This is librep.info, produced by makeinfo version 4.6 from librep.texi. INFO-DIR-SECTION Programming Languages START-INFO-DIR-ENTRY * librep: (librep). A flexible Lisp environment END-INFO-DIR-ENTRY This is Edition 1.2, last updated 8 September 2000, of `The librep Manual', for librep, Version 0.13. Copyright 1999-2000 John Harper. 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.  File: librep.info, Node: Top, Next: Copying, Prev: (dir), Up: (dir) This document describes `librep', a simple, but powerful, Lisp dialect intended both as an embedded extension language, and as a stand-alone programming language. This is Edition 1.2 of its documentation, last updated 8 September 2000 for librep version 0.13. * Menu: * Copying:: Distribution conditions * Introduction:: Brief introduction to librep * Invocation:: How to start the interpreter * The language:: The Lisp dialect implemented * The REPL:: The interactive environment * librep Internals:: Embedding librep in other programs * Reporting bugs:: How to contact the maintainers * News:: History of user-visible changes * Function index:: Menu of all documented functions * Variable index:: All variables which have been mentioned * Concept index:: Main index, references to all sections  File: librep.info, Node: Copying, Next: Introduction, Prev: Top, Up: Top Copying ******* `librep' is distributed under the terms of the GNU General Public License, this basically means that you can give it to anyone for any price as long as full source code is included; you also have the right to distribute modified copies in the same way. For the actual legalese see the file `COPYING' in the distribution (or *note (emacs)Copying::). In case it isn't obvious, scripts written to use librep are not considered derived works, and therefore may be licensed however the author wishes. However, the ability of scripts to dynamically load external libraries may complicate this situation. The distribution includes the following code from other packages: * Henry Spencer's `regexp' implementation, with many modifications. This is distributed under the terms of his copyright, see the file `src/README.regexp' in the distribution. * The public domain `sdbm' database library by Ozan Yigit. * The backquote package from Emacs version 19, written by Rick Sladkey. * The GNU `gettext' implementation for internationalized message catalogues. Be aware that there is absolutely NO WARRANTY for this program, you use it at your own risk. Obviously I hope there are no bugs, but I make no promises regarding the reliability of this software.  File: librep.info, Node: Introduction, Next: Invocation, Prev: Copying, Up: Top Introduction ************ `librep' is a dialect of Lisp, designed to be used both as an extension language for applications and as a general purpose programming language. It was originally written to be mostly-compatible with Emacs Lisp, but has subsequently diverged markedly. Its aim is to combine the best features of Scheme and Common Lisp and provide an environment that is comfortable for implementing both small and large scale systems. It tries to be a "pragmatic" programming language. The author has used `librep' in its various forms in many projects since 1993. This includes two large programs which use it as an extension language, and many stand-alone programs. `rep' stands for "Read, Eval, Print", the three main components of any Lisp system. Some of the features of `librep' are: * Lexically scoped (with special variables from CL) * Clean module system * Tail-call elimination * Compiles to byte-code * First-class continuations * Uses GNU MP for fast bignums/rationals * Most Emacs Lisp functions, with others inspired by Common Lisp and various Scheme implementations * Mostly-Perl-like regular expressions * Spawn and control subprocesses * Dynamically loads shared libraries (a.k.a. "plugins") * Extensible type, I/O, and file handling  File: librep.info, Node: Invocation, Next: The language, Prev: Introduction, Up: Top Invocation ********** The `rep' program may be used to launch the stand-alone `librep' environment: usage: rep [REP-OPTIONS...] [SCRIPT [SCRIPT-OPTIONS...]] Where REP-OPTIONS may be any of the following: `--init FILE' Use FILE to boot the Lisp system from, instead of `init.jl'. `--version' Print the current version number and exit `--batch' Tell the interpreter that it is running non-interactively, this reduces the number of messages output to the console `--interp' Interpreted mode. Never load compiled Lisp files: this can be useful when using the debugger. `--no-rc' Don't load the user's `~/.reprc' script, or the `site-init.jl' script `-f FUNCTION' Invoke the Lisp function FUNCTION (with no arguments) `-l SCRIPT' Try to load the Lisp file SCRIPT, this is equivalent to evaluating the form `(load "SCRIPT")'. `-q' Terminate the Lisp process and exit. If SCRIPT is given, it names the Lisp file to load, equivalent to the `-l' option, except that `--batch-mode' is implied. Any SCRIPT-OPTIONS will be made available to the script (in the `command-line-args' variable). After any arguments have been processed a banner message will be displayed before entering an interactive read-eval-print loop, unless `--batch-mode' was specified, in which case the interpreter exits. The read-eval-print loop simply reads complete Lisp forms (*note The Lisp Reader::), evaluates them, before printing the result back to the console; this continues ad infinitum, or until you force an EOF (i.e. enter `C-d'). Implicitly Interpreting `rep' Scripts ..................................... The `rep' interpreter also supports automatic invocation of scripts, using the oeprating system's support for `#!' interpreter invocation (i.e. if the first line of an executable text file contains `#! PROG', the program PROG is used to execute the script. However there is a problem with this method, in that the `PATH' environment variable is not searched for the location of the interpreter, and thus the full file name of the interpreter program must be hard-coded into the script. To work around this problem `rep' supports a slightly different method of invocation. If the first two characters of a loaded Lisp file are `#!', then everything is treated as a comment until the first occurrence of the string `!