABLE).

All of these functions are accessed through a single procedure by calling that procedure with the symbol name of the operation.  A procedure will be returned if that operation is supported and #f otherwise.  For example:

     (require 'alist-table)
     (define open-base (alist-table 'make-base))
     make-base       => *a procedure*
     (define foo (alist-table 'foo))
     foo             => #f

 -- Function: make-base filename key-dimension column-types
     Returns a new, open, low-level database (collection of tables) associated with FILENAME.  This returned database has an empty table associated with CATALOG-ID.  The positive integer KEY-DIMENSION is the number of keys composed to make a PRIMARY-KEY for the catalog table.  The list of symbols COLUMN-TYPES describes the types of each column for that table. If the database cannot be created as specified, #f is returned.

     Calling the close-base method on this database and possibly other operations will cause FILENAME to be written to.  If FILENAME is #f a temporary, non-disk based database will be created if such can be supported by the base table implelentation.

 -- Function: open-base filename mutable
     Returns an open low-level database associated with FILENAME.  If MUTABLE is #t, this database will have methods capable of effecting change to the database.  If MUTABLE is #f, only methods for inquiring the database will be available.  If the database cannot be opened as specified #f is returned.

     Calling the close-base (and possibly other) method on a MUTABLE database will cause FILENAME to be written to.

 -- Function: write-base lldb filename
     Causes the low-level database LLDB to be written to FILENAME.  If the write is successful, also causes LLDB to henceforth be associated with FILENAME.  Calling the close-database (and possibly other) method on LLDB may cause FILENAME to be written to.  If FILENAME is #f this database will be changed to a temporary, non-disk based database if such can be supported by the underlying base table implelentation.  If the operations completed successfully, #t is returned. Otherwise, #f is returned.

 -- Function: sync-base lldb
     Causes the file associated with the low-level database LLDB to be updated to reflect its current state.  If the associated filename is #f, no action is taken and #f is returned.  If this operation completes successfully, #t is returned.  Otherwise, #f is returned.

 -- Function: close-base lldb
     Causes the low-level database LLDB to be written to its associated file (if any).  If the write is successful, subsequent operations to LLDB will signal an error.  If the operations complete successfully, #t is returned.  Otherwise, #f is returned.

 -- Function: make-table lldb key-dimension column-types
     Returns the BASE-ID for a new base table, otherwise returns #f.  The base table can then be opened using (open-table LLDB BASE-ID).  The positive integer KEY-DIMENSION is the number of keys composed to make a PRIMARY-KEY for this table. The list of symbols COLUMN-TYPES describes the types of each column.

 -- Constant: catalog-id
     A constant BASE-ID suitable for passing as a parameter to open-table.  CATALOG-ID will be used as the base table for the system catalog.

 -- Function: open-table lldb base-id key-dimension column-types
     Returns a HANDLE for an existing base table in the low-level database LLDB if that table exists and can be opened in the mode indicated by MUTABLE, otherwise returns #f.

     As with make-table, the positive integer KEY-DIMENSION is the number of keys composed to make a PRIMARY-KEY for this table. The list of symbols COLUMN-TYPES describes the types of each column.

 -- Function: kill-table lldb base-id key-dimension column-types
     Returns #t if the base table associated with BASE-ID was removed from the low level database LLDB, and #f otherwise.

 -- Function: make-keyifier-1 type
     Returns a procedure which accepts a single argument which must be of type TYPE.  This returned procedure returns an object suitable for being a KEY argument in the functions whose descriptions follow.

     Any 2 arguments of the supported type passed to the returned function which are not equal? must result in returned values which are not equal?.

 -- Function: make-list-keyifier key-dimension types
     The list of symbols TYPES must have at least KEY-DIMENSION elements.  Returns a procedure which accepts a list of length KEY-DIMENSION and whose types must corresopond to the types named by TYPES.  This returned procedure combines the elements of its list argument into an object suitable for being a KEY argument in the functions whose descriptions follow.

     Any 2 lists of supported types (which must at least include symbols and non-negative integers) passed to the returned function which are not equal? must result in returned values which are not equal?.

 -- Function: make-key-extractor key-dimension types column-number
     Returns a procedure which accepts objects produced by application of the result of (make-list-keyifier KEY-DIMENSION TYPES). This procedure returns a KEY which is equal? to the COLUMN-NUMBERth element of the list which was passed to create COMBINED-KEY.  The list TYPES must have at least KEY-DIMENSION elements.

 -- Function: make-key->list key-dimension types
     Returns a procedure which accepts objects produced by application of the result of (make-list-keyifier KEY-DIMENSION TYPES). This procedure returns a list of KEYs which are elementwise equal? to the list which was passed to create COMBINED-KEY.

In the following functions, the KEY argument can always be assumed to be the value returned by a call to a keyify routine.

In contrast, a MATCH-KEYS argument is a list of length equal to the number of primary keys.  The MATCH-KEYS restrict the actions of the table command to those records whose primary keys all satisfy the corresponding element of the MATCH-KEYS list.  The elements and their actions are:

     #f
          The false value matches any key in the corresponding position.

     an object of type procedure
          This procedure must take a single argument, the key in the corresponding position.  Any key for which the procedure returns a non-false value is a match; Any key for which the procedure returns a #f is not.

     other values
          Any other value matches only those keys equal? to it.

The KEY-DIMENSION and COLUMN-TYPES arguments are needed to decode the combined-keys for matching with MATCH-KEYS.

 -- Function: for-each-key handle procedure key-dimension column-types match-keys
     Calls PROCEDURE once with each KEY in the table opened in HANDLE which satisfy MATCH-KEYS in an unspecified order. An unspecified value is returned.

 -- Function: map-key handle procedure key-dimension column-types match-keys
     Returns a list of the values returned by calling PROCEDURE once with each KEY in the table opened in HANDLE which satisfy MATCH-KEYS in an unspecified order.

 -- Function: ordered-for-each-key handle procedure key-dimension column-types match-keys
     Calls PROCEDURE once with each KEY in the table opened in HANDLE which satisfy MATCH-KEYS in the natural order for the types of the primary key fields of that table.  An unspecified value is returned.

 -- Function: delete* handle key-dimension column-types match-keys
     Removes all rows which satisfy MATCH-KEYS from the table opened in HANDLE.  An unspecified value is returned.

 -- Function: present? handle key
     Returns a non-#f value if there is a row associated with KEY in the table opened in HANDLE and #f otherwise.

 -- Function: delete handle key
     Removes the row associated with KEY from the table opened in HANDLE.  An unspecified value is returned.

 -- Function: make-getter key-dimension types
     Returns a procedure which takes arguments HANDLE and KEY. This procedure returns a list of the non-primary values of the relation (in the base table opened in HANDLE) whose primary key is KEY if it exists, and #f otherwise.

 -- Function: make-putter key-dimension types
     Returns a procedure which takes arguments HANDLE and KEY and VALUE-LIST.  This procedure associates the primary key KEY with the values in VALUE-LIST (in the base table opened in HANDLE) and returns an unspecified value.

 -- Function: supported-type? symbol
     Returns #t if SYMBOL names a type allowed as a column value by the implementation, and #f otherwise.  At a minimum, an implementation must support the types integer, symbol, string, boolean, and base-id.

 -- Function: supported-key-type? symbol
     Returns #t if SYMBOL names a type allowed as a key value by the implementation, and #f otherwise.  At a minimum, an implementation must support the types integer, and symbol.

integer
     Scheme exact integer.

symbol
     Scheme symbol.

boolean
     #t or #f.

base-id
     Objects suitable for passing as the BASE-ID parameter to open-table.  The value of CATALOG-ID must be an acceptable base-id.

Relational Database
===================

(require 'relational-database)

This package implements a database system inspired by the Relational Model (E. F. Codd, A Relational Model of Data for Large Shared Data Banks).  An SLIB relational database implementation can be created from any Base Table implementation.

Why relational database?  For motivations and design issues see http://swissnet.ai.mit.edu/~jaffer/DBManifesto.html.

Using Databases
---------------

     [file dbutil.txi not included]

Relational Database Objects
---------------------------

 -- Function: make-relational-system base-table-implementation

     Returns a procedure implementing a relational database using the BASE-TABLE-IMPLEMENTATION.

     All of the operations of a base table implementation are accessed through a procedure defined by requireing that implementation. Similarly, all of the operations of the relational database implementation are accessed through the procedure returned by make-relational-system.  For instance, a new relational database could be created from the procedure returned by make-relational-system by:

          (require 'alist-table)
          (define relational-alist-system
                  (make-relational-system alist-table))
          (define create-alist-database
                  (relational-alist-system 'create-database))
          (define my-database
                  (create-alist-database "mydata.db"))

What follows are the descriptions of the methods available from relational system returned by a call to make-relational-system.

 -- Function: create-database filename

     Returns an open, nearly empty relational database associated with FILENAME.  The only tables defined are the system catalog and domain table.  Calling the close-database method on this database and possibly other operations will cause FILENAME to be written to.  If FILENAME is #f a temporary, non-disk based database will be created if such can be supported by the underlying base table implelentation.  If the database cannot be created as specified #f is returned.  For the fields and layout of descriptor tables, Catalog Representation

 -- Function: open-database filename mutable?

     Returns an open relational database associated with FILENAME.  If MUTABLE? is #t, this database will have methods capable of effecting change to the database.  If MUTABLE? is #f, only methods for inquiring the database will be available.  Calling the close-database (and possibly other) method on a MUTABLE? database will cause FILENAME to be written to.  If the database cannot be opened as specified #f is returned.

Database Operations
-------------------

These are the descriptions of the methods available from an open relational database.  A method is retrieved from a database by calling the database with the symbol name of the operation.  For example:

     (define my-database
             (create-alist-database "mydata.db"))
     (define telephone-table-desc
             ((my-database 'create-table) 'telephone-table-desc))

 -- Function: close-database
     Causes the relational database to be written to its associated file (if any).  If the write is successful, subsequent operations to this database will signal an error.  If the operations completed successfully, #t is returned.  Otherwise, #f is returned.

 -- Function: write-database filename
     Causes the relational database to be written to FILENAME.  If the write is successful, also causes the database to henceforth be associated with FILENAME.  Calling the close-database (and possibly other) method on this database will cause FILENAME to be written to.  If FILENAME is #f this database will be changed to a temporary, non-disk based database if such can be supported by the underlying base table implelentation.  If the operations completed successfully, #t is returned.  Otherwise, #f is returned.

 -- Function: sync-database
     Causes any pending updates to the database file to be written out.  If the operations completed successfully, #t is returned. Otherwise, #f is returned.

 -- Function: solidify-database
     Causes any pending updates to the database file to be written out.  If the writes completed successfully, then the database is changed to be immutable and #t is returned.  Otherwise, #f is returned.

 -- Function: table-exists? table-name
     Returns #t if TABLE-NAME exists in the system catalog, otherwise returns #f.

 -- Function: open-table table-name mutable?
     Returns a methods procedure for an existing relational table in this database if it exists and can be opened in the mode indicated by MUTABLE?, otherwise returns #f.

These methods will be present only in mutable databases.

 -- Function: delete-table table-name
     Removes and returns the TABLE-NAME row from the system catalog if the table or view associated with TABLE-NAME gets removed from the database, and #f otherwise.

 -- Function: create-table table-desc-name
     Returns a methods procedure for a new (open) relational table for describing the columns of a new base table in this database, otherwise returns #f.  For the fields and layout of descriptor tables, see Catalog Representation.

 -- Function: create-table table-name table-desc-name
     Returns a methods procedure for a new (open) relational table with columns as described by TABLE-DESC-NAME, otherwise returns #f.

 -- Function: create-view ??
 -- Function: project-table ??
 -- Function: restrict-table ??
 -- Function: cart-prod-tables ??
     Not yet implemented.

Table Operations
----------------

These are the descriptions of the methods available from an open relational table.  A method is retrieved from a table by calling the table with the symbol name of the operation.  For example:

     (define telephone-table-desc
             ((my-database 'create-table) 'telephone-table-desc))
     (require 'common-list-functions)
     (define ndrp (telephone-table-desc 'row:insert))
     (ndrp '(1 #t name #f string))
     (ndrp '(2 #f telephone
               (lambda (d)
                 (and (string? d) (> (string-length d) 2)
                      (every
                       (lambda (c)
                         (memv c '(#\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9
                                       #\+ #\( #\  #\) #\-)))
                       (string->list d))))
               string))

Some operations described below require primary key arguments.  Primary keys arguments are denoted KEY1 KEY2 ....  It is an error to call an operation for a table which takes primary key arguments with the wrong number of primary keys for that table.

The term row used below refers to a Scheme list of values (one for each column) in the order specified in the descriptor (table) for this table.  Missing values appear as #f.  Primary keys must not be missing.

 -- Function: get column-name
     Returns a procedure of arguments KEY1 KEY2 ... which returns the value for the COLUMN-NAME column of the row associated with primary keys KEY1, KEY2 ... if that row exists in the table, or #f otherwise.

          ((plat 'get 'processor) 'djgpp) => i386
          ((plat 'get 'processor) 'be-os) => #f

 -- Function: get* column-name
     Returns a procedure of optional arguments MATCH-KEY1 ... which returns a list of the values for the specified column for all rows in this table.  The optional MATCH-KEY1 ... arguments restrict actions to a subset of the table.  See the match-key description below for details.

          ((plat 'get* 'processor)) =>
          (i386 8086 i386 8086 i386 i386 8086 m68000
           m68000 m68000 m68000 m68000 powerpc)

          ((plat 'get* 'processor) #f) =>
          (i386 8086 i386 8086 i386 i386 8086 m68000
           m68000 m68000 m68000 m68000 powerpc)

          (define (a-key? key)
             (char=? #\a (string-ref (symbol->string key) 0)))

          ((plat 'get* 'processor) a-key?) =>
          (m68000 m68000 m68000 m68000 m68000 powerpc)

          ((plat 'get* 'name) a-key?) =>
          (atari-st-turbo-c atari-st-gcc amiga-sas/c-5.10
           amiga-aztec amiga-dice-c aix)

 -- Function: row:retrieve
     Returns a procedure of arguments KEY1 KEY2 ... which returns the row associated with primary keys KEY1, KEY2 ... if it exists, or #f otherwise.

          ((plat 'row:retrieve) 'linux) => (linux i386 linux gcc)
          ((plat 'row:retrieve) 'multics) => #f

 -- Function: row:retrieve*
     Returns a procedure of optional arguments MATCH-KEY1 ... which returns a list of all rows in this table.  The optional MATCH-KEY1 ... arguments restrict actions to a subset of the table.  See the match-key description below for details.

     ((plat 'row:retrieve*) a-key?) =>
     ((atari-st-turbo-c m68000 atari turbo-c)
      (atari-st-gcc m68000 atari gcc)
      (amiga-sas/c-5.10 m68000 amiga sas/c)
      (amiga-aztec m68000 amiga aztec)
      (amiga-dice-c m68000 amiga dice-c)
      (aix powerpc aix -))

 -- Function: row:remove
     Returns a procedure of arguments KEY1 KEY2 ... which removes and returns the row associated with primary keys KEY1, KEY2 ... if it exists, or #f otherwise.

 -- Function: row:remove*
     Returns a procedure of optional arguments MATCH-KEY1 ... which removes and returns a list of all rows in this table.  The optional MATCH-KEY1 ... arguments restrict actions to a subset of the table.  See the match-key description below for details.

 -- Function: row:delete
     Returns a procedure of arguments KEY1 KEY2 ... which deletes the row associated with primary keys KEY1, KEY2 ... if it exists.  The value returned is unspecified.

 -- Function: row:delete*
     Returns a procedure of optional arguments MATCH-KEY1 ... which Deletes all rows from this table.  The optional MATCH-KEY1 ... arguments restrict deletions to a subset of the table.  See the match-key description below for details.  The value returned is unspecified.  The descriptor table and catalog entry for this table are not affected.

 -- Function: row:update
     Returns a procedure of one argument, ROW, which adds the row, ROW, to this table.  If a row for the primary key(s) specified by ROW already exists in this table, it will be overwritten.  The value returned is unspecified.

 -- Function: row:update*
     Returns a procedure of one argument, ROWS, which adds each row in the list of rows, ROWS, to this table.  If a row for the primary key specified by an element of ROWS already exists in this table, it will be overwritten.  The value returned is unspecified.

 -- Function: row:insert
     Adds the row ROW to this table.  If a row for the primary key(s) specified by ROW already exists in this table an error is signaled.  The value returned is unspecified.

 -- Function: row:insert*
     Returns a procedure of one argument, ROWS, which adds each row in the list of rows, ROWS, to this table.  If a row for the primary key specified by an element of ROWS already exists in this table, an error is signaled.  The value returned is unspecified.

 -- Function: for-each-row
     Returns a procedure of arguments PROC MATCH-KEY1 ... which calls PROC with each ROW in this table in the (implementation-dependent) natural ordering for rows.  The optional MATCH-KEY1 ... arguments restrict actions to a subset of the table.  See the match-key description below for details.

     Real relational programmers would use some least-upper-bound join for every row to get them in order; But we don't have joins yet.

The (optional) MATCH-KEY1 ... arguments are used to restrict actions of a whole-table operation to a subset of that table.  Those procedures (returned by methods) which accept match-key arguments will accept any number of match-key arguments between zero and the number of primary keys in the table.  Any unspecified MATCH-KEY arguments default to #f.

The MATCH-KEY1 ... restrict the actions of the table command to those records whose primary keys each satisfy the corresponding MATCH-KEY argument.  The arguments and their actions are:

     #f
          The false value matches any key in the corresponding position.

     an object of type procedure
          This procedure must take a single argument, the key in the corresponding position.  Any key for which the procedure returns a non-false value is a match; Any key for which the procedure returns a #f is not.

     other values
          Any other value matches only those keys equal? to it.