#'. This allows the first part of the script to be executed as a shell script invoking the `rep' interpreter. What this means, is that you want to put something like the following at the start of any scripts you want to execute implicitly (and `chmod +x' the file as well): #!/bin/sh exec rep "$0" "$@" !# ;; Lisp code follows...  File: librep.info, Node: The language, Next: The REPL, Prev: Invocation, Up: Top The language ************ This chapter of the manual is a full guide to the librep Lisp programming language, including documentation for most of the built-in functions. * Menu: * Intro:: Introduction and Lisp conventions Fundamental data types. * Data Types:: Data types and values in Lisp * Numbers:: Numeric representations and functions * Sequences:: Ordered sequences of data values * Symbols:: Symbols are uniquely named objects The core language. * Evaluation:: Evaluating expressions * Variables:: Symbols represent named variables * Functions:: The building blocks of Lisp programs * Macros:: User-defined control structures * Definitions:: Block-structured definitions * Modules:: Scoping for "global" definitions * Control Structures:: Conditionals, loops, etc... * Threads:: Multi-threaded programs * Loading:: Programs are stored in files * Compiled Lisp:: Making programs run faster Data structures and I/O. * Datums:: Low-level data type definition * Queues:: FIFO queue type * Records:: Defining structured data types * Hash Tables:: Efficient table lookups * Guardians:: Protecting objects from GC * Streams:: Data sinks and sources; character streams * Hooks:: Hooks promote extensibility * Files:: Manipulating files in the filing system * Processes:: launch and control subprocesses when running under Unix Miscellaneous features. * Regular Expressions:: Matching regular expressions * Time and Date:: Manipulating time and date * i18n:: Internationalisation * System Information:: Getting details about the host * User Information:: The name of the user * Environment Variables:: Reading and writing the environment * String Functions:: Misc string manipulation * Sleeping:: Waiting for a period of time * Beeping:: Making a ding! sound * Messages:: Writing to the console * Command Line Options:: Retrieving command line arguments * Shell Commands:: Executing shell commands * Timers:: Asynchronous timers * Debugging:: How to debug Lisp programs * Tips:: General ideas for `librep' programming This manual still fails to document the following functions: default-boundp, default-value, recursive-edit, regexp-cache-control, sdbm-close, sdbm-delete, sdbm-error, sdbm-fetch, sdbm-firstkey, sdbm-nextkey, sdbm-open, sdbm-rdonly, sdbm-store, sdbmp, set-default, setq-default,  File: librep.info, Node: Intro, Next: Data Types, Up: The language Introduction ============ As you have probably gathered by now, `librep' provides a dialect of the Lisp programming language--a dialect originally inspired by Emacs Lisp, but later adapted to include many features from various Scheme implementations and Common Lisp. The language dialect aims to be convenient for both extending applications and writing large stand-alone programs. All programs written using only the information in this manual should be compatible with future revisions of `librep'. This following sections explain some of the most important Lisp concepts and the conventions I've used in this manual. * Menu: * nil and t:: Boolean values in Lisp * The Lisp Reader:: Basic program structure * Notation:: Special glyphs used * Descriptions:: How functions and variables are documented  File: librep.info, Node: nil and t, Next: The Lisp Reader, Up: Intro nil and t --------- In the rep Lisp dialect there is a single data value representing boolean "false"--the empty list, written as `()'. All other values are considered "not-false", i.e. "true". By convention the constants `nil' and `t' are used to represent the canonical boolean values. The constant variable `nil' evaluates to the empty list (i.e. "false"), while `t' evaluates to itself (i.e. not-"false", therefore "true"). Reiterating, all of the conditional operations regard _anything_ which is not `()' as being true (i.e. non-false). The actual symbol `t' should be used where a true boolean value is explicitly stated, to increase the clarity of the code. So, `()', and its alias `nil', represent both the empty list and boolean falsehood. Most Lisp programmers write `()' where its value as a list should be emphasized, and `nil' where its value as boolean false is intended. Although neither of these values need be quoted (*note Quoting::), most programmers will quote the empty list to emphasize that it is a constant value. However `nil' should not be quoted, doing so would produce the _symbol_ `nil', not boolean falsehood. For example: (append '() '()) => () ;Emphasize use of empty lists (not nil) => t ;Emphasize use as boolean false (get 'nil 'color) ;Use the symbol `nil' When a function is said to "return false", it means that it returns the false boolean value, i.e. the empty list. When a function is said to "return true", this means that any non-false value is returned.  