 -- Function: close-table
     Subsequent operations to this table will signal an error.

 -- Constant: column-names
 -- Constant: column-foreigns
 -- Constant: column-domains
 -- Constant: column-types
     Return a list of the column names, foreign-key table names, domain names, or type names respectively for this table.  These 4 methods are different from the others in that the list is returned, rather than a procedure to obtain the list.

 -- Constant: primary-limit
     Returns the number of primary keys fields in the relations in this table.

Catalog Representation
----------------------

Each database (in an implementation) has a system catalog which describes all the user accessible tables in that database (including itself).

The system catalog base table has the following fields.  PRI indicates a primary key for that table.

     PRI table-name
         column-limit            the highest column number
         coltab-name             descriptor table name
         bastab-id               data base table identifier
         user-integrity-rule
         view-procedure          A scheme thunk which, when called,
                                 produces a handle for the view.  coltab
                                 and bastab are specified if and only if
                                 view-procedure is not.

Descriptors for base tables (not views) are tables (pointed to by system catalog).  Descriptor (base) tables have the fields:

     PRI column-number           sequential integers from 1
         primary-key?            boolean TRUE for primary key components
         column-name
         column-integrity-rule
         domain-name

A primary key is any column marked as primary-key? in the corresponding descriptor table.  All the primary-key? columns must have lower column numbers than any non-primary-key? columns. Every table must have at least one primary key.  Primary keys must be sufficient to distinguish all rows from each other in the table.  All of the system defined tables have a single primary key.

This package currently supports tables having from 1 to 4 primary keys if there are non-primary columns, and any (natural) number if all columns are primary keys.  If you need more than 4 primary keys, I would like to hear what you are doing!

A domain is a category describing the allowable values to occur in a column.  It is described by a (base) table with the fields:

     PRI domain-name
         foreign-table
         domain-integrity-rule
         type-id
         type-param

The type-id field value is a symbol.  This symbol may be used by the underlying base table implementation in storing that field.

If the foreign-table field is non-#f then that field names a table from the catalog.  The values for that domain must match a primary key of the table referenced by the TYPE-PARAM (or #f, if allowed).  This package currently does not support composite foreign-keys.

The types for which support is planned are:

         atom
         symbol
         string                  [<length>]
         number                  [<base>]
         money                   <currency>
         date-time
         boolean

         foreign-key             <table-name>
         expression
         virtual                 <expression>

Embedded Commands
-----------------

(require 'database-commands)

This enhancement wraps a utility layer on relational-database which provides:

  * Automatic execution of initialization commands stored in database.

  * Transparent execution of database commands stored in *commands* table in database.

When an enhanced relational-database is called with a symbol which matches a NAME in the *commands* table, the associated procedure expression is evaluated and applied to the enhanced relational-database.  A procedure should then be returned which the user can invoke on (optional) arguments.

The command *initialize* is special.  If present in the *commands* table, open-database or open-database! will return the value of the *initialize* command.  Notice that arbitrary code can be run when the *initialize* procedure is automatically applied to the enhanced relational-database.

Note also that if you wish to shadow or hide from the user relational-database methods described in Database Operations, this can be done by a dispatch in the closure returned by the *initialize* expression rather than by entries in the *commands* table if it is desired that the underlying methods remain accessible to code in the *commands* table.

Database Extension
..................

 -- Function: wrap-command-interface rdb
     Returns relational database RDB wrapped with additional commands defined in its *commands* table.

 -- Function: add-command-tables rdb
     The relational database RDB must be mutable. ADD-COMMAND-TABLES adds a *command* table to RDB; then returns (wrap-command-interface RDB).

 -- Function: define-*commands* rdb spec-0 ...

     Adds commands to the *commands* table as specified in SPEC-0 ... to the open relational-database RDB.  Each SPEC has the form:

          ((<name> <rdb>) "comment" <expression1> <expression2> ...)

     or

          ((<name> <rdb>) <expression1> <expression2> ...)

     where <name> is the command name, <rdb> is a formal passed the calling relational database, "comment" describes the command, and <expression1>, <expression1>, ... are the body of the procedure.

     define-*commands* adds to the *commands* table a command <name>:

          (lambda (<name> <rdb>) <expression1> <expression2> ...)

 -- Function: open-command-database filename
 -- Function: open-command-database filename base-table-type
     Returns an open enhanced relational database associated with FILENAME.  The database will be opened with base-table type BASE-TABLE-TYPE) if supplied.  If BASE-TABLE-TYPE is not supplied, open-command-database will attempt to deduce the correct base-table-type.  If the database can not be opened or if it lacks the *commands* table, #f is returned.

 -- Function: open-command-database! filename
 -- Function: open-command-database! filename base-table-type
     Returns mutable open enhanced relational database ...

 -- Function: open-command-database database
     Returns DATABASE if it is an immutable relational database; #f otherwise.

 -- Function: open-command-database! database
     Returns DATABASE if it is a mutable relational database; #f otherwise.

Command Intrinsics
..................

Some commands are defined in all extended relational-databases.  The are called just like Database Operations.

 -- Function: add-domain domain-row
     Adds DOMAIN-ROW to the domains table if there is no row in the domains table associated with key (car DOMAIN-ROW) and returns #t.  Otherwise returns #f.

     For the fields and layout of the domain table, see Catalog Representation.  Currently, these fields are

       * domain-name

       * foreign-table

       * domain-integrity-rule

       * type-id

       * type-param

     The following example adds 3 domains to the build database. Optstring is either a string or #f.  filename is a string and build-whats is a symbol.

          (for-each (build 'add-domain)
                    '((optstring #f
                                 (lambda (x) (or (not x) (string? x)))
                                 string
                                 #f)
                      (filename #f #f string #f)
                      (build-whats #f #f symbol #f)))

 -- Function: delete-domain domain-name
     Removes and returns the DOMAIN-NAME row from the domains table.

 -- Function: domain-checker domain
     Returns a procedure to check an argument for conformance to domain DOMAIN.

Define-tables Example
.....................

The following example shows a new database with the name of foo.db being created with tables describing processor families and processor/os/compiler combinations.

The database command define-tables is defined to call define-tables with its arguments.  The database is also configured to print Welcome when the database is opened.  The database is then closed and reopened.

     (require 'databases)
     (define my-rdb (create-database "foo.db" 'alist-table))

     (define-tables my-rdb
       '(*commands*
         ((name symbol))
         ((parameters parameter-list)
          (procedure expression)
          (documentation string))
         ((define-tables
           no-parameters
           no-parameter-names
           (lambda (rdb) (lambda specs (apply define-tables rdb specs)))
           "Create or Augment tables from list of specs")
          (*initialize*
           no-parameters
           no-parameter-names
           (lambda (rdb) (display "Welcome") (newline) rdb)
           "Print Welcome"))))

     ((my-rdb 'define-tables)
      '(processor-family
        ((family    atom))
        ((also-ran  processor-family))
        ((m68000           #f)
         (m68030           m68000)
         (i386             8086)
         (8086             #f)
         (powerpc          #f)))

      '(platform
        ((name      symbol))
        ((processor processor-family)
         (os        symbol)
         (compiler  symbol))
        ((aix              powerpc aix     -)
         (amiga-dice-c     m68000  amiga   dice-c)
         (amiga-aztec      m68000  amiga   aztec)
         (amiga-sas/c-5.10 m68000  amiga   sas/c)
         (atari-st-gcc     m68000  atari   gcc)
         (atari-st-turbo-c m68000  atari   turbo-c)
         (borland-c-3.1    8086    ms-dos  borland-c)
         (djgpp            i386    ms-dos  gcc)
         (linux            i386    linux   gcc)
         (microsoft-c      8086    ms-dos  microsoft-c)
         (os/2-emx         i386    os/2    gcc)
         (turbo-c-2        8086    ms-dos  turbo-c)
         (watcom-9.0       i386    ms-dos  watcom))))

     ((my-rdb 'close-database))

     (set! my-rdb (open-database "foo.db" 'alist-table))
     -|
     Welcome

The *commands* Table
....................

The table *commands* in an enhanced relational-database has the fields (with domains):

     PRI name        symbol
         parameters  parameter-list
         procedure   expression
         documentation string

The parameters field is a foreign key (domain parameter-list) of the *catalog-data* table and should have the value of a table described by *parameter-columns*.  This parameter-list table describes the arguments suitable for passing to the associated command.  The intent of this table is to be of a form such that different user-interfaces (for instance, pull-down menus or plain-text queries) can operate from the same table.  A parameter-list table has the following fields:

     PRI index       uint
         name        symbol
         arity       parameter-arity
         domain      domain
         defaulter   expression
         expander    expression
         documentation string

The arity field can take the values:

single
     Requires a single parameter of the specified domain.

optional
     A single parameter of the specified domain or zero parameters is acceptable.

boolean
     A single boolean parameter or zero parameters (in which case #f is substituted) is acceptable.

nary
     Any number of parameters of the specified domain are acceptable.  The argument passed to the command function is always a list of the parameters.

nary1
     One or more of parameters of the specified domain are acceptable.  The argument passed to the command function is always a list of the parameters.

The domain field specifies the domain which a parameter or parameters in the indexth field must satisfy.

The defaulter field is an expression whose value is either #f or a procedure of one argument (the parameter-list) which returns a list of the default value or values as appropriate. Note that since the defaulter procedure is called every time a default parameter is needed for this column, sticky defaults can be implemented using shared state with the domain-integrity-rule.

Command Service
...............

 -- Function: make-command-server rdb table-name
     Returns a procedure of 2 arguments, a (symbol) command and a call-back procedure.  When this returned procedure is called, it looks up COMMAND in table TABLE-NAME and calls the call-back procedure with arguments:

     command
          The COMMAND

     command-value
          The result of evaluating the expression in the PROCEDURE field of TABLE-NAME and calling it with RDB.

     parameter-name
          A list of the official name of each parameter.  Corresponds to the name field of the COMMAND's parameter-table.

     positions
          A list of the positive integer index of each parameter.  Corresponds to the index field of the COMMAND's parameter-table.

     arities
          A list of the arities of each parameter.  Corresponds to the arity field of the COMMAND's parameter-table.  For a description of arity see table above.

     types
          A list of the type name of each parameter.  Correspnds to the type-id field of the contents of the domain of the COMMAND's parameter-table.

     defaulters
          A list of the defaulters for each parameter.  Corresponds to the defaulters field of the COMMAND's parameter-table.

     domain-integrity-rules
          A list of procedures (one for each parameter) which tests whether a value for a parameter is acceptable for that parameter.  The procedure should be called with each datum in the list for nary arity parameters.

     aliases
          A list of lists of (alias parameter-name).  There can be more than one alias per PARAMETER-NAME.

For information about parameters, see Parameter lists.

Command Example
...............

Here is an example of setting up a command with arguments and parsing those arguments from a getopt style argument list (see Getopt).

     (require 'database-commands)
     (require 'databases)
     (require 'getopt-parameters)
     (require 'parameters)
     (require 'getopt)
     (require 'fluid-let)
     (require 'printf)

     (define my-rdb (add-command-tables (create-database #f 'alist-table)))

     (define-tables my-rdb
       '(foo-params
         *parameter-columns*
         *parameter-columns*
         ((1 single-string single string
             (lambda (pl) '("str")) #f "single string")
          (2 nary-symbols nary symbol
             (lambda (pl) '()) #f "zero or more symbols")
          (3 nary1-symbols nary1 symbol
             (lambda (pl) '(symb)) #f "one or more symbols")
          (4 optional-number optional uint
             (lambda (pl) '()) #f "zero or one number")
          (5 flag boolean boolean
             (lambda (pl) '(#f)) #f "a boolean flag")))
       '(foo-pnames
         ((name string))
         ((parameter-index uint))
         (("s" 1)
          ("single-string" 1)
          ("n" 2)
          ("nary-symbols" 2)
          ("N" 3)
          ("nary1-symbols" 3)
          ("o" 4)
          ("optional-number" 4)
          ("f" 5)
          ("flag" 5)))
       '(my-commands
         ((name symbol))
         ((parameters parameter-list)
          (parameter-names parameter-name-translation)
          (procedure expression)
          (documentation string))
         ((foo
           foo-params
           foo-pnames
           (lambda (rdb) (lambda args (print args)))
           "test command arguments"))))

     (define (dbutil:serve-command-line rdb command-table
                                        command argc argv)
       (set! argv (if (vector? argv) (vector->list argv) argv))
       ((make-command-server rdb command-table)
        command
        (lambda (comname comval options positions
                         arities types defaulters dirs aliases)
          (apply comval (getopt->arglist
                         argc argv options positions
                         arities types defaulters dirs aliases)))))

     (define (cmd . opts)
       (fluid-let ((*optind* 1))
         (printf "%-34s => "
                 (call-with-output-string
                  (lambda (pt) (write (cons 'cmd opts) pt))))
         (set! opts (cons "cmd" opts))
         (force-output)
         (dbutil:serve-command-line
          my-rdb 'my-commands 'foo (length opts) opts)))

     (cmd)                              => ("str" () (symb) () #f)
     (cmd "-f")                         => ("str" () (symb) () #t)
     (cmd "--flag")                     => ("str" () (symb) () #t)
     (cmd "-o177")                      => ("str" () (symb) (177) #f)
     (cmd "-o" "177")                   => ("str" () (symb) (177) #f)
     (cmd "--optional" "621")           => ("str" () (symb) (621) #f)
     (cmd "--optional=621")             => ("str" () (symb) (621) #f)
     (cmd "-s" "speciality")            => ("speciality" () (symb) () #f)
     (cmd "-sspeciality")               => ("speciality" () (symb) () #f)
     (cmd "--single" "serendipity")     => ("serendipity" () (symb) () #f)
     (cmd "--single=serendipity")       => ("serendipity" () (symb) () #f)
     (cmd "-n" "gravity" "piety")       => ("str" () (piety gravity) () #f)
     (cmd "-ngravity" "piety")          => ("str" () (piety gravity) () #f)
     (cmd "--nary" "chastity")          => ("str" () (chastity) () #f)
     (cmd "--nary=chastity" "")         => ("str" () ( chastity) () #f)
     (cmd "-N" "calamity")              => ("str" () (calamity) () #f)
     (cmd "-Ncalamity")                 => ("str" () (calamity) () #f)
     (cmd "--nary1" "surety")           => ("str" () (surety) () #f)
     (cmd "--nary1=surety")             => ("str" () (surety) () #f)
     (cmd "-N" "levity" "fealty")       => ("str" () (fealty levity) () #f)
     (cmd "-Nlevity" "fealty")          => ("str" () (fealty levity) () #f)
     (cmd "--nary1" "surety" "brevity") => ("str" () (brevity surety) () #f)
     (cmd "--nary1=surety" "brevity")   => ("str" () (brevity surety) () #f)
     (cmd "-?")
     -|
     Usage: cmd [OPTION ARGUMENT ...] ...

       -f, --flag
       -o, --optional[=]<number>
       -n, --nary[=]<symbols> ...
       -N, --nary1[=]<symbols> ...
       -s, --single[=]<string>

     ERROR: getopt->parameter-list "unrecognized option" "-?"

Database Macros
---------------

(require 'within-database)

The object-oriented programming interface to SLIB relational databases has failed to support clear, understandable, and modular code-writing for database applications.

This seems to be a failure of the object-oriented paradigm where the type of an object is not manifest (or even traceable) in source code.

within-database, along with the databases package, reorganizes high-level database functions toward a more declarative style.  Using this package, one can tag database table and command declarations for emacs:

     etags -lscheme -r'/ *(define-\(command\|table\) (\([^; \t]+\)/\2/' \
           source1.scm ...

 -- Function: within-database database statement-1 ...

     within-database creates a lexical scope in which the commands define-table and define-command create tables and *commands*-table entries respectively in open relational database DATABASE.

     within-database Returns DATABASE.

 -- Syntax: define-command (<name> <rdb>) "comment" <expression1> <expression2> ...
 -- Syntax: define-command (<name> <rdb>) <expression1> <expression2> ...

     Adds to the *commands* table a command <name>:

          (lambda (<name> <rdb>) <expression1> <expression2> ...)

 -- Syntax: define-table <name> <descriptor-name> <descriptor-name> <rows>
 -- Syntax: define-table <name> <primary-key-fields> <other-fields> <rows>

     where <name> is the table name, <descriptor-name> is the symbol name of a descriptor table, <primary-key-fields> and <other-fields> describe the primary keys and other fields respectively, and <rows> is a list of data rows to be added to the table.

     <primary-key-fields> and <other-fields> are lists of field descriptors of the form:

          (<column-name> <domain>)

     or

          (<column-name> <domain> <column-integrity-rule>)

     where <column-name> is the column name, <domain> is the domain of the column, and <column-integrity-rule> is an expression whose value is a procedure of one argument (which returns #f to signal an error).

     If <domain> is not a defined domain name and it matches the name of this table or an already defined (in one of SPEC-0 ...) single key field table, a foriegn-key domain will be created for it.

Within-database Example
.......................