File: librep.info, Node: The Lisp Reader, Next: Notation, Prev: nil and t, Up: Intro The Lisp Reader --------------- Lisp programs and functions are stored internally as Lisp data objects, the Lisp Reader is the mechanism that translates from textual descriptions of Lisp objects to the internal data structures representing them. The Lisp Reader is the collection of internal functions accessed by the `read' Lisp function. It reads a character at a time from an input stream until a whole Lisp object has been parsed. *Note Data Types::.  File: librep.info, Node: Notation, Next: Descriptions, Prev: The Lisp Reader, Up: Intro Notation -------- Wherever an example of evaluating a Lisp form is shown it will be formatted like this, (+ 1 2) => 3 The glyph `=>' is used to show the computed value of a form. (1) When two forms are shown as being exactly equivalent to one another the glyph `==' is used, for example, (car some-variable) == (nth 0 some-variable) Evaluating some forms result in an error being signalled, this is denoted by the `error-->' glyph. (open-file "/tmp/foo" 'read) error--> File error: No such file or directory, /tmp/foo ---------- Footnotes ---------- (1) In this case the list `(+ 1 2)' (i.e. the list containing three elements, the symbol `+' and, the numbers 1 and 2), represents a function application. The first element in the list is the name of the function to be called, all other elements are the arguments to apply to it. Since the `+' function adds a series of numbers, the above function call is actually performing the computation `1 + 2'.  File: librep.info, Node: Descriptions, Prev: Notation, Up: Intro Descriptions ------------ In this document the simplest type of descriptions are those defining variables (*note Variables::), they look something like: - Variable: grains-of-sand This imaginary variable contains the number of grains of sand in a one-mile long stretch of an averagely sandy beach. Hooks (*note Hooks::) are also described in this format, the only difference is that `Variable:' is replaced by `Hook:'. Functions (*note Functions::) and macros (*note Macros::) have more complex descriptions; as well as the name of the object being described, they also have a list of parameters which the object will accept. Each parameter in the list is named and may be referred to in the body of the description. Three keyword parameters may also be used: `#!optional', `#!key' and `#!rest'. They have the same meaning as when used in the lambda-list of a function definition (*note Lambda Expressions::). That is, `#!optional' means that all further parameters are optional, and `#!rest' means that the following parameter actually receives a list of any unused argument values. An example function definition follows. - Function: useless-function first `#!optional' second `#!rest' tail This function returns a list consisting of the values SECOND (when undefined the number 42 is used), all the items in the list TAIL and FIRST. (useless-function 'foo 'bar 'xyz 20) => (bar xyz 20 foo) (useless-function '50) => (42 50) Macros and interactive commands are defined in the same way with `Macro:' or `Command:' replacing `Function:'. Special forms (*note Special Forms::) are described similarly to functions except that the argument list is formatted differently, since special forms are, by definition, more flexible in how they treat their arguments. Optional values are enclosed in square brackets (`[OPTIONAL-ARG]') and three dots (`REPEATED-ARG...') indicate where zero or more arguments are allowed.  File: librep.info, Node: Data Types, Next: Numbers, Prev: Intro, Up: The language Data Types ========== The way that data is represented in Lisp is fundamentally different to languages such as C or Fortran. In Lisp each piece of data (or "value") has two basic attributes: the data and the _type_ of the data. This means that type checking is performed at run-time on the actual data itself, not at compile-time on the "variable" holding the data. Also, there are no "pointers" in Lisp. As in the Java programming language, all values are references to data structures, with each actual data structure (or "Lisp Object") being able to have as many values referring to it concurrently as necessary. Because of this lack of pointers, there can be no memory-leakage in Lisp--when an object has no more extant references, it is automatically deallocated (*note Garbage Collection::). Most Lisp objects are a member of one of the primitive types; these are types built into the Lisp system and can represent things like strings, numbers, cons cells, vectors, etc... Other primitive types may be defined at run-time. More complex objects may be constructed from these primitive types, for example a vector of three elements could be regarded as a type `triple' if necessary. In general, each separate type provides a predicate function which returns true when applied to an object of its own type. Finally, one of the most important differences between Lisp and other languages is that there is no distinction between programs and data. But this will be explained later. * Menu: * Types Summary:: List of the most common types * Read Syntax:: Some types can be made from source code * Printed Representation:: All types can be printed * Equality Predicates:: How to test two objects for equality * Comparison Predicates:: Comparing two objects as scalars * Type Predicates:: Each type has a predicate defining it * Garbage Collection:: Reusing memory from stale objects  File: librep.info, Node: Types Summary, Next: Read Syntax, Up: Data Types Types Summary ------------- Each separate data type is documented in its own section, this is a just a summary of the more common types. "Numbers" Numbers: fixnums, bignums, rationals and floats. *Note Numbers::. "Cons cell" An object referring to two other Lisp objects. *Note Cons Cells::. "List" A sequence of objects, in Lisp lists are not primitive types, instead they are made by chaining together Cons cells. *Note Lists::. "Vector" A one-dimensional array of objects. *Note Vectors::. "String" A vector of characters. *Note Strings::. "Array" An ordered sequence of objects which can be accessed in constant time, either a vector or a string. *Note Sequences::. "Sequence" An ordered sequence of objects, either a list or an array. *Note Sequences::. "Symbol" A symbol is a named object; they are used to provide named variables and functions. *Note Symbols::. "File" A link to a notional file in the filing system. This file may be in the local filing system, or on a FTP server, or wherever. *Note Files::. "Process" An object through which processes may be created and controlled. *Note Processes::. "Stream" Serial data sinks and sources. These may include files, functions, and processes. *Note Streams::. "Void" The empty type, only used in symbols to represent an undefined value. Note that this is not the same as `()', which is the empty list, or false truth value.  File: librep.info, Node: Read Syntax, Next: Printed Representation, Prev: Types Summary, Up: Data Types Read Syntax ----------- As previously noted the Lisp reader translates textual descriptions of Lisp objects into the object they describe (source files are simply descriptions of objects). However, not all data types can be created in this way: in fact the only types which can are numbers, strings, symbols, cons cells (or lists) and vectors, all others have to be created by calling functions. Single line comments are introduced by a semi-colon character (`;'). Whenever the Lisp reader encounters a semi-colon where it's looking for the read syntax of a new Lisp object it will discard the rest of the line of input. Block comments are also supported, introduced by the string `#|' and terminated by `|#'. *Note Comment Styles::. The "read syntax" of an object is the string which when given to the reader as input will produce the object. The read syntax of each type of object is documented in that type's main section of this manual but here is a small summary of how to write each type. Numbers A number is number written as an integer--decimal, octal (when the number is preceded by `#o') or hexadecimal (when the number is preceded by `#x')--or a decimal rational or floating point value. An optional minus sign may be the first character in a number. Some examples are, 42 => 42 #o177 => 127 #x-ff => -255 3/2 => 3/2 1.23 => 1.23 Strings The read syntax of a string is simply the string with a double-quote character (`"') at each end, for more details see *Note Strings::. "This is a string" Cons cells A cons cell is written in what is known as "dotted pair notation", an opening left-parenthesis, followed by the read syntax of the first object, followed by a dot, then the second object, and finally a closing right-parenthesis. For example: ("car" . "cdr") Lists The syntax of a list is similar to a cons cell, but the dot is removed and zero or more objects may be written: (0 1 2 3) ("foo" ("bar" "baz") 100) The second example is a list of three elements, a string, an inner list and a number. Vectors The read syntax of a vector is similar to that of a list, but with square brackets instead of parentheses, [0 1 2 3] Symbols The read syntax of a symbol is its name, for example the read syntax of the symbol called `my-symbol' is, my-symbol  File: librep.info, Node: Printed Representation, Next: Equality Predicates, Prev: Read Syntax, Up: Data Types Printed Representation ---------------------- As well as translating textual descriptions to Lisp objects, the process may be reversed, converting a value back to a textual description. The resulting text is known as the "printed representation" of the object, and will usually be very similar to the read syntax of the object (*note Read Syntax::). Objects which do not have a read syntax _do_ have a printed representation, it will normally be of the form, # where the RELEVANT-TEXT is object-dependent and usually describes the object and its contents. The reader will signal an error if it encounters a description of an object in the format `#<...>'.  File: librep.info, Node: Equality Predicates, Next: Comparison Predicates, Prev: Printed Representation, Up: Data Types Equality Predicates ------------------- - Function: eq arg1 arg2 Returns true when ARG1 and ARG2 refer to the same object. Two objects are the same when they occupy the same place in memory and hence modifying one object would alter the other. The following Lisp fragments may illustrate this, (eq "foo" "foo") ;the objects are distinct => () (eq t t) ;the same object -- the symbol `t' => t Note that the result of `eq' is undefined when called on two integer objects with the same value, see `eql'. - Function: equal arg1 arg2 The function `equal' compares the structure of the two objects ARG1 and ARG2. If they are considered to be equivalent then returns true, otherwise returns false. (equal "foo" "foo") => t (equal 42 42) => t (equal 42 0) => () (equal '(x . y) '(x . y)) => t - Function: eql arg1 arg2 This function is a cross between `eq' and `equal': if ARG1 and ARG2 are both numbers then the value of these numbers are compared. Otherwise it behaves in exactly the same manner as `eq' does. (eql 3 3) => t (eql 1 2) => () (eql "foo" "foo") => () (eql 'x 'x) => t  File: librep.info, Node: Comparison Predicates, Next: Type Predicates, Prev: Equality Predicates, Up: Data Types Comparison Predicates --------------------- These functions compare their two arguments in a scalar fashion, the arguments may be of any type but the results are only meaningful for numbers, strings (ASCII values of each byte compared until a non-matching pair is found then those two values are compared as numbers) and cons cells (cars compared before cdrs). Unlike the `eql' function, inexact and exact