Here is an example of within-database macros:

     (require 'within-database)

     (define my-rdb
       (add-command-tables
        (create-database "foo.db" 'alist-table)))

     (within-database my-rdb
       (define-command (*initialize* rdb)
         "Print Welcome"
         (display "Welcome")
         (newline)
         rdb)
       (define-table (processor-family
                      ((family   atom))
                      ((also-ran processor-family)))
         (m68000  #f)
         (m68030  m68000)
         (i386    8086)
         (8086    #f)
         (powerpc #f))
       (define-table (platform
                      ((name symbol))
                      ((processor processor-family)
                       (os        symbol)
                       (compiler  symbol)))
         (aix              powerpc aix     -)
         ;; ...
         (amiga-aztec      m68000  amiga   aztec)
         (amiga-sas/c-5.10 m68000  amiga   sas/c)
         (atari-st-gcc     m68000  atari   gcc)
         ;; ...
         (watcom-9.0       i386    ms-dos  watcom))
       (define-command (get-processor rdb)
         "Get processor for given platform."
         (((rdb 'open-table) 'platform #f) 'get 'processor)))

     ((my-rdb 'close-database))

     (set! my-rdb (open-command-database! "foo.db"))
     -|
     Welcome

     ((my-rdb 'get-processor) 'amiga-sas/c-5.10)
     => m68000

Database Reports
----------------

Code for generating database reports is in report.scm.  After writing it using format, I discovered that Common-Lisp format is not useable for this application because there is no mechanismm for truncating fields.  report.scm needs to be rewritten using printf.

 -- Procedure: create-report rdb destination report-name table
 -- Procedure: create-report rdb destination report-name
     The symbol REPORT-NAME must be primary key in the table named *reports* in the relational database RDB. DESTINATION is a port, string, or symbol.  If DESTINATION is a:

     port
          The table is created as ascii text and written to that port.

     string
          The table is created as ascii text and written to the file named by DESTINATION.

     symbol
          DESTINATION is the primary key for a row in the table named *printers*.

     The report is prepared as follows:

       * Format (see Format) is called with the header field and the (list of) column-names of the table.

       * Format is called with the reporter field and (on successive calls) each record in the natural order for the table.  A count is kept of the number of newlines output by format.  When the number of newlines to be output exceeds the number of lines per page, the set of lines will be broken if there are more than minimum-break left on this page and the number of lines for this row is larger or equal to twice minimum-break.

       * Format is called with the footer field and the (list of) column-names of the table.  The footer field should not output a newline.

       * A new page is output.

       * This entire process repeats until all the rows are output.

Each row in the table *reports* has the fields:

name
     The report name.

default-table
     The table to report on if none is specified.

header, footer
     A format string.  At the beginning and end of each page respectively, format is called with this string and the (list of) column-names of this table.

reporter
     A format string.  For each row in the table, format is called with this string and the row.

minimum-break
     The minimum number of lines into which the report lines for a row can be broken.  Use 0 if a row's lines should not be broken over page boundaries.

Each row in the table *printers* has the fields:

name
     The printer name.

print-procedure
     The procedure to call to actually print.

Database Browser
----------------

(require 'database-browse)

 -- Procedure: browse database

     Prints the names of all the tables in DATABASE and sets browse's default to DATABASE.

 -- Procedure: browse

     Prints the names of all the tables in the default database.

 -- Procedure: browse table-name

     For each record of the table named by the symbol TABLE-NAME, prints a line composed of all the field values.

 -- Procedure: browse pathname

     Opens the database named by the string PATHNAME, prints the names of all its tables, and sets browse's default to the database.

 -- Procedure: browse database table-name

     Sets browse's default to DATABASE and prints the records of the table named by the symbol TABLE-NAME.

 -- Procedure: browse pathname table-name

     Opens the database named by the string PATHNAME and sets browse's default to it; browse prints the records of the table named by the symbol TABLE-NAME.

Weight-Balanced Trees
=====================

(require 'wt-tree)

Balanced binary trees are a useful data structure for maintaining large sets of ordered objects or sets of associations whose keys are ordered. MIT Scheme has an comprehensive implementation of weight-balanced binary trees which has several advantages over the other data structures for large aggregates:

  * In addition to the usual element-level operations like insertion, deletion and lookup, there is a full complement of collection-level operations, like set intersection, set union and subset test, all of which are implemented with good orders of growth in time and space. This makes weight balanced trees ideal for rapid prototyping of functionally derived specifications.

  * An element in a tree may be indexed by its position under the ordering of the keys, and the ordinal position of an element may be determined, both with reasonable efficiency.

  * Operations to find and remove minimum element make weight balanced trees simple to use for priority queues.

  * The implementation is functional rather than imperative. This means that operations like `inserting' an association in a tree do not destroy the old tree, in much the same way that (+ 1 x) modifies neither the constant 1 nor the value bound to x.  The trees are referentially transparent thus the programmer need not worry about copying the trees.  Referential transparency allows space efficiency to be achieved by sharing subtrees.

These features make weight-balanced trees suitable for a wide range of applications, especially those that require large numbers of sets or discrete maps.  Applications that have a few global databases and/or concentrate on element-level operations like insertion and lookup are probably better off using hash-tables or red-black trees.

The size of a tree is the number of associations that it contains.  Weight balanced binary trees are balanced to keep the sizes of the subtrees of each node within a constant factor of each other. This ensures logarithmic times for single-path operations (like lookup and insertion).  A weight balanced tree takes space that is proportional to the number of associations in the tree.  For the current implementation, the constant of proportionality is six words per association.

Weight balanced trees can be used as an implementation for either discrete sets or discrete maps (associations).  Sets are implemented by ignoring the datum that is associated with the key.  Under this scheme if an associations exists in the tree this indicates that the key of the association is a member of the set.  Typically a value such as (), #t or #f is associated with the key.

Many operations can be viewed as computing a result that, depending on whether the tree arguments are thought of as sets or maps, is known by two different names.  An example is wt-tree/member?, which, when regarding the tree argument as a set, computes the set membership operation, but, when regarding the tree as a discrete map, wt-tree/member? is the predicate testing if the map is defined at an element in its domain.  Most names in this package have been chosen based on interpreting the trees as sets, hence the name wt-tree/member? rather than wt-tree/defined-at?.

The weight balanced tree implementation is a run-time-loadable option. To use weight balanced trees, execute

     (load-option 'wt-tree)

once before calling any of the procedures defined here.

Construction of Weight-Balanced Trees
-------------------------------------

Binary trees require there to be a total order on the keys used to arrange the elements in the tree.  Weight balanced trees are organized by types, where the type is an object encapsulating the ordering relation.  Creating a tree is a two-stage process.  First a tree type must be created from the predicate which gives the ordering.  The tree type is then used for making trees, either empty or singleton trees or trees from other aggregate structures like association lists.  Once created, a tree `knows' its type and the type is used to test compatibility between trees in operations taking two trees.  Usually a small number of tree types are created at the beginning of a program and used many times throughout the program's execution.

 -- procedure+: make-wt-tree-type key<?
     This procedure creates and returns a new tree type based on the ordering predicate KEY<?. KEY<? must be a total ordering, having the property that for all key values a, b and c:

          (key<? a a)                         => #f
          (and (key<? a b) (key<? b a))       => #f
          (if (and (key<? a b) (key<? b c))
              (key<? a c)
              #t)                             => #t

     Two key values are assumed to be equal if neither is less than the other by KEY<?.

     Each call to make-wt-tree-type returns a distinct value, and trees are only compatible if their tree types are eq?.  A consequence is that trees that are intended to be used in binary tree operations must all be created with a tree type originating from the same call to make-wt-tree-type.

 -- variable+: number-wt-type
     A standard tree type for trees with numeric keys.  Number-wt-type could have been defined by

          (define number-wt-type (make-wt-tree-type  <))

 -- variable+: string-wt-type
     A standard tree type for trees with string keys.  String-wt-type could have been defined by

          (define string-wt-type (make-wt-tree-type  string<?))

 -- procedure+: make-wt-tree wt-tree-type
     This procedure creates and returns a newly allocated weight balanced tree.  The tree is empty, i.e. it contains no associations. WT-TREE-TYPE is a weight balanced tree type obtained by calling make-wt-tree-type; the returned tree has this type.

 -- procedure+: singleton-wt-tree wt-tree-type key datum
     This procedure creates and returns a newly allocated weight balanced tree.  The tree contains a single association, that of DATUM with KEY.  WT-TREE-TYPE is a weight balanced tree type obtained by calling make-wt-tree-type; the returned tree has this type.

 -- procedure+: alist->wt-tree tree-type alist
     Returns a newly allocated weight-balanced tree that contains the same associations as ALIST.  This procedure is equivalent to:

          (lambda (type alist)
            (let ((tree (make-wt-tree type)))
              (for-each (lambda (association)
                          (wt-tree/add! tree
                                        (car association)
                                        (cdr association)))
                        alist)
              tree))

Basic Operations on Weight-Balanced Trees
-----------------------------------------

This section describes the basic tree operations on weight balanced trees.  These operations are the usual tree operations for insertion, deletion and lookup, some predicates and a procedure for determining the number of associations in a tree.

 -- procedure+: wt-tree? object
     Returns #t if OBJECT is a weight-balanced tree, otherwise returns #f.

 -- procedure+: wt-tree/empty? wt-tree
     Returns #t if WT-TREE contains no associations, otherwise returns #f.

 -- procedure+: wt-tree/size wt-tree
     Returns the number of associations in WT-TREE, an exact non-negative integer.  This operation takes constant time.

 -- procedure+: wt-tree/add wt-tree key datum
     Returns a new tree containing all the associations in WT-TREE and the association of DATUM with KEY.  If WT-TREE already had an association for KEY, the new association overrides the old. The average and worst-case times required by this operation are proportional to the logarithm of the number of associations in WT-TREE.

 -- procedure+: wt-tree/add! wt-tree key datum
     Associates DATUM with KEY in WT-TREE and returns an unspecified value.  If WT-TREE already has an association for KEY, that association is replaced.  The average and worst-case times required by this operation are proportional to the logarithm of the number of associations in WT-TREE.

 -- procedure+: wt-tree/member? key wt-tree
     Returns #t if WT-TREE contains an association for KEY, otherwise returns #f.  The average and worst-case times required by this operation are proportional to the logarithm of the number of associations in WT-TREE.

 -- procedure+: wt-tree/lookup wt-tree key default
     Returns the datum associated with KEY in WT-TREE.  If WT-TREE doesn't contain an association for KEY, DEFAULT is returned.  The average and worst-case times required by this operation are proportional to the logarithm of the number of associations in WT-TREE.

 -- procedure+: wt-tree/delete wt-tree key
     Returns a new tree containing all the associations in WT-TREE, except that if WT-TREE contains an association for KEY, it is removed from the result.  The average and worst-case times required by this operation are proportional to the logarithm of the number of associations in WT-TREE.

 -- procedure+: wt-tree/delete! wt-tree key
     If WT-TREE contains an association for KEY the association is removed.  Returns an unspecified value.  The average and worst-case times required by this operation are proportional to the logarithm of the number of associations in WT-TREE.

Advanced Operations on Weight-Balanced Trees
--------------------------------------------

In the following the size of a tree is the number of associations that the tree contains, and a smaller tree contains fewer associations.

 -- procedure+: wt-tree/split< wt-tree bound
     Returns a new tree containing all and only the associations in WT-TREE which have a key that is less than BOUND in the ordering relation of the tree type of WT-TREE.  The average and worst-case times required by this operation are proportional to the logarithm of the size of WT-TREE.

 -- procedure+: wt-tree/split> wt-tree bound
     Returns a new tree containing all and only the associations in WT-TREE which have a key that is greater than BOUND in the ordering relation of the tree type of WT-TREE.  The average and worst-case times required by this operation are proportional to the logarithm of size of WT-TREE.

 -- procedure+: wt-tree/union wt-tree-1 wt-tree-2
     Returns a new tree containing all the associations from both trees. This operation is asymmetric: when both trees have an association for the same key, the returned tree associates the datum from WT-TREE-2 with the key.  Thus if the trees are viewed as discrete maps then wt-tree/union computes the map override of WT-TREE-1 by WT-TREE-2.  If the trees are viewed as sets the result is the set union of the arguments. The worst-case time required by this operation is proportional to the sum of the sizes of both trees. If the minimum key of one tree is greater than the maximum key of the other tree then the time required is at worst proportional to the logarithm of the size of the larger tree.

 -- procedure+: wt-tree/intersection wt-tree-1 wt-tree-2
     Returns a new tree containing all and only those associations from WT-TREE-1 which have keys appearing as the key of an association in WT-TREE-2.  Thus the associated data in the result are those from WT-TREE-1.  If the trees are being used as sets the result is the set intersection of the arguments.  As a discrete map operation, wt-tree/intersection computes the domain restriction of WT-TREE-1 to (the domain of) WT-TREE-2. The time required by this operation is never worse that proportional to the sum of the sizes of the trees.

 -- procedure+: wt-tree/difference wt-tree-1 wt-tree-2
     Returns a new tree containing all and only those associations from WT-TREE-1 which have keys that do not appear as the key of an association in WT-TREE-2.  If the trees are viewed as sets the result is the asymmetric set difference of the arguments.  As a discrete map operation, it computes the domain restriction of WT-TREE-1 to the complement of (the domain of) WT-TREE-2. The time required by this operation is never worse that proportional to the sum of the sizes of the trees.

 -- procedure+: wt-tree/subset? wt-tree-1 wt-tree-2
     Returns #t iff the key of each association in WT-TREE-1 is the key of some association in WT-TREE-2, otherwise returns #f. Viewed as a set operation, wt-tree/subset? is the improper subset predicate. A proper subset predicate can be constructed:

          (define (proper-subset? s1 s2)
            (and (wt-tree/subset? s1 s2)
                 (< (wt-tree/size s1) (wt-tree/size s2))))

     As a discrete map operation, wt-tree/subset? is the subset test on the domain(s) of the map(s).  In the worst-case the time required by this operation is proportional to the size of WT-TREE-1.

 -- procedure+: wt-tree/set-equal? wt-tree-1 wt-tree-2
     Returns #t iff for every association in WT-TREE-1 there is an association in WT-TREE-2 that has the same key, and vice versa.

     Viewing the arguments as sets wt-tree/set-equal? is the set equality predicate.  As a map operation it determines if two maps are defined on the same domain.

     This procedure is equivalent to

          (lambda (wt-tree-1 wt-tree-2)
            (and (wt-tree/subset? wt-tree-1 wt-tree-2
                 (wt-tree/subset? wt-tree-2 wt-tree-1)))

     In the worst-case the time required by this operation is proportional to the size of the smaller tree.

 -- procedure+: wt-tree/fold combiner initial wt-tree
     This procedure reduces WT-TREE by combining all the associations, using an reverse in-order traversal, so the associations are visited in reverse order.  COMBINER is a procedure of three arguments: a key, a datum and the accumulated result so far.  Provided COMBINER takes time bounded by a constant, wt-tree/fold takes time proportional to the size of WT-TREE.

     A sorted association list can be derived simply:

          (wt-tree/fold  (lambda (key datum list)
                           (cons (cons key datum) list))
                         '()
                         WT-TREE))

     The data in the associations can be summed like this:

          (wt-tree/fold  (lambda (key datum sum) (+ sum datum))
                         0
                         WT-TREE)

 -- procedure+: wt-tree/for-each action wt-tree
     This procedure traverses the tree in-order, applying ACTION to each association. The associations are processed in increasing order of their keys. ACTION is a procedure of two arguments which take the key and datum respectively of the association. Provided ACTION takes time bounded by a constant, wt-tree/for-each takes time proportional to in the size of WT-TREE. The example prints the tree:

          (wt-tree/for-each (lambda (key value)
                              (display (list key value)))
                            WT-TREE))

Indexing Operations on Weight-Balanced Trees
--------------------------------------------

Weight balanced trees support operations that view the tree as sorted sequence of associations.  Elements of the sequence can be accessed by position, and the position of an element in the sequence can be determined, both in logarthmic time.

 -- procedure+: wt-tree/index wt-tree index
 -- procedure+: wt-tree/index-datum wt-tree index
 -- procedure+: wt-tree/index-pair wt-tree index
     Returns the 0-based INDEXth association of WT-TREE in the sorted sequence under the tree's ordering relation on the keys. wt-tree/index returns the INDEXth key, wt-tree/index-datum returns the datum associated with the INDEXth key and wt-tree/index-pair returns a new pair (KEY . DATUM) which is the cons of the INDEXth key and its datum.  The average and worst-case times required by this operation are proportional to the logarithm of the number of associations in the tree.

     These operations signal an error if the tree is empty, if INDEX<0, or if INDEX is greater than or equal to the number of associations in the tree.

     Indexing can be used to find the median and maximum keys in the tree as follows:

          median:   (wt-tree/index WT-TREE
                                   (quotient (wt-tree/size WT-TREE) 2))

          maximum:  (wt-tree/index WT-TREE
                                   (-1+ (wt-tree/size WT-TREE)))

 -- procedure+: wt-tree/rank wt-tree key
     Determines the 0-based position of KEY in the sorted sequence of the keys under the tree's ordering relation, or #f if the tree has no association with for KEY.  This procedure returns either an exact non-negative integer or #f.  The average and worst-case times required by this operation are proportional to the logarithm of the number of associations in the tree.

 -- procedure+: wt-tree/min wt-tree
 -- procedure+: wt-tree/min-datum wt-tree
 -- procedure+: wt-tree/min-pair wt-tree
     Returns the association of WT-TREE that has the least key under the tree's ordering relation.  wt-tree/min returns the least key, wt-tree/min-datum returns the datum associated with the least key and wt-tree/min-pair returns a new pair (key . datum) which is the cons of the minimum key and its datum.  The average and worst-case times required by this operation are proportional to the logarithm of the number of associations in the tree.