numbers will be compared by first coercing the exact number to be inexact. - Function: = arg1 arg2 arg3 ... argn Returns true if all arguments represent the same value. - Function: /= arg1 arg2 arg3 ... argn Returns true if no two arguments represent the same value. - Function: > arg1 arg2 arg3 ... argn Returns true when ARG1 is `greater than' ARG2, and ARG2 is greater than ARG3, and so on, upto ARGN. - Function: >= arg1 arg2 arg3 ... argn Similar to `>', but for the "greater than or equal to" relation. - Function: < arg1 arg2 arg3 ... argn Similar to `>', but for the "less than" relation. - Function: <= arg1 arg2 arg3 ... argn Similar to `>', but for the "less than or equal to" relation. There are two related functions for finding the maximum or minimum of a sequence of values. - Function: max #!rest args Return the maximum value from the list of ARGS. When comparing numbers, any inexact arguments cause the result to be inexact. - Function: min #!rest args Return the minimum value from the list of ARGS. When comparing numbers, any inexact arguments cause the result to be inexact.  File: librep.info, Node: Type Predicates, Next: Garbage Collection, Prev: Comparison Predicates, Up: Data Types Type Predicates --------------- Each type has a corresponding predicate which defines the objects which are members of that type. Each predicate function has a single parameter, if that parameter is of the correct type it returns true. `integerp', `numberp', `null', `consp', `listp', `vectorp', `subrp', `functionp', `sequencep', `stringp', `symbolp', `processp', `filep'. The documentation for these functions is with the documentation for the relevant type.  File: librep.info, Node: Garbage Collection, Prev: Type Predicates, Up: Data Types Garbage Collection ------------------ In Lisp, data objects are used very freely; a side effect of this is that it is not possible to (easily) know when an object is "stale", that is, no references to it exist and it can therefore be reused. The "garbage collector" is used to overcome this problem; whenever enough memory has been allocated to make it worthwhile, evaluation stops and the garbage collector works its way through memory deciding which objects may still be referenced, and which are stale. The stale objects are then recorded as being available for reuse and evaluation continues. (But *note Guardians::) - Function: garbage-collect Runs the garbage collector, usually this function doesn't need to be called manually. - Variable: garbage-threshold The number of bytes of data that must have been allocated since the last garbage collection before evaluation pauses and the garbage collector is invoked. Its default value is about 100K. - Variable: idle-garbage-threshold When the input loop is idle (due to a lack of input), this is the number of bytes of data that must have been allocated since the garbage collection, for another collection to be triggered. This is usually set to a lot less than `garbage-threshold' since the small delay caused by garbage collection is unnoticeable if the system is already idle. - Variable: after-gc-hook A hook (*note Normal Hooks::) called immediately after each invocation of the garbage collector.  File: librep.info, Node: Numbers, Next: Sequences, Prev: Data Types, Up: The language Numbers ======= `Librep' distinguishes between numbers that are represented exactly and numbers that may not be. This is similar to the Scheme dialect of Lisp. Quoting from the Scheme standard: ... numbers are either _exact_ or _inexact_. A number is exact if it was written as an exact constant or was derived from exact numbers using only exact operations. A number is inexact if it was written as an inexact constant, if it was derived using inexact ingredients, or if it was derived using inexact operations. Thus inexactness is a contagious property of a number. Exact numbers include both integers and rational numbers, there is no theoretical limit to the range of the values that may be represented (1). Inexact numbers are currently implemented using double precision floating point values. The read syntax of any number is: `[PFX...][SGN]DATA...', where the optional SGN is one of the characters `-' or `+', DATA is the representation of the number, and PFX is zero or more of the following prefix strings: `#b' `#B' Integers are described in binary, `#o' `#O' Integers are in octal, `#d' `#D' Integers are in decimal (the default), `#x' `#X' Integers are in hexadecimal, `#e' `#E' Coerce the number to an exact representation after parsing it, `#i' `#I' Coerce to an inexact representation. The representation of an integer is simply the digits representing that integer, in the radix chosen by any given prefix (defaults to decimal). Examples of valid integer read syntaxes for the number 42 could be `42', `#x2a', `#o52', `#o+52', ... The representation of a rational number is two sequences of digits, separated by a `/' character. For example, `3/2' represents the rational number three divided by two. Inexact numbers are parsed from one of two representations: decimal point form, which is simply a decimal number containing a decimal point, and exponential form, which is a decimal number followed by the letter `e' and a decimal exponent multiplying the first part of the number by that power of ten. For example, `10.0', `10.' and `1e1' all read as the inexact number ten. Note that the radix prefixes currently have no effect when parsing inexact numbers, decimal is used exclusively. An integer's printed representation is simply the number printed in decimal with a preceding minus sign if it is negative. Rational numbers are printed as two integers separated by a `/' character. Inexact numbers are printed in their decimal form. - Function: numberp object Returns true if OBJECT is a number. * Menu: * Arithmetic Functions:: * Integer Functions:: * Rational Functions:: * Real Number Functions:: * Mathematical Functions:: * Bitwise Functions:: * Numeric Predicates:: * Random Numbers:: * Characters:: ---------- Footnotes ---------- (1) However, depending on implementation restrictions, very large integers may be coerced to an inexact representation.  