     These operations signal an error if the tree is empty. They could be written

          (define (wt-tree/min tree)        (wt-tree/index tree 0))
          (define (wt-tree/min-datum tree)  (wt-tree/index-datum tree 0))
          (define (wt-tree/min-pair tree)   (wt-tree/index-pair tree 0))

 -- procedure+: wt-tree/delete-min wt-tree
     Returns a new tree containing all of the associations in WT-TREE except the association with the least key under the WT-TREE's ordering relation.  An error is signalled if the tree is empty.  The average and worst-case times required by this operation are proportional to the logarithm of the number of associations in the tree.  This operation is equivalent to

          (wt-tree/delete WT-TREE (wt-tree/min WT-TREE))

 -- procedure+: wt-tree/delete-min! wt-tree
     Removes the association with the least key under the WT-TREE's ordering relation.  An error is signalled if the tree is empty.  The average and worst-case times required by this operation are proportional to the logarithm of the number of associations in the tree.  This operation is equivalent to

          (wt-tree/delete! WT-TREE (wt-tree/min WT-TREE))

Other Packages
**************

Data Structures
===============

Arrays
------

     [file array.txi not included]

Subarrays
---------

     [file subarray.txi not included]

Array Mapping
-------------

(require 'array-for-each)

 -- Function: array-map! array0 proc array1 ...
     ARRAY1, ... must have the same number of dimensions as ARRAY0 and have a range for each index which includes the range for the corresponding index in ARRAY0.  PROC is applied to each tuple of elements of ARRAY1 ... and the result is stored as the corresponding element in ARRAY0.  The value returned is unspecified.  The order of application is unspecified.

 -- Function: array-for-each PROC ARRAY0 ...
     PROC is applied to each tuple of elements of ARRAY0 ... in row-major order.  The value returned is unspecified.

 -- Function: array-indexes ARRAY
     Returns an array of lists of indexes for ARRAY such that, if LI is a list of indexes for which ARRAY is defined, (equal? LI (apply array-ref (array-indexes ARRAY) LI)).

 -- Function: array-index-map! array proc
     applies PROC to the indices of each element of ARRAY in turn, storing the result in the corresponding element.  The value returned and the order of application are unspecified.

     One can implement ARRAY-INDEXES as

          (define (array-indexes array)
              (let ((ra (apply create-array '#() (array-shape array))))
                (array-index-map! ra (lambda x x))
                ra))

     Another example:

          (define (apl:index-generator n)
              (let ((v (make-vector n 1)))
                (array-index-map! v (lambda (i) i))
                v))

 -- Function: array-copy! source destination
     Copies every element from vector or array SOURCE to the corresponding element of DESTINATION.  DESTINATION must have the same rank as SOURCE, and be at least as large in each dimension.  The order of copying is unspecified.

Association Lists
-----------------

(require 'alist)

Alist functions provide utilities for treating a list of key-value pairs as an associative database.  These functions take an equality predicate, PRED, as an argument.  This predicate should be repeatable, symmetric, and transitive.

Alist functions can be used with a secondary index method such as hash tables for improved performance.

 -- Function: predicate->asso pred
     Returns an association function (like assq, assv, or assoc) corresponding to PRED.  The returned function returns a key-value pair whose key is pred-equal to its first argument or #f if no key in the alist is PRED-equal to the first argument.

 -- Function: alist-inquirer pred
     Returns a procedure of 2 arguments, ALIST and KEY, which returns the value associated with KEY in ALIST or #f if KEY does not appear in ALIST.

 -- Function: alist-associator pred
     Returns a procedure of 3 arguments, ALIST, KEY, and VALUE, which returns an alist with KEY and VALUE associated.  Any previous value associated with KEY will be lost.  This returned procedure may or may not have side effects on its ALIST argument.  An example of correct usage is:

          (define put (alist-associator string-ci=?))
          (define alist '())
          (set! alist (put alist "Foo" 9))

 -- Function: alist-remover pred
     Returns a procedure of 2 arguments, ALIST and KEY, which returns an alist with an association whose KEY is key removed. This returned procedure may or may not have side effects on its ALIST argument.  An example of correct usage is:

          (define rem (alist-remover string-ci=?))
          (set! alist (rem alist "foo"))

 -- Function: alist-map proc alist
     Returns a new association list formed by mapping PROC over the keys and values of ALIST.   PROC must be a function of 2 arguments which returns the new value part.

 -- Function: alist-for-each proc alist
     Applies PROC to each pair of keys and values of ALIST. PROC must be a function of 2 arguments.  The returned value is unspecified.

Byte
----

(require 'byte)

Some algorithms are expressed in terms of arrays of small integers. Using Scheme strings to implement these arrays is not portable vis-a-vis the correspondence between integers and characters and non-ascii character sets.  These functions abstract the notion of a byte.

 -- Function: byte-ref bytes k
     K must be a valid index of BYTES.  byte-ref returns byte K of BYTES using zero-origin indexing.

 -- Procedure: byte-set! bytes k byte
     K must be a valid index of BYTES%, and BYTE must be a small integer.  Byte-set! stores BYTE in element K of BYTES and returns an unspecified value.

 -- Function: make-bytes k
 -- Function: make-bytes k byte

     Make-bytes returns a newly allocated byte-array of length K.  If BYTE is given, then all elements of the byte-array are initialized to BYTE, otherwise the contents of the byte-array are unspecified.

 -- Function: bytes-length bytes

     bytes-length returns length of byte-array BYTES.

 -- Function: bytes byte ...

     Returns a newly allocated byte-array composed of the arguments.

 -- Function: bytes->list bytes
 -- Function: list->bytes bytes

     Bytes->list returns a newly allocated list of the bytes that make up the given byte-array.  List->bytes returns a newly allocated byte-array formed from the small integers in the list BYTES. Bytes->list and list->bytes are inverses so far as equal? is concerned.

Input and output of bytes should be with ports opened in binary mode (see Input/Output).  Calling open-file with 'rb or 'wb modes argument will return a binary port if the Scheme implementation supports it.

 -- Function: write-byte byte
 -- Function: write-byte byte port

     Writes the byte BYTE (not an external representation of the byte) to the given PORT and returns an unspecified value.  The PORT argument may be omitted, in which case it defaults to the value returned by current-output-port.

 -- Function: read-byte
 -- Function: read-byte port

     Returns the next byte available from the input PORT, updating the PORT to point to the following byte.  If no more bytes are available, an end of file object is returned.  PORT may be omitted, in which case it defaults to the value returned by current-input-port.

MAT-File Format
---------------

     [file matfile.txi not included]

Portable Image Files
--------------------

(require 'pnm)

 -- Function: pnm:type-dimensions path
     The string PATH must name a portable bitmap graphics file. pnm:type-dimensions returns a list of 4 items:

      1. A symbol describing the type of the file named by PATH.

      2. The image width in pixels.

      3. The image height in pixels.

      4. The maximum value of pixels assume in the file.

     The current set of file-type symbols is:

     pbm
     pbm-raw
          Black-and-White image; pixel values are 0 or 1.

     pgm
     pgm-raw
          Gray (monochrome) image; pixel values are from 0 to MAXVAL specified in file header.

     ppm
     ppm-raw
          RGB (full color) image; red, green, and blue interleaved pixel values are from 0 to MAXVAL

 -- Function: pnm:image-file->array path array

     Reads the portable bitmap graphics file named by PATH into ARRAY.  ARRAY must be the correct size and type for PATH.  ARRAY is returned.

 -- Function: pnm:image-file->array path

     pnm:image-file->array creates and returns an array with the portable bitmap graphics file named by PATH read into it.

 -- Procedure: pnm:array-write type array maxval path comment ...

     Writes the contents of ARRAY to a TYPE image file named PATH.  The file will have pixel values between 0 and MAXVAL, which must be compatible with TYPE.  For pbm files, MAXVAL must be 1.  COMMENTs are included in the file header.

Collections
-----------

(require 'collect)

Routines for managing collections.  Collections are aggregate data structures supporting iteration over their elements, similar to the Dylan(TM) language, but with a different interface.  They have elements indexed by corresponding keys, although the keys may be implicit (as with lists).

New types of collections may be defined as YASOS objects (see Yasos). They must support the following operations:

  * (collection? SELF) (always returns #t);

  * (size SELF) returns the number of elements in the collection;

  * (print SELF PORT) is a specialized print operation for the collection which prints a suitable representation on the given PORT or returns it as a string if PORT is #t;

  * (gen-elts SELF) returns a thunk which on successive invocations yields elements of SELF in order or gives an error if it is invoked more than (size SELF) times;

  * (gen-keys SELF) is like gen-elts, but yields the collection's keys in order.

They might support specialized for-each-key and for-each-elt operations.

 -- Function: collection? obj
     A predicate, true initially of lists, vectors and strings.  New sorts of collections must answer #t to collection?.

 -- Procedure: map-elts proc collection1 ...
 -- Procedure: do-elts proc collection1 ...
     PROC is a procedure taking as many arguments as there are COLLECTIONS (at least one).  The COLLECTIONS are iterated over in their natural order and PROC is applied to the elements yielded by each iteration in turn.  The order in which the arguments are supplied corresponds to te order in which the COLLECTIONS appear. do-elts is used when only side-effects of PROC are of interest and its return value is unspecified.  map-elts returns a collection (actually a vector) of the results of the applications of PROC.

     Example:

          (map-elts + (list 1 2 3) (vector 1 2 3))
             => #(2 4 6)

 -- Procedure: map-keys proc collection1 ...
 -- Procedure: do-keys proc collection1 ...
     These are analogous to map-elts and do-elts, but each iteration is over the COLLECTIONS' keys rather than their elements.

     Example:

          (map-keys + (list 1 2 3) (vector 1 2 3))
             => #(0 2 4)

 -- Procedure: for-each-key collection proc
 -- Procedure: for-each-elt collection proc
     These are like do-keys and do-elts but only for a single collection; they are potentially more efficient.

 -- Function: reduce proc seed collection1 ...
     A generalization of the list-based comlist:reduce-init (see Lists as sequences) to collections which will shadow the list-based version if (require 'collect) follows (require 'common-list-functions) (see Common List Functions).

     Examples:

          (reduce + 0 (vector 1 2 3))
             => 6
          (reduce union '() '((a b c) (b c d) (d a)))
             => (c b d a).

 -- Function: any? pred collection1 ...
     A generalization of the list-based some (see Lists as sequences) to collections.

     Example:

          (any? odd? (list 2 3 4 5))
             => #t

 -- Function: every? pred collection1 ...
     A generalization of the list-based every (see Lists as sequences) to collections.

     Example:

          (every? collection? '((1 2) #(1 2)))
             => #t

 -- Function: empty? collection
     Returns #t iff there are no elements in COLLECTION.

     (empty? COLLECTION) == (zero? (size COLLECTION))

 -- Function: size collection
     Returns the number of elements in COLLECTION.

 -- Function: Setter list-ref
     See Setters for a definition of setter.  N.B. (setter list-ref) doesn't work properly for element 0 of a list.

Here is a sample collection: simple-table which is also a table.

     (define-predicate TABLE?)
     (define-operation (LOOKUP table key failure-object))
     (define-operation (ASSOCIATE! table key value)) ;; returns key
     (define-operation (REMOVE! table key))          ;; returns value

     (define (MAKE-SIMPLE-TABLE)
       (let ( (table (list)) )
         (object
          ;; table behaviors
          ((TABLE? self) #t)
          ((SIZE self) (size table))
          ((PRINT self port) (format port "#<SIMPLE-TABLE>"))
          ((LOOKUP self key failure-object)
           (cond
            ((assq key table) => cdr)
            (else failure-object)
            ))
          ((ASSOCIATE! self key value)
           (cond
            ((assq key table)
             => (lambda (bucket) (set-cdr! bucket value) key))
            (else
             (set! table (cons (cons key value) table))
             key)
            ))
          ((REMOVE! self key);; returns old value
           (cond
            ((null? table) (slib:error "TABLE:REMOVE! Key not found: " key))
            ((eq? key (caar table))
             (let ( (value (cdar table)) )
               (set! table (cdr table))
               value)
             )
            (else
             (let loop ( (last table) (this (cdr table)) )
               (cond
                ((null? this)
                 (slib:error "TABLE:REMOVE! Key not found: " key))
                ((eq? key (caar this))
                 (let ( (value (cdar this)) )
                   (set-cdr! last (cdr this))
                   value)
                 )
                (else
                 (loop (cdr last) (cdr this)))
                ) ) )
            ))
          ;; collection behaviors
          ((COLLECTION? self) #t)
          ((GEN-KEYS self) (collect:list-gen-elts (map car table)))
          ((GEN-ELTS self) (collect:list-gen-elts (map cdr table)))
          ((FOR-EACH-KEY self proc)
           (for-each (lambda (bucket) (proc (car bucket))) table)
           )
          ((FOR-EACH-ELT self proc)
           (for-each (lambda (bucket) (proc (cdr bucket))) table)
           )
          ) ) )

Dynamic Data Type
-----------------

(require 'dynamic)

 -- Function: make-dynamic obj
     Create and returns a new dynamic whose global value is OBJ.

 -- Function: dynamic? obj
     Returns true if and only if OBJ is a dynamic.  No object satisfying dynamic? satisfies any of the other standard type predicates.

 -- Function: dynamic-ref dyn
     Return the value of the given dynamic in the current dynamic environment.

 -- Procedure: dynamic-set! dyn obj
     Change the value of the given dynamic to OBJ in the current dynamic environment.  The returned value is unspecified.

 -- Function: call-with-dynamic-binding dyn obj thunk
     Invoke and return the value of the given thunk in a new, nested dynamic environment in which the given dynamic has been bound to a new location whose initial contents are the value OBJ.  This dynamic environment has precisely the same extent as the invocation of the thunk and is thus captured by continuations created within that invocation and re-established by those continuations when they are invoked.

The dynamic-bind macro is not implemented.

Hash Tables
-----------

(require 'hash-table)

 -- Function: predicate->hash pred
     Returns a hash function (like hashq, hashv, or hash) corresponding to the equality predicate PRED. PRED should be eq?, eqv?, equal?, =, char=?, char-ci=?, string=?, or string-ci=?.

A hash table is a vector of association lists.

 -- Function: make-hash-table k
     Returns a vector of K empty (association) lists.

Hash table functions provide utilities for an associative database. These functions take an equality predicate, PRED, as an argument. PRED should be eq?, eqv?, equal?, =, char=?, char-ci=?, string=?, or string-ci=?.

 -- Function: predicate->hash-asso pred
     Returns a hash association function of 2 arguments, KEY and HASHTAB, corresponding to PRED.  The returned function returns a key-value pair whose key is PRED-equal to its first argument or #f if no key in HASHTAB is PRED-equal to the first argument.

 -- Function: hash-inquirer pred
     Returns a procedure of 2 arguments, HASHTAB and KEY, which returns the value associated with KEY in HASHTAB or #f if KEY does not appear in HASHTAB.

 -- Function: hash-associator pred
     Returns a procedure of 3 arguments, HASHTAB, KEY, and VALUE, which modifies HASHTAB so that KEY and VALUE associated.  Any previous value associated with KEY will be lost.

 -- Function: hash-remover pred
     Returns a procedure of 2 arguments, HASHTAB and KEY, which modifies HASHTAB so that the association whose key is KEY is removed.

 -- Function: hash-map proc hash-table
     Returns a new hash table formed by mapping PROC over the keys and values of HASH-TABLE.  PROC must be a function of 2 arguments which returns the new value part.

 -- Function: hash-for-each proc hash-table
     Applies PROC to each pair of keys and values of HASH-TABLE. PROC must be a function of 2 arguments.  The returned value is unspecified.

Macroless Object System
-----------------------

     [file objdoc.txi not included]

Priority Queues
---------------

(require 'priority-queue)

 -- Function: make-heap pred<?
     Returns a binary heap suitable which can be used for priority queue operations.

 -- Function: heap-length heap
     Returns the number of elements in HEAP.

 -- Procedure: heap-insert! heap item
     Inserts ITEM into HEAP.  ITEM can be inserted multiple times.  The value returned is unspecified.

 -- Function: heap-extract-max! heap
     Returns the item which is larger than all others according to the PRED<? argument to make-heap.  If there are no items in HEAP, an error is signaled.

The algorithm for priority queues was taken from Introduction to Algorithms by T. Cormen, C. Leiserson, R. Rivest.  1989 MIT Press.

Queues
------

(require 'queue)

A queue is a list where elements can be added to both the front and rear, and removed from the front (i.e., they are what are often called dequeues).  A queue may also be used like a stack.

 -- Function: make-queue
     Returns a new, empty queue.

 -- Function: queue? obj
     Returns #t if OBJ is a queue.

 -- Function: queue-empty? q
     Returns #t if the queue Q is empty.

 -- Procedure: queue-push! q datum
     Adds DATUM to the front of queue Q.

 -- Procedure: enquque! q datum
     Adds DATUM to the rear of queue Q.

All of the following functions raise an error if the queue Q is empty.

 -- Function: queue-front q
     Returns the datum at the front of the queue Q.

 -- Function: queue-rear q
     Returns the datum at the rear of the queue Q.

 -- Prcoedure: queue-pop! q
 -- Procedure: dequeue! q
     Both of these procedures remove and return the datum at the front of the queue.  queue-pop! is used to suggest that the queue is being used like a stack.

Records
-------

(require 'record)

The Record package provides a facility for user to define their own record data types.

 -- Function: make-record-type type-name field-names
     Returns a record-type descriptor, a value representing a new data type disjoint from all others.  The TYPE-NAME argument must be a string, but is only used for debugging purposes (such as the printed representation of a record of the new type).  The FIELD-NAMES argument is a list of symbols naming the fields of a record of the new type.  It is an error if the list contains any duplicates.  It is unspecified how record-type descriptors are represented.