File: librep.info, Node: Arithmetic Functions, Next: Integer Functions, Up: Numbers Arithmetic Functions -------------------- There are a number of functions which perform arithmetic operations on numbers, they take a varying number of values as their arguments returning a new number as their result. When given only exact arguments, an exact result will be returned. - Function: + number1 #!rest numbers This functions adds its arguments then returns their sum. - Function: - number1 #!rest numbers If this function is just given one argument (NUMBER1) that number is negated and returned. Otherwise each of NUMBERS is subtracted from a running total starting with the value of NUMBER1. (- 20) => -20 (- 20 10 5) => 5 - Function: * number1 #!rest numbers This function multiplies its arguments then returns the result. - Function: / number1 #!rest numbers This function performs division, a running-total (initialised from NUMBER1 is successively divided by each of NUMBERS then the result is returned. (/ 100 2) => 50 (/ 200 2 5) => 20 (/ 3 2) => 3/2 (/ 3.0 2) => 1.5 - Function: 1+ number This function returns the result of adding one to NUMBER. (1+ 42) => 43 - Function: 1- number Returns NUMBER minus one.  File: librep.info, Node: Integer Functions, Next: Rational Functions, Prev: Arithmetic Functions, Up: Numbers Integer Functions ----------------- The functions described in this section all operate on, and return, integer values. - Function: quotient dividend divisor Return the integer part of dividing DIVIDEND by DIVISOR. - Function: remainder dividend divisor Returns the integer remainder from dividing the DIVIDEND by DIVISOR. The remainder is either zero or has the same sign as DIVIDEND. - Function: modulo dividend divisor - Function: mod dividend divisor Return the value of DIVIDEND modulo DIVISOR. Unlike the `remainder' function the `modulo' function always has the sign of the DIVISOR, not of the DIVIDEND - Function: gcd args... Returns the greatest common divisor of the integers ARGS... If no arguments are given, returns zero. - Function: lcm args... Return the lowest common multiple of the integers ARGS... If no arguments are given, returns one.  File: librep.info, Node: Rational Functions, Next: Real Number Functions, Prev: Integer Functions, Up: Numbers Rational Functions ------------------ These functions operate on rational numbers. - Function: numerator x Returns the exact numerator of X. - Function: denominator x Returns the exact denominator of X. - Function: exact->inexact x Returns an inexact version of rational number X.  File: librep.info, Node: Real Number Functions, Next: Mathematical Functions, Prev: Rational Functions, Up: Numbers Real Number Functions --------------------- - Function: abs x Returns the magnitude of X. - Function: floor x Round X downwards to the nearest integer less than or equal to X. - Function: ceiling x Round X upwards to the nearest integer less than or equal to X. - Function: truncate x Round X to the nearest integer between X and zero. - Function: round x Round X to the nearest integer. Halfway cases are rounded to the nearest even integer. - Function: inexact->exact x Returns an exact representation of X. This may involve a loss of accuracy.  File: librep.info, Node: Mathematical Functions, Next: Bitwise Functions, Prev: Real Number Functions, Up: Numbers Mathematical Functions ---------------------- - Function: exp x Return `e' (the base of natural logarithms) raised to the power X. - Function: log x Return the natural logarithm of X. An arithmetic error is signalled if X is less than zero. - Function: sin x Return the sine of angle X; x is in terms of radians. - Function: cos x Return the cosine of angle X. - Function: tan x Return the tangent of angle X. - Function: asin x Return the arc sine of X (the value whose sine is X), in radians. - Function: acos x Return the arc cosine of X. - Function: atan x Return the arc tangent of X. - Function: sqrt x Return the non-negative square root of X. Currently, if X is negative, an arithmetic error is signalled. - Function: expt x y Returns X raised to the power Y. If X is negative and Y is a non-integer, then an arithmetic error is signalled (mathematically should return a complex number).  File: librep.info, Node: Bitwise Functions, Next: Numeric Predicates, Prev: Mathematical Functions, Up: Numbers Bitwise Functions ----------------- These functions operate on the bit string which an integer represents, assuming a two's complement representation. - Function: lsh number count This function shifts the integer NUMBER COUNT bits to the left, if COUNT is negative NUMBER is shifted to the right instead. (lsh 1 8) => 256 (lsh 256 -8) => 1 - Function: logand number1 #!rest numbers This function uses a bit-wise logical `and' operation to combine all its arguments (there must be at least one argument). (logand 15 8) => 8 (logand 15 7 20) => 4 - Function: logior number1 #!rest numbers Uses a bit-wise logical `inclusive-or' to combine all its arguments (there must always be at least one argument). (logior 1 2 4) => 7 - Function: logxor number1 #!rest numbers Uses a bitwise logical `exclusive-or' to combine all its arguments (there must be at least one). (logxor 7 3) => 4 - Function: lognot number This function inverts all the bits in NUMBER. (lognot 0) => -1 (lognot 2) => -3 (lognot -1) => 0  File: librep.info, Node: Numeric Predicates, Next: Random Numbers, Prev: Bitwise Functions, Up: Numbers Numeric Predicates ------------------ For the documentation of the functions `=', `/=', `>', `<', `>=', `<=', `max' and `min', see *Note Comparison Predicates::. - Function: exactp object Returns true when OBJECT is an exact number. - Function: inexactp object Returns true when OBJECT is an inexact number. - Function: integerp object Returns true when OBJECT is an integer. - Function: rationalp object Returns true when OBJECT is a rational number (including integers). - Function: realp object Returns true when OBJECT is a real number. - Function: oddp x Return true if X is an odd number. - Function: evenp x Return true if X is an even number. - Function: positivep x Return true if X is a number greater than zero. - Function: negativep x Return true if X is a number less than zero. - Function: zerop x Returns true if X is equal to zero.  File: librep.info, Node: Random Numbers, Next: Characters, Prev: Numeric Predicates, Up: Numbers Pseudo-Random Numbers --------------------- The `random' function allows pseudo-random numbers to be generated. - Function: random #!optional limit Return a pseudo-random number between zero and LIMIT-1 inclusive. If LIMIT is undefined, it is taken as being the largest positive integer representable in a fixnum. Calling `random' with LIMIT equal to the symbol `t' seeds the generator with the current time of day.  File: librep.info, Node: Characters, Prev: Random Numbers, Up: Numbers Characters ---------- In `librep' characters are stored in integers. Their read syntax is a question mark followed by the character itself, which may be an escape sequence introduced by a backslash. For details of the available escape sequences see *Note Strings::. ?a => 97 ?\n => 10 ?\177 => 127 - Function: alpha-char-p character This function returns true when CHARACTER is one of the alphabetic characters. (alpha-char-p ?a) => t - Function: upper-case-p character When CHARACTER is one of the upper-case characters this function returns true. - Function: lower-case-p character Returns true when CHARACTER is lower-case. - Function: digit-char-p character This function returns true when CHARACTER is one of the decimal digit characters. - Function: alphanumericp character This function returns true when CHARACTER is either an alphabetic character or a decimal digit character. - Function: space-char-p character Returns true when CHARACTER is a white-space character (space, tab, newline or form feed). - Function: char-upcase character This function returns the upper-case equivalent of CHARACTER. If CHARACTER is already upper-case or has no upper-case equivalent it is returned unchanged. (char-upcase ?a) => 65 ;`A' (char-upcase ?A) => 65 ;`A' (char-upcase ?!) => 33 ;`!' - Function: char-downcase character Returns the lower-case equivalent of the character CHARACTER.  File: librep.info, Node: Sequences, Next: Symbols, Prev: Numbers, Up: The language Sequences ========= Sequences are ordered groups of objects, there are several primitive types which can be considered sequences, each with their pros and cons. A sequence is either an array or a list, where an array is either a vector or a string. - Function: sequencep object This function returns true if OBJECT is a sequence. * Menu: * Cons Cells:: An ordered pair of two objects * Lists:: Chains of cons cells * Vectors:: A chunk of memory holding a number of objects * Strings:: Strings are efficiently-stored vectors * Array Functions:: Accessing elements in vectors and strings * Sequence Functions:: These work on any type of sequence  File: librep.info, Node: Cons Cells, Next: Lists, Up: Sequences Cons Cells ---------- A "cons cell" is an ordered pair of two objects, the "car" and the "cdr". The read syntax of a cons cell is an opening parenthesis followed by the read syntax of the car, a dot, the read syntax of the cdr and a closing parenthesis. For example a cons cell with a car of 10 and a cdr of the string `foo' would be written as, (10 . "foo") - Function: cons car cdr This function creates a new cons cell. It will have a car of CAR and a cdr of CDR. (cons 10 "foo") => (10 . "foo") - Function: consp object This function returns true if OBJECT is a cons cell. (consp '(1 . 2)) => t (consp '()) => () (consp (cons 1 2)) => t The strange syntax `'(1 . 2)' is known as "quoting" (*note Quoting::), it tells the evaluator that the object following the quote-mark is a constant, and therefore should not be evaluated. This will be explained in more detail later. In Lisp an "atom" is any object which is not a cons cell (and is, therefore, atomic). - Function: atom object Returns true if OBJECT is an atom (not a cons cell). Given a cons cell there are a number of operations which can be performed on it. - Function: car cons-cell This function returns the object which is the car (first element) of the cons cell CONS-CELL. (car (cons 1 2)) => 1 (car '(1 . 2)) => 1 - Function: cdr cons-cell This function returns the cdr (second element) of the cons cell CONS-CELL. (cdr (cons 1 2)) => 2 (cdr '(1 . 2)) => 2 - Function: rplaca cons-cell new-car This function sets the value of the car (first element) in the cons cell CONS-CELL to NEW-CAR. The value returned is CONS-CELL. (setq x (cons 1 2)) => (1 . 2) (rplaca x 3) => (3 . 2) x => (3 . 2) - Function: rplacd cons-cell new-cdr This function is similar to `rplacd' except that the cdr slot (second element) of CONS-CELL is modified.  