 -- Function: record-constructor rtd [field-names]
     Returns a procedure for constructing new members of the type represented by RTD.  The returned procedure accepts exactly as many arguments as there are symbols in the given list, FIELD-NAMES; these are used, in order, as the initial values of those fields in a new record, which is returned by the constructor procedure.  The values of any fields not named in that list are unspecified.  The FIELD-NAMES argument defaults to the list of field names in the call to make-record-type that created the type represented by RTD; if the FIELD-NAMES argument is provided, it is an error if it contains any duplicates or any symbols not in the default list.

 -- Function: record-predicate rtd
     Returns a procedure for testing membership in the type represented by RTD.  The returned procedure accepts exactly one argument and returns a true value if the argument is a member of the indicated record type; it returns a false value otherwise.

 -- Function: record-accessor rtd field-name
     Returns a procedure for reading the value of a particular field of a member of the type represented by RTD.  The returned procedure accepts exactly one argument which must be a record of the appropriate type; it returns the current value of the field named by the symbol FIELD-NAME in that record.  The symbol FIELD-NAME must be a member of the list of field-names in the call to make-record-type that created the type represented by RTD.

 -- Function: record-modifier rtd field-name
     Returns a procedure for writing the value of a particular field of a member of the type represented by RTD.  The returned procedure accepts exactly two arguments: first, a record of the appropriate type, and second, an arbitrary Scheme value; it modifies the field named by the symbol FIELD-NAME in that record to contain the given value. The returned value of the modifier procedure is unspecified.  The symbol FIELD-NAME must be a member of the list of field-names in the call to make-record-type that created the type represented by RTD.

In May of 1996, as a product of discussion on the rrrs-authors mailing list, I rewrote record.scm to portably implement type disjointness for record data types.

As long as an implementation's procedures are opaque and the record code is loaded before other programs, this will give disjoint record types which are unforgeable and incorruptible by R4RS procedures.

As a consequence, the procedures record?, record-type-descriptor, record-type-name.and record-type-field-names are no longer supported.

Sorting and Searching
=====================

Common List Functions
---------------------

(require 'common-list-functions)

The procedures below follow the Common LISP equivalents apart from optional arguments in some cases.

List construction
.................

 -- Function: make-list k
 -- Function: make-list k init
     make-list creates and returns a list of K elements.  If INIT is included, all elements in the list are initialized to INIT.

     Example:

          (make-list 3)
             => (#<unspecified> #<unspecified> #<unspecified>)
          (make-list 5 'foo)
             => (foo foo foo foo foo)

 -- Function: list* obj1 obj2 ...
     Works like list except that the cdr of the last pair is the last argument unless there is only one argument, when the result is just that argument.  Sometimes called cons*.  E.g.:

          (list* 1)
             => 1
          (list* 1 2 3)
             => (1 2 . 3)
          (list* 1 2 '(3 4))
             => (1 2 3 4)
          (list* ARGS '())
             == (list ARGS)

 -- Function: copy-list lst
     copy-list makes a copy of LST using new pairs and returns it. Only the top level of the list is copied, i.e., pairs forming elements of the copied list remain eq? to the corresponding elements of the original; the copy is, however, not eq? to the original, but is equal? to it.

     Example:

          (copy-list '(foo foo foo))
             => (foo foo foo)
          (define q '(foo bar baz bang))
          (define p q)
          (eq? p q)
             => #t
          (define r (copy-list q))
          (eq? q r)
             => #f
          (equal? q r)
             => #t
          (define bar '(bar))
          (eq? bar (car (copy-list (list bar 'foo))))
          => #t

Lists as sets
.............

eqv? is used to test for membership by procedures which treat lists as sets.

 -- Function: adjoin e l
     adjoin returns the adjoint of the element E and the list L.  That is, if E is in L, adjoin returns L, otherwise, it returns (cons E L).

     Example:

          (adjoin 'baz '(bar baz bang))
             => (bar baz bang)
          (adjoin 'foo '(bar baz bang))
             => (foo bar baz bang)

 -- Function: union l1 l2
     union returns the combination of L1 and L2. Duplicates between L1 and L2 are culled.  Duplicates within L1 or within L2 may or may not be removed.

     Example:

          (union '(1 2 3 4) '(5 6 7 8))
             => (8 7 6 5 1 2 3 4)
          (union '(1 2 3 4) '(3 4 5 6))
             => (6 5 1 2 3 4)

 -- Function: intersection l1 l2
     intersection returns all elements that are in both L1 and L2.

     Example:

          (intersection '(1 2 3 4) '(3 4 5 6))
             => (3 4)
          (intersection '(1 2 3 4) '(5 6 7 8))
             => ()

 -- Function: set-difference l1 l2
     set-difference returns all elements that are in L1 but not in L2.

     Example:

          (set-difference '(1 2 3 4) '(3 4 5 6))
             => (1 2)
          (set-difference '(1 2 3 4) '(1 2 3 4 5 6))
             => ()

 -- Function: member-if pred lst
     member-if returns the list headed by the first element of LST to satisfy (PRED ELEMENT). Member-if returns #f if PRED returns #f for every ELEMENT in LST.

     Example:

          (member-if vector? '(a 2 b 4))
             => #f
          (member-if number? '(a 2 b 4))
             => (2 b 4)

 -- Function: some pred lst1 lst2 ...
     PRED is a boolean function of as many arguments as there are list arguments to some i.e., LST plus any optional arguments. PRED is applied to successive elements of the list arguments in order.  some returns #t as soon as one of these applications returns #t, and is #f if none returns #t.  All the lists should have the same length.

     Example:

          (some odd? '(1 2 3 4))
             => #t

          (some odd? '(2 4 6 8))
             => #f

          (some > '(2 3) '(1 4))
             => #f

 -- Function: every pred lst1 lst2 ...
     every is analogous to some except it returns #t if every application of PRED is #t and #f otherwise.

     Example:

          (every even? '(1 2 3 4))
             => #f

          (every even? '(2 4 6 8))
             => #t

          (every > '(2 3) '(1 4))
             => #f

 -- Function: notany pred lst1 ...
     notany is analogous to some but returns #t if no application of PRED returns #t or #f as soon as any one does.

 -- Function: notevery pred lst1 ...
     notevery is analogous to some but returns #t as soon as an application of PRED returns #f, and #f otherwise.

     Example:

          (notevery even? '(1 2 3 4))
             => #t

          (notevery even? '(2 4 6 8))
             => #f

 -- Function: list-of?? predicate
     Returns a predicate which returns true if its argument is a list every element of which satisfies PREDICATE.

 -- Function: list-of?? predicate low-bound high-bound
     LOW-BOUND and HIGH-BOUND are non-negative integers. list-of?? returns a predicate which returns true if its argument is a list of length between LOW-BOUND and HIGH-BOUND (inclusive); every element of which satisfies PREDICATE.

 -- Function: list-of?? predicate bound
     BOUND is an integer.  If BOUND is negative, list-of?? returns a predicate which returns true if its argument is a list of length greater than (- BOUND); every element of which satisfies PREDICATE.  Otherwise, list-of??  returns a predicate which returns true if its argument is a list of length less than or equal to BOUND; every element of which satisfies PREDICATE.

 -- Function: find-if pred lst
     find-if searches for the first ELEMENT in LST such that (PRED ELEMENT) returns #t.  If it finds any such ELEMENT in LST, ELEMENT is returned. Otherwise, #f is returned.

     Example:

          (find-if number? '(foo 1 bar 2))
             => 1

          (find-if number? '(foo bar baz bang))
             => #f

          (find-if symbol? '(1 2 foo bar))
             => foo

 -- Function: remove elt lst
     remove removes all occurrences of ELT from LST using eqv? to test for equality and returns everything that's left. N.B.: other implementations (Chez, Scheme->C and T, at least) use equal? as the equality test.

     Example:

          (remove 1 '(1 2 1 3 1 4 1 5))
             => (2 3 4 5)

          (remove 'foo '(bar baz bang))
             => (bar baz bang)

 -- Function: remove-if pred lst
     remove-if removes all ELEMENTs from LST where (PRED ELEMENT) is #t and returns everything that's left.

     Example:

          (remove-if number? '(1 2 3 4))
             => ()

          (remove-if even? '(1 2 3 4 5 6 7 8))
             => (1 3 5 7)

 -- Function: remove-if-not pred lst
     remove-if-not removes all ELEMENTs from LST for which (PRED ELEMENT) is #f and returns everything that's left.

     Example:

          (remove-if-not number? '(foo bar baz))
             => ()
          (remove-if-not odd? '(1 2 3 4 5 6 7 8))
             => (1 3 5 7)

 -- Function: has-duplicates? lst
     returns #t if 2 members of LST are equal?, #f otherwise.

     Example:

          (has-duplicates? '(1 2 3 4))
             => #f

          (has-duplicates? '(2 4 3 4))
             => #t

The procedure remove-duplicates uses member (rather than memv).

 -- Function: remove-duplicates lst
     returns a copy of LST with its duplicate members removed. Elements are considered duplicate if they are equal?.

     Example:

          (remove-duplicates '(1 2 3 4))
             => (1 2 3 4)

          (remove-duplicates '(2 4 3 4))
             => (2 4 3)

Lists as sequences
..................

 -- Function: position obj lst
     position returns the 0-based position of OBJ in LST, or #f if OBJ does not occur in LST.

     Example:

          (position 'foo '(foo bar baz bang))
             => 0
          (position 'baz '(foo bar baz bang))
             => 2
          (position 'oops '(foo bar baz bang))
             => #f

 -- Function: reduce p lst
     reduce combines all the elements of a sequence using a binary operation (the combination is left-associative).  For example, using +, one can add up all the elements.  reduce allows you to apply a function which accepts only two arguments to more than 2 objects.  Functional programmers usually refer to this as foldl. collect:reduce (see Collections) provides a version of collect generalized to collections.

     Example:

          (reduce + '(1 2 3 4))
             => 10
          (define (bad-sum . l) (reduce + l))
          (bad-sum 1 2 3 4)
             == (reduce + (1 2 3 4))
             == (+ (+ (+ 1 2) 3) 4)
          => 10
          (bad-sum)
             == (reduce + ())
             => ()
          (reduce string-append '("hello" "cruel" "world"))
             == (string-append (string-append "hello" "cruel") "world")
             => "hellocruelworld"
          (reduce anything '())
             => ()
          (reduce anything '(x))
             => x

     What follows is a rather non-standard implementation of reverse in terms of reduce and a combinator elsewhere called C.

          ;;; Contributed by Jussi Piitulainen (jpiitula @ ling.helsinki.fi)

          (define commute
            (lambda (f)
              (lambda (x y)
                (f y x))))

          (define reverse
            (lambda (args)
              (reduce-init (commute cons) '() args)))

 -- Function: reduce-init p init lst
     reduce-init is the same as reduce, except that it implicitly inserts INIT at the start of the list.  reduce-init is preferred if you want to handle the null list, the one-element, and lists with two or more elements consistently.  It is common to use the operator's idempotent as the initializer.  Functional programmers usually call this foldl.

     Example:

          (define (sum . l) (reduce-init + 0 l))
          (sum 1 2 3 4)
             == (reduce-init + 0 (1 2 3 4))
             == (+ (+ (+ (+ 0 1) 2) 3) 4)
             => 10
          (sum)
             == (reduce-init + 0 '())
             => 0

          (reduce-init string-append "@" '("hello" "cruel" "world"))
          ==
          (string-append (string-append (string-append "@" "hello")
                                         "cruel")
                         "world")
          => "@hellocruelworld"

     Given a differentiation of 2 arguments, diff, the following will differentiate by any number of variables.

          (define (diff* exp . vars)
            (reduce-init diff exp vars))

     Example:

          ;;; Real-world example:  Insertion sort using reduce-init.

          (define (insert l item)
            (if (null? l)
                (list item)
                (if (< (car l) item)
                    (cons (car l) (insert (cdr l) item))
                    (cons item l))))
          (define (insertion-sort l) (reduce-init insert '() l))

          (insertion-sort '(3 1 4 1 5)
             == (reduce-init insert () (3 1 4 1 5))
             == (insert (insert (insert (insert (insert () 3) 1) 4) 1) 5)
             == (insert (insert (insert (insert (3)) 1) 4) 1) 5)
             == (insert (insert (insert (1 3) 4) 1) 5)
             == (insert (insert (1 3 4) 1) 5)
             == (insert (1 1 3 4) 5)
             => (1 1 3 4 5)

 -- Function: last lst n
     last returns the last N elements of LST.  N must be a non-negative integer.

     Example:

          (last '(foo bar baz bang) 2)
             => (baz bang)
          (last '(1 2 3) 0)
             => 0

 -- Function: butlast lst n
     butlast returns all but the last N elements of LST.

     Example:

          (butlast '(a b c d) 3)
             => (a)
          (butlast '(a b c d) 4)
             => ()

last and butlast split a list into two parts when given identical arugments.

     (last '(a b c d e) 2)
        => (d e)
     (butlast '(a b c d e) 2)
        => (a b c)

 -- Function: nthcdr n lst
     nthcdr takes N cdrs of LST and returns the result.  Thus (nthcdr 3 LST) == (cdddr LST)

     Example:

          (nthcdr 2 '(a b c d))
             => (c d)
          (nthcdr 0 '(a b c d))
             => (a b c d)

 -- Function: butnthcdr n lst
     butnthcdr returns all but the nthcdr N elements of LST.

     Example:

          (butnthcdr 3 '(a b c d))
             => (a b c)
          (butnthcdr 4 '(a b c d))
             => (a b c d)

nthcdr and butnthcdr split a list into two parts when given identical arugments.

     (nthcdr 2 '(a b c d e))
        => (c d e)
     (butnthcdr 2 '(a b c d e))
        => (a b)

Destructive list operations
...........................

These procedures may mutate the list they operate on, but any such mutation is undefined.

 -- Procedure: nconc args
     nconc destructively concatenates its arguments.  (Compare this with append, which copies arguments rather than destroying them.) Sometimes called append! (see Rev2 Procedures).

     Example:  You want to find the subsets of a set.  Here's the obvious way:

          (define (subsets set)
            (if (null? set)
                '(())
                (append (mapcar (lambda (sub) (cons (car set) sub))
                                (subsets (cdr set)))
                        (subsets (cdr set)))))

     But that does way more consing than you need.  Instead, you could replace the append with nconc, since you don't have any need for all the intermediate results.

     Example:

          (define x '(a b c))
          (define y '(d e f))
          (nconc x y)
             => (a b c d e f)
          x
             => (a b c d e f)

     nconc is the same as append! in sc2.scm.

 -- Procedure: nreverse lst
     nreverse reverses the order of elements in LST by mutating cdrs of the list.  Sometimes called reverse!.

     Example:

          (define foo '(a b c))
          (nreverse foo)
             => (c b a)
          foo
             => (a)

     Some people have been confused about how to use nreverse, thinking that it doesn't return a value.  It needs to be pointed out that

          (set! lst (nreverse lst))

     is the proper usage, not

          (nreverse lst)

     The example should suffice to show why this is the case.

 -- Procedure: delete elt lst
 -- Procedure: delete-if pred lst
 -- Procedure: delete-if-not pred lst
     Destructive versions of remove remove-if, and remove-if-not.

     Example:

          (define lst (list 'foo 'bar 'baz 'bang))
          (delete 'foo lst)
             => (bar baz bang)
          lst
             => (foo bar baz bang)

          (define lst (list 1 2 3 4 5 6 7 8 9))
          (delete-if odd? lst)
             => (2 4 6 8)
          lst
             => (1 2 4 6 8)

     Some people have been confused about how to use delete, delete-if, and delete-if, thinking that they don't return a value.  It needs to be pointed out that

          (set! lst (delete el lst))

     is the proper usage, not

          (delete el lst)

     The examples should suffice to show why this is the case.

Non-List functions
..................

 -- Function: and? arg1 ...
     and? checks to see if all its arguments are true.  If they are, and? returns #t, otherwise, #f.  (In contrast to and, this is a function, so all arguments are always evaluated and in an unspecified order.)

     Example:

          (and? 1 2 3)
             => #t
          (and #f 1 2)
             => #f

 -- Function: or? arg1 ...
     or? checks to see if any of its arguments are true.  If any is true, or? returns #t, and #f otherwise.  (To or as and? is to and.)

     Example:

          (or? 1 2 #f)
             => #t
          (or? #f #f #f)
             => #f

 -- Function: atom? object
     Returns #t if OBJECT is not a pair and #f if it is pair.  (Called atom in Common LISP.)

          (atom? 1)
             => #t
          (atom? '(1 2))
             => #f
          (atom? #(1 2))   ; dubious!
             => #t

Tree operations
---------------

(require 'tree)

These are operations that treat lists a representations of trees.

 -- Function: subst new old tree
 -- Function: subst new old tree equ?
 -- Function: substq new old tree
 -- Function: substv new old tree
     subst makes a copy of TREE, substituting NEW for every subtree or leaf of TREE which is equal? to OLD and returns a modified tree.  The original TREE is unchanged, but may share parts with the result.

     substq and substv are similar, but test against OLD using eq? and eqv? respectively.  If subst is called with a fourth argument, EQU? is the equality predicate.

     Examples:

          (substq 'tempest 'hurricane '(shakespeare wrote (the hurricane)))
             => (shakespeare wrote (the tempest))
          (substq 'foo '() '(shakespeare wrote (twelfth night)))
             => (shakespeare wrote (twelfth night . foo) . foo)
          (subst '(a . cons) '(old . pair)
                 '((old . spice) ((old . shoes) old . pair) (old . pair)))
             => ((old . spice) ((old . shoes) a . cons) (a . cons))

 -- Function: copy-tree tree
     Makes a copy of the nested list structure TREE using new pairs and returns it.  All levels are copied, so that none of the pairs in the tree are eq? to the original ones -- only the leaves are.

     Example:

          (define bar '(bar))
          (copy-tree (list bar 'foo))
             => ((bar) foo)
          (eq? bar (car (copy-tree (list bar 'foo))))
             => #f

Chapter Ordering
----------------

(require 'chapter-order)

The chap: functions deal with strings which are ordered like chapter numbers (or letters) in a book.  Each section of the string consists of consecutive numeric or consecutive aphabetic characters of like case.

 -- Function: chap:string<? string1 string2
     Returns #t if the first non-matching run of alphabetic upper-case or the first non-matching run of alphabetic lower-case or the first non-matching run of numeric characters of STRING1 is string<? than the corresponding non-matching run of characters of STRING2.

          (chap:string<? "a.9" "a.10")                    => #t
          (chap:string<? "4c" "4aa")                      => #t
          (chap:string<? "Revised^{3.99}" "Revised^{4}")  => #t

 -- Function: chap:string>? string1 string2
 -- Function: chap:string<=? string1 string2
 -- Function: chap:string>=? string1 string2
     Implement the corresponding chapter-order predicates.

 -- Function: chap:next-string string
     Returns the next string in the chapter order.  If STRING has no alphabetic or numeric characters, (string-append STRING "0") is returnd.  The argument to chap:next-string will always be chap:string<? than the result.

          (chap:next-string "a.9")                => "a.10"
          (chap:next-string "4c")                 => "4d"
          (chap:next-string "4z")                 => "4aa"
          (chap:next-string "Revised^{4}")        => "Revised^{5}"

Sorting
-------

(require 'sort)

Many Scheme systems provide some kind of sorting functions.  They do not, however, always provide the same sorting functions, and those that I have had the opportunity to test provided inefficient ones (a common blunder is to use quicksort which does not perform well).

Because sort and sort! are not in the standard, there is very little agreement about what these functions look like.  For example, Dybvig says that Chez Scheme provides

     (merge predicate list1 list2)
     (merge! predicate list1 list2)
     (sort predicate list)
     (sort! predicate list)

while MIT Scheme 7.1, following Common LISP, offers unstable

     (sort list predicate)

TI PC Scheme offers

     (sort! list/vector predicate?)

and Elk offers

     (sort list/vector predicate?)
     (sort! list/vector predicate?)

Here is a comprehensive catalogue of the variations I have found.

 1. Both sort and sort! may be provided.

 2. sort may be provided without sort!.

 3. sort! may be provided without sort.

 4. Neither may be provided.

 5. The sequence argument may be either a list or a vector.

 6. The sequence argument may only be a list.

 7. The sequence argument may only be a vector.

 8. The comparison function may be expected to behave like <.

 9. The comparison function may be expected to behave like <=.

 10. The interface may be (sort predicate? sequence).

 11. The interface may be (sort sequence predicate?).

 12. The interface may be (sort sequence &optional (predicate? <)).

 13. The sort may be stable.

 14. The sort may be unstable.

All of this variation really does not help anybody.  A nice simple merge sort is both stable and fast (quite a lot faster than quick sort).

I am providing this source code with no restrictions at all on its use (but please retain D.H.D.Warren's credit for the original idea).  You may have to rename some of these functions in order to use them in a system which already provides incompatible or inferior sorts.  For each of the functions, only the top-level define needs to be edited to do that.

I could have given these functions names which would not clash with any Scheme that I know of, but I would like to encourage implementors to converge on a single interface, and this may serve as a hint.  The argument order for all functions has been chosen to be as close to Common LISP as made sense, in order to avoid NIH-itis.

Each of the five functions has a required last parameter which is a comparison function.  A comparison function f is a function of 2 arguments which acts like <.  For example,

     (not (f x x))
     (and (f x y) (f y z)) == (f x z)

The standard functions <, >, char<?, char>?, char-ci<?, char-ci>?, string<?, string>?, string-ci<?, and string-ci>? are suitable for use as comparison functions.  Think of (less? x y) as saying when x must not precede y.

 -- Function: sorted? sequence less?
     Returns #t when the sequence argument is in non-decreasing order according to LESS? (that is, there is no adjacent pair ... x y ... for which (less? y x)).

     Returns #f when the sequence contains at least one out-of-order pair.  It is an error if the sequence is neither a list nor a vector.

 -- Function: merge list1 list2 less?
     This merges two lists, producing a completely new list as result.  I gave serious consideration to producing a Common-LISP-compatible version.  However, Common LISP's sort is our sort! (well, in fact Common LISP's stable-sort is our sort!, merge sort is fast as well as stable!) so adapting CL code to Scheme takes a bit of work anyway.  I did, however, appeal to CL to determine the order of the arguments.

 -- Procedure: merge! list1 list2 less?
     Merges two lists, re-using the pairs of LIST1 and LIST2 to build the result.  If the code is compiled, and LESS? constructs no new pairs, no pairs at all will be allocated.  The first pair of the result will be either the first pair of LIST1 or the first pair of LIST2, but you can't predict which.

     The code of merge and merge! could have been quite a bit simpler, but they have been coded to reduce the amount of work done per iteration.  (For example, we only have one null? test per iteration.)

 -- Function: sort sequence less?
     Accepts either a list or a vector, and returns a new sequence which is sorted.  The new sequence is the same type as the input.  Always (sorted? (sort sequence less?) less?).  The original sequence is not altered in any way.  The new sequence shares its elements with the old one; no elements are copied.

 -- Procedure: sort! sequence less?
     Returns its sorted result in the original boxes.  If the original sequence is a list, no new storage is allocated at all.  If the original sequence is a vector, the sorted elements are put back in the same vector.

     Some people have been confused about how to use sort!, thinking that it doesn't return a value.  It needs to be pointed out that

          (set! slist (sort! slist <))

     is the proper usage, not

          (sort! slist <)

Note that these functions do not accept a CL-style :key argument.  A simple device for obtaining the same expressiveness is to define

     (define (keyed less? key)
       (lambda (x y) (less? (key x) (key y))))

and then, when you would have written

     (sort a-sequence #'my-less :key #'my-key)

in Common LISP, just write

     (sort! a-sequence (keyed my-less? my-key))

in Scheme.

Topological Sort
----------------

(require 'topological-sort) or (require 'tsort)

The algorithm is inspired by Cormen, Leiserson and Rivest (1990) Introduction to Algorithms, chapter 23.

 -- Function: tsort dag pred
 -- Function: topological-sort dag pred
     where

     dag
          is a list of sublists.  The car of each sublist is a vertex.  The cdr is the adjacency list of that vertex, i.e. a list of all vertices to which there exists an edge from the car vertex.

     pred
          is one of eq?, eqv?, equal?, =, char=?, char-ci=?, string=?, or string-ci=?.

     Sort the directed acyclic graph DAG so that for every edge from vertex U to V, U will come before V in the resulting list of vertices.

     Time complexity: O (|V| + |E|)

     Example (from Cormen):

          Prof. Bumstead topologically sorts his clothing when getting dressed.  The first argument to `tsort' describes which garments he needs to put on before others.  (For example, Prof Bumstead needs to put on his shirt before he puts on his tie or his belt.)  `tsort' gives the correct order of dressing:

          (require 'tsort)
          (tsort '((shirt tie belt)
                   (tie jacket)
                   (belt jacket)
                   (watch)
                   (pants shoes belt)
                   (undershorts pants shoes)
                   (socks shoes))
                 eq?)
          =>
          (socks undershorts pants shoes watch shirt belt tie jacket)

Hashing
-------

(require 'hash)

These hashing functions are for use in quickly classifying objects. Hash tables use these functions.

 -- Function: hashq obj k
 -- Function: hashv obj k
 -- Function: hash obj k
     Returns an exact non-negative integer less than K.  For each non-negative integer less than K there are arguments OBJ for which the hashing functions applied to OBJ and K returns that integer.

     For hashq, (eq? obj1 obj2) implies (= (hashq obj1 k) (hashq obj2)).

     For hashv, (eqv? obj1 obj2) implies (= (hashv obj1 k) (hashv obj2)).

     For hash, (equal? obj1 obj2) implies (= (hash obj1 k) (hash obj2)).

     hash, hashv, and hashq return in time bounded by a constant.  Notice that items having the same hash implies the items have the same hashv implies the items have the same hashq.

Space-Filling Curves
--------------------

(require 'sierpinski)

 -- Function: make-sierpinski-indexer max-coordinate
     Returns a procedure (eg hash-function) of 2 numeric arguments which preserves nearness in its mapping from NxN to N.

     MAX-COORDINATE is the maximum coordinate (a positive integer) of a population of points.  The returned procedures is a function that takes the x and y coordinates of a point, (non-negative integers) and returns an integer corresponding to the relative position of that point along a Sierpinski curve.  (You can think of this as computing a (pseudo-) inverse of the Sierpinski spacefilling curve.)

     Example use: Make an indexer (hash-function) for integer points lying in square of integer grid points [0,99]x[0,99]:

          (define space-key (make-sierpinski-indexer 100))

     Now let's compute the index of some points:

          (space-key 24 78)               => 9206
          (space-key 23 80)               => 9172

     Note that locations (24, 78) and (23, 80) are near in index and therefore, because the Sierpinski spacefilling curve is continuous, we know they must also be near in the plane.  Nearness in the plane does not, however, necessarily correspond to nearness in index, although it tends to be so.

     Example applications:

       * Sort points by Sierpinski index to get heuristic solution to travelling salesman problem.  For details of performance, see L. Platzman and J. Bartholdi, "Spacefilling curves and the Euclidean travelling salesman problem", JACM 36(4):719--737 (October 1989) and references therein.

       * Use Sierpinski index as key by which to store 2-dimensional data in a 1-dimensional data structure (such as a table).  Then locations that are near each other in 2-d space will tend to be near each other in 1-d data structure; and locations that are near in 1-d data structure will be near in 2-d space.  This can significantly speed retrieval from secondary storage because contiguous regions in the plane will tend to correspond to contiguous regions in secondary storage.  (This is a standard technique for managing CAD/CAM or geographic data.)

Soundex
-------

(require 'soundex)

 -- Function: soundex name
     Computes the soundex hash of NAME.  Returns a string of an initial letter and up to three digits between 0 and 6.  Soundex supposedly has the property that names that sound similar in normal English pronunciation tend to map to the same key.

     Soundex was a classic algorithm used for manual filing of personal records before the advent of computers.  It performs adequately for English names but has trouble with other languages.

     See Knuth, Vol. 3 Sorting and searching, pp 391--2

     To manage unusual inputs, soundex omits all non-alphabetic characters.  Consequently, in this implementation:

          (soundex <string of blanks>)    => ""
          (soundex "")                    => ""

     Examples from Knuth:

          (map soundex '("Euler" "Gauss" "Hilbert" "Knuth"
                                 "Lloyd" "Lukasiewicz"))
                  => ("E460" "G200" "H416" "K530" "L300" "L222")

          (map soundex '("Ellery" "Ghosh" "Heilbronn" "Kant"
                                  "Ladd" "Lissajous"))
                  => ("E460" "G200" "H416" "K530" "L300" "L222")

     Some cases in which the algorithm fails (Knuth):

          (map soundex '("Rogers" "Rodgers"))     => ("R262" "R326")

          (map soundex '("Sinclair" "St. Clair")) => ("S524" "S324")

          (map soundex '("Tchebysheff" "Chebyshev")) => ("T212" "C121")

String Search
-------------

(require 'string-search)

 -- Procedure: string-index string char
 -- Procedure: string-index-ci string char
     Returns the index of the first occurence of CHAR within STRING, or #f if the STRING does not contain a character CHAR.

 -- Procedure: string-reverse-index string char
 -- Procedure: string-reverse-index-ci string char
     Returns the index of the last occurence of CHAR within STRING, or #f if the STRING does not contain a character CHAR.

 -- procedure: substring? pattern string
 -- procedure: substring-ci? pattern string
     Searches STRING to see if some substring of STRING is equal to PATTERN.  substring? returns the index of the first character of the first substring of STRING that is equal to PATTERN; or #f if STRING does not contain PATTERN.

          (substring? "rat" "pirate") =>  2
          (substring? "rat" "outrage") =>  #f
          (substring? "" any-string) =>  0

 -- Procedure: find-string-from-port? str in-port max-no-chars
     Looks for a string STR within the first MAX-NO-CHARS chars of the input port IN-PORT.

 -- Procedure: find-string-from-port? str in-port
     When called with two arguments, the search span is limited by the end of the input stream.

 -- Procedure: find-string-from-port? str in-port char
     Searches up to the first occurrence of character CHAR in STR.

 -- Procedure: find-string-from-port? str in-port proc
     Searches up to the first occurrence of the procedure PROC returning non-false when called with a character (from IN-PORT) argument.

     When the STR is found, find-string-from-port? returns the number of characters it has read from the port, and the port is set to read the first char after that (that is, after the STR) The function returns #f when the STR isn't found.

     find-string-from-port? reads the port strictly sequentially, and does not perform any buffering.  So find-string-from-port? can be used even if the IN-PORT is open to a pipe or other communication channel.

 -- Function: string-subst txt old1 new1 ...
     Returns a copy of string TXT with all occurrences of string OLD1 in TXT replaced with NEW1, OLD2 replaced with NEW2 ....

Sequence Comparison
-------------------

(require 'diff)

     [file differ.txi not included]

Procedures
==========

Anything that doesn't fall neatly into any of the other categories winds up here.

Type Coercion
-------------

(require 'coerce)

     [file coerce.txi not included]

String-Case
-----------

(require 'string-case)

 -- Procedure: string-upcase str
 -- Procedure: string-downcase str
 -- Procedure: string-capitalize str
     The obvious string conversion routines.  These are non-destructive.

 -- Function: string-upcase! str
 -- Function: string-downcase! str
 -- Function: string-captialize! str
     The destructive versions of the functions above.

 -- Function: string-ci->symbol str
     Converts string STR to a symbol having the same case as if the symbol had been read.

 -- Function: symbol-append obj1 ...
     Converts OBJ1 ... to strings, appends them, and converts to a symbol which is returned.  Strings and numbers are converted to read's symbol case; the case of symbol characters is not changed.  #f is converted to the empty string (symbol).

 -- Function: StudlyCapsExpand str delimiter
 -- Function: StudlyCapsExpand str
     DELIMITER must be a string or character.  If absent, DELIMITER defaults to -.  StudlyCapsExpand returns a copy of STR where DELIMITER is inserted between each lower-case character immediately followed by an upper-case character; and between two upper-case characters immediately followed by a lower-case character.

          (StudlyCapsExpand "aX" " ")   => "a X"
          (StudlyCapsExpand "aX" "..")  => "a..X"
          (StudlyCapsExpand "AX")       => "AX"
          (StudlyCapsExpand "Ax")       => "Ax"
          (StudlyCapsExpand "AXLE")     => "AXLE"
          (StudlyCapsExpand "aAXACz")   => "a-AXA-Cz"
          (StudlyCapsExpand "AaXACz")   => "Aa-XA-Cz"
          (StudlyCapsExpand "AAaXACz")  => "A-Aa-XA-Cz"
          (StudlyCapsExpand "AAaXAC")   => "A-Aa-XAC"

String Ports
------------

(require 'string-port)

 -- Procedure: call-with-output-string proc
     PROC must be a procedure of one argument.  This procedure calls PROC with one argument: a (newly created) output port.  When the function returns, the string composed of the characters written into the port is returned.

 -- Procedure: call-with-input-string string proc
     PROC must be a procedure of one argument.  This procedure calls PROC with one argument: an (newly created) input port from which STRING's contents may be read.  When PROC returns, the port is closed and the value yielded by the procedure PROC is returned.

Line I/O
--------

(require 'line-i/o)

     [file lineio.txi not included]

Multi-Processing
----------------

(require 'process)

This module implements asynchronous (non-polled) time-sliced multi-processing in the SCM Scheme implementation using procedures alarm and alarm-interrupt. Until this is ported to another implementation, consider it an example of writing schedulers in Scheme.

 -- Procedure: add-process! proc
     Adds proc, which must be a procedure (or continuation) capable of accepting accepting one argument, to the process:queue.  The value returned is unspecified.  The argument to PROC should be ignored.  If PROC returns, the process is killed.

 -- Procedure: process:schedule!
     Saves the current process on process:queue and runs the next process from process:queue.  The value returned is unspecified.

 -- Procedure: kill-process!
     Kills the current process and runs the next process from process:queue.  If there are no more processes on process:queue, (slib:exit) is called (see System).

Metric Units
------------

(require 'metric-units)

http://swissnet.ai.mit.edu/~jaffer/MIXF.html

Metric Interchange Format is a character string encoding for numerical values and units which:

  * is unambiguous in all locales;

  * uses only [TOG] "Portable Character Set" characters matching "Basic Latin" characters in Plane 0 of the Universal Character Set [UCS];

  * is transparent to [UTF-7] and [UTF-8] UCS transformation formats;

  * is human readable and writable;

  * is machine readable and writable;

  * incorporates SI prefixes and units;

  * incorporates [ISO 6093] numbers; and

  * incorporates [IEC 60027-2] binary prefixes.

In the expression for the value of a quantity, the unit symbol is placed after the numerical value.  A dot (PERIOD, .) is placed between the numerical value and the unit symbol.

Within a compound unit, each of the base and derived symbols can optionally have an attached SI prefix.

Unit symbols formed from other unit symbols by multiplication are indicated by means of a dot (PERIOD, .) placed between them.

Unit symbols formed from other unit symbols by division are indicated by means of a SOLIDUS (/) or negative exponents.  The SOLIDUS must not be repeated in the same compound unit unless contained within a parenthesized subexpression.

The grouping formed by a prefix symbol attached to a unit symbol constitutes a new inseparable symbol (forming a multiple or submultiple of the unit concerned) which can be raised to a positive or negative power and which can be combined with other unit symbols to form compound unit symbols.

The grouping formed by surrounding compound unit symbols with parentheses (( and )) constitutes a new inseparable symbol which can be raised to a positive or negative power and which can be combined with other unit symbols to form compound unit symbols.

Compound prefix symbols, that is, prefix symbols formed by the juxtaposition of two or more prefix symbols, are not permitted.

Prefix symbols are not used with the time-related unit symbols min (minute), h (hour), d (day).  No prefix symbol may be used with dB (decibel).  Only submultiple prefix symbols may be used with the unit symbols L (liter), Np (neper), o (degree), oC (degree Celsius), rad (radian), and sr (steradian).  Submultiple prefix symbols may not be used with the unit symbols t (metric ton), r (revolution), or Bd (baud).

A unit exponent follows the unit, separated by a CIRCUMFLEX (^). Exponents may be positive or negative.  Fractional exponents must be parenthesized.

SI Prefixes
...........

            Factor     Name    Symbol  |  Factor     Name    Symbol
            ======     ====    ======  |  ======     ====    ======
             1e24      yotta      Y    |   1e-1      deci       d
             1e21      zetta      Z    |   1e-2      centi      c
             1e18      exa        E    |   1e-3      milli      m
             1e15      peta       P    |   1e-6      micro      u
             1e12      tera       T    |   1e-9      nano       n
             1e9       giga       G    |   1e-12     pico       p
             1e6       mega       M    |   1e-15     femto      f
             1e3       kilo       k    |   1e-18     atto       a
             1e2       hecto      h    |   1e-21     zepto      z
             1e1       deka       da   |   1e-24     yocto      y

Binary Prefixes
...............

These binary prefixes are valid only with the units B (byte) and bit. However, decimal prefixes can also be used with bit; and decimal multiple (not submultiple) prefixes can also be used with B (byte).

                     Factor       (power-of-2)  Name  Symbol
                     ======       ============  ====  ======
            1.152921504606846976e18  (2^60)     exbi    Ei
               1.125899906842624e15  (2^50)     pebi    Pi
                  1.099511627776e12  (2^40)     tebi    Ti
                     1.073741824e9   (2^30)     gibi    Gi
                        1.048576e6   (2^20)     mebi    Mi
                           1.024e3   (2^10)     kibi    Ki

Unit Symbols
............

         Type of Quantity      Name          Symbol   Equivalent
         ================      ====          ======   ==========
     time                      second           s
     time                      minute           min = 60.s
     time                      hour             h   = 60.min
     time                      day              d   = 24.h
     frequency                 hertz            Hz    s^-1
     signaling rate            baud             Bd    s^-1
     length                    meter            m
     volume                    liter            L     dm^3
     plane angle               radian           rad
     solid angle               steradian        sr    rad^2
     plane angle               revolution     * r   = 6.283185307179586.rad
     plane angle               degree         * o   = 2.777777777777778e-3.r
     information capacity      bit              bit
     information capacity      byte, octet      B   = 8.bit
     mass                      gram             g
     mass                      ton              t     Mg
     mass              unified atomic mass unit u   = 1.66053873e-27.kg
     amount of substance       mole             mol
     catalytic activity        katal            kat   mol/s
     thermodynamic temperature kelvin           K
     centigrade temperature    degree Celsius   oC
     luminous intensity        candela          cd
     luminous flux             lumen            lm    cd.sr
     illuminance               lux              lx    lm/m^2
     force                     newton           N     m.kg.s^-2
     pressure, stress          pascal           Pa    N/m^2
     energy, work, heat        joule            J     N.m
     energy                    electronvolt     eV  = 1.602176462e-19.J
     power, radiant flux       watt             W     J/s
     logarithm of power ratio  neper            Np
     logarithm of power ratio  decibel        * dB  = 0.1151293.Np
     electric current          ampere           A
     electric charge           coulomb          C     s.A
     electric potential, EMF   volt             V     W/A
     capacitance               farad            F     C/V
     electric resistance       ohm              Ohm   V/A
     electric conductance      siemens          S     A/V
     magnetic flux             weber            Wb    V.s
     magnetic flux density     tesla            T     Wb/m^2
     inductance                henry            H     Wb/A
     radionuclide activity     becquerel        Bq    s^-1
     absorbed dose energy      gray             Gy    m^2.s^-2
     dose equivalent           sievert          Sv    m^2.s^-2

* The formulas are:

  * r/rad = 8 * atan(1)

  * o/r = 1 / 360

  * db/Np = ln(10) / 20

 -- Function: si:conversion-factor to-unit from-unit
     If the strings FROM-UNIT and TO-UNIT express valid unit expressions for quantities of the same unit-dimensions, then the value returned by si:conversion-factor will be such that multiplying a numerical value expressed in FROM-UNITs by the returned conversion factor yields the numerical value expressed in TO-UNITs.

     Otherwise, si:conversion-factor returns:

     -3
          if neither FROM-UNIT nor TO-UNIT is a syntactically valid unit.

     -2
          if FROM-UNIT is not a syntactically valid unit.

     -1
          if TO-UNIT is not a syntactically valid unit.

     0
          if linear conversion (by a factor) is not possible.

     (si:conversion-factor "km/s" "m/s" ) => 0.001
     (si:conversion-factor "N"    "m/s" ) => 0
     (si:conversion-factor "moC"  "oC"  ) => 1000
     (si:conversion-factor "mK"   "oC"  ) => 0
     (si:conversion-factor "rad"  "o"   ) => 0.0174533
     (si:conversion-factor "K"    "o"   ) => 0
     (si:conversion-factor "K"    "K"   ) => 1
     (si:conversion-factor "oK"   "oK"  ) => -3
     (si:conversion-factor ""     "s/s" ) => 1
     (si:conversion-factor "km/h" "mph" ) => -2

Standards Support
=================

RnRS
----

The r2rs, r3rs, r4rs, and r5rs features attempt to provide procedures and macros to bring a Scheme implementation to the desired version of Scheme.

 -- Feature: r2rs
     Requires features implementing procedures and optional procedures specified by Revised^2 Report on the Algorithmic Language Scheme; namely rev3-procedures and rev2-procedures.

 -- Feature: r3rs
     Requires features implementing procedures and optional procedures specified by Revised^3 Report on the Algorithmic Language Scheme; namely rev3-procedures.

     Note: SLIB already mandates the r3rs procedures which can be portably implemented in r4rs implementations.

 -- Feature: r4rs
     Requires features implementing procedures and optional procedures specified by Revised^4 Report on the Algorithmic Language Scheme; namely rev4-optional-procedures.

 -- Feature: r5rs
     Requires features implementing procedures and optional procedures specified by Revised^5 Report on the Algorithmic Language Scheme; namely values, macro, and eval.

With-File
---------

(require 'with-file)

 -- Function: with-input-from-file file thunk
 -- Function: with-output-to-file file thunk
     Description found in R4RS.

Transcripts
-----------

(require 'transcript)

 -- Function: transcript-on filename
 -- Function: transcript-off filename
     Redefines read-char, read, write-char, write, display, and newline.

Rev2 Procedures
---------------

(require 'rev2-procedures)

The procedures below were specified in the Revised^2 Report on Scheme.  N.B.: The symbols 1+ and -1+ are not R4RS syntax.  Scheme->C, for instance, chokes on this module.

 -- Procedure: substring-move-left! string1 start1 end1 string2 start2
 -- Procedure: substring-move-right! string1 start1 end1 string2 start2
     STRING1 and STRING2 must be a strings, and START1, START2 and END1 must be exact integers satisfying

          0 <= START1 <= END1 <= (string-length STRING1)
          0 <= START2 <= END1 - START1 + START2 <= (string-length STRING2)

     substring-move-left! and substring-move-right! store characters of STRING1 beginning with index START1 (inclusive) and ending with index END1 (exclusive) into STRING2 beginning with index START2 (inclusive).

     substring-move-left! stores characters in time order of increasing indices.  substring-move-right! stores characters in time order of increasing indeces.

 -- Procedure: substring-fill! string start end char
     Fills the elements START--END of STRING with the character CHAR.

 -- Function: string-null? str
     == (= 0 (string-length STR))

 -- Procedure: append! pair1 ...
     Destructively appends its arguments.  Equivalent to nconc.

 -- Function: 1+ n
     Adds 1 to N.

 -- Function: -1+ n
     Subtracts 1 from N.

 -- Function: <?
 -- Function: <=?
 -- Function: >?
 -- Function: >=?
     These are equivalent to the procedures of the same name but without the trailing ?.

Rev4 Optional Procedures
------------------------

(require 'rev4-optional-procedures)

For the specification of these optional procedures, see Standard procedures (Revised(4) Scheme).

 -- Function: list-tail l p

 -- Function: string->list s

 -- Function: list->string l

 -- Function: string-copy

 -- Procedure: string-fill! s obj

 -- Function: list->vector l

 -- Function: vector->list s

 -- Procedure: vector-fill! s obj

Multi-argument / and -
----------------------

(require 'multiarg/and-)

For the specification of these optional forms, see Numerical operations (Revised(4) Scheme).  The two-arg:* forms are only defined if the implementation does not support the many-argument forms.

 -- Function: two-arg:/ n1 n2
     The original two-argument version of /.

 -- Function: / dividend divisor1 ...

 -- Function: two-arg:- n1 n2
     The original two-argument version of -.

 -- Function: - minuend subtrahend1 ...

Multi-argument Apply
--------------------

(require 'multiarg-apply)

For the specification of this optional form, see Control features (Revised(4) Scheme).

 -- Function: two-arg:apply proc l
     The implementation's native apply.  Only defined for implementations which don't support the many-argument version.

 -- Function: apply proc arg1 ...

Rationalize
-----------

(require 'rationalize)

The procedure rationalize is interesting because most programming languages do not provide anything analogous to it.  Thanks to Alan Bawden for contributing this algorithm.

 -- Function: rationalize x y
     Computes the correct result for exact arguments (provided the implementation supports exact rational numbers of unlimited precision); and produces a reasonable answer for inexact arguments when inexact arithmetic is implemented using floating-point.

Rationalize has limited use in implementations lacking exact (non-integer) rational numbers.  The following procedures return a list of the numerator and denominator.

 -- Function: find-ratio x y
     find-ratio returns the list of the simplest numerator and denominator whose quotient differs from X by no more than Y.

          (find-ratio 3/97 .0001)             => (3 97)
          (find-ratio 3/97 .001)              => (1 32)

 -- Function: find-ratio-between x y
     find-ratio-between returns the list of the simplest numerator and denominator between X and Y.

          (find-ratio-between 2/7 3/5)        => (1 2)
          (find-ratio-between -3/5 -2/7)      => (-1 2)

Promises
--------

(require 'promise)

 -- Function: make-promise proc

Change occurrences of (delay EXPRESSION) to (make-promise (lambda () EXPRESSION)) and (define force promise:force) to implement promises if your implementation doesn't support them (see Control features (Revised(4) Scheme)).

Dynamic-Wind
------------

(require 'dynamic-wind)

This facility is a generalization of Common LISP unwind-protect, designed to take into account the fact that continuations produced by call-with-current-continuation may be reentered.

 -- Procedure: dynamic-wind thunk1 thunk2 thunk3
     The arguments THUNK1, THUNK2, and THUNK3 must all be procedures of no arguments (thunks).

     dynamic-wind calls THUNK1, THUNK2, and then THUNK3.  The value returned by THUNK2 is returned as the result of dynamic-wind.  THUNK3 is also called just before control leaves the dynamic context of THUNK2 by calling a continuation created outside that context.  Furthermore, THUNK1 is called before reentering the dynamic context of THUNK2 by calling a continuation created inside that context.  (Control is inside the context of THUNK2 if THUNK2 is on the current return stack).

     Warning: There is no provision for dealing with errors or interrupts.  If an error or interrupt occurs while using dynamic-wind, the dynamic environment will be that in effect at the time of the error or interrupt.

Eval
----

(require 'eval)

 -- Function: eval expression environment-specifier

     Evaluates EXPRESSION in the specified environment and returns its value.  EXPRESSION must be a valid Scheme expression represented as data, and ENVIRONMENT-SPECIFIER must be a value returned by one of the three procedures described below.  Implementations may extend eval to allow non-expression programs (definitions) as the first argument and to allow other values as environments, with the restriction that eval is not allowed to create new bindings in the environments associated with null-environment or scheme-report-environment.

          (eval '(* 7 3) (scheme-report-environment 5))
                                                             =>  21

          (let ((f (eval '(lambda (f x) (f x x))
                         (null-environment))))
            (f + 10))
                                                             =>  20

 -- Function: scheme-report-environment version
 -- Function: null-environment version
 -- Function: null-environment

     VERSION must be an exact non-negative integer N corresponding to a version of one of the Revised^N Reports on Scheme.  Scheme-report-environment returns a specifier for an environment that contains the set of bindings specified in the corresponding report that the implementation supports. Null-environment returns a specifier for an environment that contains only the (syntactic) bindings for all the syntactic keywords defined in the given version of the report.

     Not all versions may be available in all implementations at all times. However, an implementation that conforms to version N of the Revised^N Reports on Scheme must accept version N.  An error is signalled if the specified version is not available.

     The effect of assigning (through the use of eval) a variable bound in a scheme-report-environment (for example car) is unspecified. Thus the environments specified by scheme-report-environment may be immutable.

 -- Function: interaction-environment

     This optional procedure returns a specifier for the environment that contains implementation-defined bindings, typically a superset of those listed in the report.  The intent is that this procedure will return the environment in which the implementation would evaluate expressions dynamically typed by the user.

Here are some more eval examples:

     (require 'eval)
     => #<unspecified>
     (define car 'volvo)
     => #<unspecified>
     car
     => volvo
     (eval 'car (interaction-environment))
     => volvo
     (eval 'car (scheme-report-environment 5))
     => #<primitive-procedure car>
     (eval '(eval 'car (interaction-environment))
           (scheme-report-environment 5))
     => volvo
     (eval '(eval '(set! car 'buick) (interaction-environment))
           (scheme-report-environment 5))
     => #<unspecified>
     car
     => buick
     (eval 'car (scheme-report-environment 5))
     => #<primitive-procedure car>
     (eval '(eval 'car (interaction-environment))
           (scheme-report-environment 5))
     => buick

Values
------

(require 'values)

 -- Function: values obj ...
     values takes any number of arguments, and passes (returns) them to its continuation.

 -- Function: call-with-values thunk proc
     THUNK must be a procedure of no arguments, and PROC must be a procedure.  call-with-values calls THUNK with a continuation that, when passed some values, calls PROC with those values as arguments.

     Except for continuations created by the call-with-values procedure, all continuations take exactly one value, as now; the effect of passing no value or more than one value to continuations that were not created by the call-with-values procedure is unspecified.

SRFI
----

     [file srfi.txi not included]

SRFI-1
......

     [file srfi-1.txi not included]

Session Support
===============

Repl
----

(require 'repl)

Here is a read-eval-print-loop which, given an eval, evaluates forms.

 -- Procedure: repl:top-level repl:eval
     reads, repl:evals and writes expressions from (current-input-port) to (current-output-port) until an end-of-file is encountered.  load, slib:eval, slib:error, and repl:quit dynamically bound during repl:top-level.

 -- Procedure: repl:quit
     Exits from the invocation of repl:top-level.

The repl: procedures establish, as much as is possible to do portably, a top level environment supporting macros. repl:top-level uses dynamic-wind to catch error conditions and interrupts.  If your implementation supports this you are all set.

Otherwise, if there is some way your implementation can catch error conditions and interrupts, then have them call slib:error.  It will display its arguments and reenter repl:top-level. slib:error dynamically bound by repl:top-level.

To have your top level loop always use macros, add any interrupt catching lines and the following lines to your Scheme init file:

     (require 'macro)
     (require 'repl)
     (repl:top-level macro:eval)

Quick Print
-----------

(require 'qp)

When displaying error messages and warnings, it is paramount that the output generated for circular lists and large data structures be limited.  This section supplies a procedure to do this.  It could be much improved.

     Notice that the neccessity for truncating output eliminates Common-Lisp's Format from consideration; even when variables *print-level* and *print-level* are set, huge strings and bit-vectors are not limited.

 -- Procedure: qp arg1 ...
 -- Procedure: qpn arg1 ...
 -- Procedure: qpr arg1 ...
     qp writes its arguments, separated by spaces, to (current-output-port).  qp compresses printing by substituting ... for substructure it does not have sufficient room to print.  qpn is like qp but outputs a newline before returning.  qpr is like qpn except that it returns its last argument.

 -- Variable: *qp-width*
     *qp-width* is the largest number of characters that qp should use.

Debug
-----

(require 'debug)

Requiring debug automatically requires trace and break.

An application with its own datatypes may want to substitute its own printer for qp.  This example shows how to do this:

     (define qpn (lambda args) ...)
     (provide 'qp)
     (require 'debug)

 -- Procedure: trace-all file ...
     Traces (see Trace) all procedures defined at top-level in file ....
 -- Procedure: track-all file ...
     Tracks (see Trace) all procedures defined at top-level in file ....
 -- Procedure: stack-all file ...
     Stacks (see Trace) all procedures defined at top-level in file ....

 -- Procedure: break-all file ...
     Breakpoints (see Breakpoints) all procedures defined at top-level in file ....

Breakpoints
-----------

(require 'break)

 -- Function: init-debug
     If your Scheme implementation does not support break or abort, a message will appear when you (require 'break) or (require 'debug) telling you to type (init-debug).  This is in order to establish a top-level continuation.  Typing (init-debug) at top level sets up a continuation for break.

 -- Function: breakpoint arg1 ...
     Returns from the top level continuation and pushes the continuation from which it was called on a continuation stack.

 -- Function: continue
     Pops the topmost continuation off of the continuation stack and returns an unspecified value to it.

 -- Function: continue arg1 ...
     Pops the topmost continuation off of the continuation stack and returns ARG1 ... to it.

 -- Macro: break proc1 ...
     Redefines the top-level named procedures given as arguments so that breakpoint is called before calling PROC1 ....
 -- Macro: break
     With no arguments, makes sure that all the currently broken identifiers are broken (even if those identifiers have been redefined) and returns a list of the broken identifiers.

 -- Macro: unbreak proc1 ...
     Turns breakpoints off for its arguments.
 -- Macro: unbreak
     With no arguments, unbreaks all currently broken identifiers and returns a list of these formerly broken identifiers.

These are procedures for breaking.  If defmacros are not natively supported by your implementation, these might be more convenient to use.

 -- Function: breakf proc
 -- Function: breakf proc name
     To break, type

          (set! SYMBOL (breakf SYMBOL))

     or

          (set! SYMBOL (breakf SYMBOL 'SYMBOL))

     or

          (define SYMBOL (breakf FUNCTION))

     or

          (define SYMBOL (breakf FUNCTION 'SYMBOL))

 -- Function: unbreakf proc
     To unbreak, type

          (set! SYMBOL (unbreakf SYMBOL))

Tracing
-------

(require 'trace)

This feature provides three ways to monitor procedure invocations:

stack
     Pushes the procedure-name when the procedure is called; pops when it returns.

track
     Pushes the procedure-name and arguments when the procedure is called; pops when it returns.

trace
     Pushes the procedure-name and prints CALL PROCEDURE-NAME ARG1 ... when the procdure is called; pops and prints RETN PROCEDURE-NAME VALUE when the procedure returns.

 -- Variable: debug:max-count
     If a traced procedure calls itself or untraced procedures which call it, stack, track, and trace will limit the number of stack pushes to DEBUG:MAX-COUNT.

 -- Function: print-call-stack
 -- Function: print-call-stack port
     Prints the call-stack to PORT or the current-error-port.

 -- Macro: trace proc1 ...
     Traces the top-level named procedures given as arguments.
 -- Macro: trace
     With no arguments, makes sure that all the currently traced identifiers are traced (even if those identifiers have been redefined) and returns a list of the traced identifiers.

 -- Macro: track proc1 ...
     Traces the top-level named procedures given as arguments.
 -- Macro: track
     With no arguments, makes sure that all the currently tracked identifiers are tracked (even if those identifiers have been redefined) and returns a list of the tracked identifiers.

 -- Macro: stack proc1 ...
     Traces the top-level named procedures given as arguments.
 -- Macro: stack
     With no arguments, makes sure that all the currently stacked identifiers are stacked (even if those identifiers have been redefined) and returns a list of the stacked identifiers.

 -- Macro: untrace proc1 ...
     Turns tracing, tracking, and  off for its arguments.
 -- Macro: untrace
     With no arguments, untraces all currently traced identifiers and returns a list of these formerly traced identifiers.

 -- Macro: untrack proc1 ...
     Turns tracing, tracking, and  off for its arguments.
 -- Macro: untrack
     With no arguments, untracks all currently tracked identifiers and returns a list of these formerly tracked identifiers.

 -- Macro: unstack proc1 ...
     Turns tracing, stacking, and  off for its arguments.
 -- Macro: unstack
     With no arguments, unstacks all currently stacked identifiers and returns a list of these formerly stacked identifiers.

These are procedures for tracing.  If defmacros are not natively supported by your implementation, these might be more convenient to use.

 -- Function: tracef proc
 -- Function: tracef proc name
     To trace, type

          (set! SYMBOL (tracef SYMBOL))

     or

          (set! SYMBOL (tracef SYMBOL 'SYMBOL))

     or

          (define SYMBOL (tracef FUNCTION))

     or

          (define SYMBOL (tracef FUNCTION 'SYMBOL))

 -- Function: untracef proc
     Removes tracing, tracking, or stacking for PROC. To untrace, type

          (set! SYMBOL (untracef SYMBOL))

System Interface
================

If (provided? 'getenv):

 -- Function: getenv name
     Looks up NAME, a string, in the program environment.  If NAME is found a string of its value is returned.  Otherwise, #f is returned.

If (provided? 'system):

 -- Function: system command-string
     Executes the COMMAND-STRING on the computer and returns the integer status code.

Directories
-----------

(require 'directory)

 -- Function: current-directory
     current-directory returns a string containing the absolute file name representing the current working directory.  If this string cannot be obtained, #f is returned.

     If current-directory cannot be supported by the platform, then #f is returned.

 -- Function: make-directory name
     Creates a sub-directory NAME of the current-directory.  If successful, make-directory returns #t; otherwise #f.

 -- Function: directory-for-each proc directory
     PROC must be a procedure taking one argument. Directory-For-Each applies PROC to the (string) name of each file in DIRECTORY.  The dynamic order in which PROC is applied to the filenames is unspecified.  The value returned by directory-for-each is unspecified.

 -- Function: directory-for-each proc directory pred
     Applies PROC only to those filenames for which the procedure PRED returns a non-false value.

 -- Function: directory-for-each proc directory match
     Applies PROC only to those filenames for which (filename:match?? MATCH) would return a non-false value (see Filenames (SLIB)).

          (require 'directory)
          (directory-for-each print "." "[A-Z]*.scm")
          -|
          "Bev2slib.scm"
          "Template.scm"

Transactions
------------

If system is provided by the Scheme implementation, the transact package provides functions for file-locking and file-replacement transactions.

(require 'transact)

     [file transact.txi not included]

CVS
---

(require 'cvs)

     [file cvs.txi not included]

Extra-SLIB Packages
===================

Several Scheme packages have been written using SLIB.  There are several reasons why a package might not be included in the SLIB distribution:

  * Because it requires special hardware or software which is not universal.

  * Because it is large and of limited interest to most Scheme users.

  * Because it has copying terms different enough from the other SLIB packages that its inclusion would cause confusion.

  * Because it is an application program, rather than a library module.

  * Because I have been too busy to integrate it.

Once an optional package is installed (and an entry added to *catalog*, the require mechanism allows it to be called up and used as easily as any other SLIB package.  Some optional packages (for which *catalog* already has entries) available from SLIB sites are:

SLIB-PSD
     is a portable debugger for Scheme (requires emacs editor).

     http://swissnet.ai.mit.edu/ftpdir/scm/slib-psd1-3.tar.gz

     swissnet.ai.mit.edu:/pub/scm/slib-psd1-3.tar.gz

     ftp.maths.tcd.ie:pub/bosullvn/jacal/slib-psd1-3.tar.gz

     ftp.cs.indiana.edu:/pub/scheme-repository/utl/slib-psd1-3.tar.gz

     With PSD, you can run a Scheme program in an Emacs buffer, set breakpoints, single step evaluation and access and modify the program's variables. It works by instrumenting the original source code, so it should run with any R4RS compliant Scheme. It has been tested with SCM, Elk 1.5, and the sci interpreter in the Scheme->C system, but should work with other Schemes with a minimal amount of porting, if at all. Includes documentation and user's manual.  Written by Pertti Kellom\"aki, pk @ cs.tut.fi.  The Lisp Pointers article describing PSD (Lisp Pointers VI(1):15-23, January-March 1993) is available as http://www.cs.tut.fi/staff/pk/scheme/psd/article/article.html

SCHELOG
     is an embedding of Prolog in Scheme. http://www.cs.rice.edu/CS/PLT/packages/schelog/

JFILTER
     is a Scheme program which converts text among the JIS, EUC, and Shift-JIS Japanese character sets. http://www.sci.toyama-u.ac.jp/~iwao/Scheme/Jfilter/index.html

About SLIB
**********

More people than I can name have contributed to SLIB.  Thanks to all of you!

     SLIB SLIBVERSION, released SLIBDATE.

     Aubrey Jaffer <agj @ alum.mit.edu>

     Hyperactive Software -- The Maniac Inside!

     http://swissnet.ai.mit.edu/~jaffer/SLIB.html

Installation
============

There are four parts to installation:

  * Unpack the SLIB distribution.

  * Configure the Scheme implementation(s) to locate the SLIB directory.

  * Arrange for Scheme implementation to load its SLIB initialization file.

  * Build the SLIB catalog for the Scheme implementation.

Unpacking the SLIB Distribution
-------------------------------

If the SLIB distribution is a Linux RPM, it will create the SLIB directory /usr/share/slib.

If the SLIB distribution is a ZIP file, unzip the distribution to create the SLIB directory.  Locate this slib directory either in your home directory (if only you will use this SLIB installation); or put it in a location where libraries reside on your system.  On unix systems this might be /usr/share/slib, /usr/local/lib/slib, or /usr/lib/slib.  If you know where SLIB should go on other platforms, please inform agj @ alum.mit.edu.

Configure Scheme Implementation to Locate SLIB
----------------------------------------------

If the Scheme implementation supports getenv, then the value of the shell environment variable SCHEME_LIBRARY_PATH will be used for (library-vicinity) if it is defined.  Currently, Chez, Elk, MITScheme, scheme->c, VSCM, and SCM support getenv.  Scheme48 supports getenv but does not use it for determining library-vicinity.  (That is done from the Makefile.)

The (library-vicinity) can also be specified from the SLIB initialization file or by implementation-specific means.

Loading SLIB Initialization File
--------------------------------

Check the manifest in README to find a configuration file for your Scheme implementation.  Initialization files for most IEEE P1178 compliant Scheme Implementations are included with this distribution.

You should check the definitions of software-type, scheme-implementation-version, implementation-vicinity, and library-vicinity in the initialization file.  There are comments in the file for how to configure it.

Once this is done, modify the startup file for your Scheme implementation to load this initialization file.

Build New SLIB Catalog for Implementation
-----------------------------------------

When SLIB is first used from an implementation, a file named slibcat is written to the implementation-vicinity for that implementation.  Because users may lack permission to write in implementation-vicinity, it is good practice to build the new catalog when installing SLIB.

To build (or rebuild) the catalog, start the Scheme implementation (with SLIB), then:

     (require 'new-catalog)

The catalog also supports color-name dictionaries.  With an SLIB-installed scheme implementation, type:

     (require 'color-names)
     (make-slib-color-name-db)
     (require 'new-catalog)
     (slib:exit)

Implementation-specific Instructions
------------------------------------

Multiple implementations of Scheme can all use the same SLIB directory. Simply configure each implementation's initialization file as outlined above.

 -- Implementation: SCM
     The SCM implementation does not require any initialization file as SLIB support is already built into SCM.  See the documentation with SCM for installation instructions.

 -- Implementation: VSCM

          From: Matthias Blume <blume @ cs.Princeton.EDU>
          Date: Tue, 1 Mar 1994 11:42:31 -0500

     Disclaimer: The code below is only a quick hack.  If I find some time to spare I might get around to make some more things work.

     You have to provide vscm.init as an explicit command line argument.  Since this is not very nice I would recommend the following installation procedure:

      1. run scheme

      2. (load "vscm.init")

      3. (slib:dump "dumpfile")

      4. mv dumpfile place-where-vscm-standard-bootfile-resides e.g. mv dumpfile /usr/local/vscm/lib/scheme-boot (In this case vscm should have been compiled with flag -DDEFAULT_BOOTFILE='"/usr/local/vscm/lib/scheme-boot"'.  See Makefile (definition of DDP) for details.)

 -- Implementation: Scheme48
     To make a Scheme48 image for an installation under <prefix>,

      1. cd to the SLIB directory

      2. type make prefix=<prefix> slib48.

      3. To install the image, type make prefix=<prefix> install48.  This will also create a shell script with the name slib48 which will invoke the saved image.

 -- Implementation: PLT Scheme
 -- Implementation: DrScheme
 -- Implementation: MzScheme

     The init.ss file in the _slibinit_ collection is an SLIB initialization file.

     To use SLIB in MzScheme, set the SCHEME_LIBRARY_PATH environment variable to the installed SLIB location; then invoke MzScheme thus:

     mzscheme -f ${SCHEME_LIBRARY_PATH}DrScheme.init

 -- Implementation: MIT Scheme
     scheme -load ${SCHEME_LIBRARY_PATH}mitscheme.init

 -- Implementation: Guile
     guile -l ${SCHEME_LIBRARY_PATH}guile.init

Porting
=======

If there is no initialization file for your Scheme implementation, you will have to create one.  Your Scheme implementation must be largely compliant with IEEE Std 1178-1990, Revised^4 Report on the Algorithmic Language Scheme, or Revised^5 Report on the Algorithmic Language Scheme in order to support SLIB.   (If you are porting a Revised^3 Report on the Algorithmic Language Scheme implementation, then you will need to finish writing sc4sc3.scm and load it from your initialization file.)

Template.scm is an example configuration file.  The comments inside will direct you on how to customize it to reflect your system. Give your new initialization file the implementation's name with .init appended.  For instance, if you were porting foo-scheme then the initialization file might be called foo.init.

Your customized version should then be loaded as part of your scheme implementation's initialization.  It will load require.scm from the library; this will allow the use of provide, provided?, and require along with the vicinity functions (these functions are documented in the section Require). The rest of the library will then be accessible in a system independent fashion.

Please mail new working configuration files to agj @ alum.mit.edu so that they can be included in the SLIB distribution.

Coding Guidelines
=================

All library packages are written in IEEE P1178 Scheme and assume that a configuration file and require.scm package have already been loaded.  Other versions of Scheme can be supported in library packages as well by using, for example, (provided? 'rev3-report) or (require 'rev3-report) (see Require).

The module name and : should prefix each symbol defined in the package.  Definitions for external use should then be exported by having (define foo module-name:foo).

Code submitted for inclusion in SLIB should not duplicate routines already in SLIB files.  Use require to force those library routines to be used by your package.  Care should be taken that there are no circularities in the requires and loads between the library packages.

Documentation should be provided in Emacs Texinfo format if possible, But documentation must be provided.

Your package will be released sooner with SLIB if you send me a file which tests your code.  Please run this test before you send me the code!

Modifications
-------------

Please document your changes.  A line or two for ChangeLog is sufficient for simple fixes or extensions.  Look at the format of ChangeLog to see what information is desired.  Please send me diff files from the latest SLIB distribution (remember to send diffs of slib.texi and ChangeLog).  This makes for less email traffic and makes it easier for me to integrate when more than one person is changing a file (this happens a lot with slib.texi and *.init files).

If someone else wrote a package you want to significantly modify, please try to contact the author, who may be working on a new version.  This will insure against wasting effort on obsolete versions.

Please do not reformat the source code with your favorite beautifier, make 10 fixes, and send me the resulting source code.  I do not have the time to fish through 10000 diffs to find your 10 real fixes.

Copyrights
==========

This section has instructions for SLIB authors regarding copyrights.

Each package in SLIB must either be in the public domain, or come with a statement of terms permitting users to copy, redistribute and modify it. The comments at the beginning of require.scm and macwork.scm illustrate copyright and appropriate terms.

If your code or changes amount to less than about 10 lines, you do not need to add your copyright or send a disclaimer.

Putting code into the Public Domain
-----------------------------------

In order to put code in the public domain you should sign a copyright disclaimer and send it to the SLIB maintainer.  Contact agj @ alum.mit.edu for the address to mail the disclaimer to.

     I, NAME, hereby affirm that I have placed the software package NAME in the public domain.

     I affirm that I am the sole author and sole copyright holder for the software package, that I have the right to place this software package in the public domain, and that I will do nothing to undermine this status in the future.

     SIGNATURE AND DATE

This wording assumes that you are the sole author.  If you are not the sole author, the wording needs to be different.  If you don't want to be bothered with sending a letter every time you release or modify a module, make your letter say that it also applies to your future revisions of that module.

Make sure no employer has any claim to the copyright on the work you are submitting.  If there is any doubt, create a copyright disclaimer and have your employer sign it.  Mail the signed disclaimer to the SLIB maintainer.  Contact agj @ alum.mit.edu for the address to mail the disclaimer to.  An example disclaimer follows.

Explicit copying terms
----------------------

If you submit more than about 10 lines of code which you are not placing into the Public Domain (by sending me a disclaimer) you need to:

  * Arrange that your name appears in a copyright line for the appropriate year.   Multiple copyright lines are acceptable.

  * With your copyright line, specify any terms you require to be different from those already in the file.

  * Make sure no employer has any claim to the copyright on the work you are submitting.  If there is any doubt, create a copyright disclaimer and have your employer sign it.  Mail the signed disclaim to the SLIB maintainer.  Contact agj @ alum.mit.edu for the address to mail the disclaimer to.

Example: Company Copyright Disclaimer
-------------------------------------

This disclaimer should be signed by a vice president or general manager of the company.  If you can't get at them, anyone else authorized to license out software produced there will do.  Here is a sample wording:

     EMPLOYER Corporation hereby disclaims all copyright interest in the program PROGRAM written by NAME.

     EMPLOYER Corporation affirms that it has no other intellectual property interest that would undermine this release, and will do nothing to undermine it in the future.

     SIGNATURE AND DATE,
     NAME, TITLE, EMPLOYER Corporation

Procedure and Macro Index
*************************

This is an alphabetical list of all the procedures and macros in SLIB.

Variable Index
**************

This is an alphabetical list of all the global variables in SLIB.