File: librep.info, Node: Lists, Next: Vectors, Prev: Cons Cells, Up: Sequences Lists ----- A list is a sequence of zero or more objects, the main difference between lists and vectors is that lists are more dynamic: they can change size, be split, reversed, concatenated, etc... very easily. In Lisp lists are not a primitive type; instead singly-linked lists are formed by chaining cons cells together (*note Cons Cells::). The empty list is represented by the special value `()'. - Function: listp arg This functions returns true when its argument, ARG, is a list (i.e. either a cons cell or `()'). - Function: null arg Returns a true value if ARG is the empty list. * Menu: * List Structure:: How lists are built from cons cells * Building Lists:: Dynamically creating lists * Accessing List Elements:: Getting at the elements which make the list * Modifying Lists:: How to alter the contents of a list * Association Lists:: Lists can represent relations * Infinite Lists:: Circular data structures in Lisp  File: librep.info, Node: List Structure, Next: Building Lists, Up: Lists List Structure .............. Each element in a list is given its own cons cell and stored in the car of that cell. The list is then constructed by having the cdr of a cell point to the cons cell containing the next element (and hence the entire rest of the list). The cdr of the cell containing the last element in the list is `()'. A list of zero elements is represented by `()'. The read syntax of a list is an opening parenthesis, followed by the read syntax of zero or more space-separated objects, followed by a closing parenthesis. Alternatively, lists can be constructed `manually' using dotted-pair notation. All of the following examples result in the same list of five elements: the numbers from zero to four. (0 1 2 3 4) (0 . (1 . (2 . (3 . (4 . ()))))) (0 1 2 . (3 4)) An easy way to visualise lists and how they are constructed is to see each cons cell in the list as a separate "box" with pointers to its car and cdr, +-----+-----+ | o | o----> cdr +--|--+-----+ | --> car Complex box-diagrams can now be drawn to represent lists. For example the following diagram represents the list `(1 2 3 4)'. +-----+-----+ +-----+-----+ +-----+-----+ +-----+-----+ | o | o----> | o | o----> | o | o----> | o | o----> () +--|--+-----+ +--|--+-----+ +--|--+-----+ +--|--+-----+ | | | | --> 1 --> 2 --> 3 --> 4 A more complex example, the list `((1 2) (foo bar))' can be drawn as, +-----+-----+ +-----+-----+ | o | o---------------------------> | o | o----> () +--|--+-----+ +--|--+-----+ | | +-----+-----+ +-----+-----+ +-----+-----+ +-----+-----+ | o | o----> | o | o----> () | o | o----> | o | o----> () +--|--+-----+ +--|--+-----+ +--|--+-----+ +--|--+-----+ | | | | --> 1 --> 2 --> foo --> bar  File: librep.info, Node: Building Lists, Next: Accessing List Elements, Prev: List Structure, Up: Lists Building Lists .............. It has already been described how you can create lists using the Lisp reader; this method does have a drawback though: the list created is effectively static. If you modify the contents of the list and that list was created when a function was defined the list will remain modified for all future invocations of that function. This is not usually a good idea, consider the following function definition, (defun bogus-function (x) "Return a list whose first element is nil and whose second element is X." (let ((result '(nil nil))) ;Static list which is filled in each time (rplaca (cdr result) x) ; the function is called result)) This function does in fact do what its documentation claims, but a problem arises when it is called more than once, (setq x (bogus-function 'foo)) => (nil foo) (setq y (bogus-function 'bar)) => (nil bar) ;The first result has been destroyed x => (nil bar) ;See! This example is totally contrived--no one would ever write a function like the one in the example but it does demonstrate the need for a dynamic method of creating lists. - Function: list #!rest elements This function creates a list out of its arguments, if zero arguments are given the empty list, `()', is returned. (list 1 2 3) => (1 2 3) (list (major-version-number) (minor-version-number)) => (3 2) (list) => () - Function: list* arg1 arg2 ... argn-1 argn Creates a new list `(ARG1 ARG2 ... ARGN-1 . ARGN)'. (list* 1 2 '(3 4)) => (1 2 3 4) - Function: make-list length #!optional initial-value This function creates a list LENGTH elements long. If the INITIAL-VALUE argument is given it defines the value of all elements in the list, if it is not defined they are all `()'. (make-list 2) => (() ()) (make-list 3 t) => (t t t) (make-list 0) => () - Function: append #!rest lists This function creates a new list with the elements of each of its arguments (which must be lists). Unlike the function `nconc' this function preserves the structure of all its arguments. (append '(1 2 3) '(4 5)) => (1 2 3 4 5) (append) => () What actually happens is that all arguments but the last are copied, then the last argument is linked on to the end of the list (uncopied). (setq foo '(1 2)) => (1 2) (setq bar '(3 4)) => (3 4) (setq baz (append foo bar)) => (1 2 3 4) (eq (nthcdr 2 baz) bar) => t The following diagram shows the final state of the three variables more clearly, foo--> +-----+-----+ +-----+-----+ | o | o----> | o | | +--|--+-----+ +--|--+-----+ | | o--> 1 o--> 2 bar | | -> baz--> +--|--+-----+ +--|--+-----+ +-----+-----+ +-----+-----+ | o | o----> | o | o----> | o | o----> | o | | +-----+-----+ +-----+-----+ +--|--+-----+ +--|--+-----+ | | --> 3 --> 4 Note how `foo' and the first half of `baz' use the _same_ objects for their elements--copying a list only copies its cons cells, its elements are reused. Also note how the variable `bar' actually references the mid-point of `baz' since the last list in an `append' call is not copied. - Function: remove elt list Return a copy of LIST, with all elements the same as ELT discarded (using the `equal' function to compare). - Function: remq elt list Similar to the `remove' function, except that comparisons are made using `eq'. - Function: reverse list This function returns a new list; it is made from the elements of the list LIST in reverse order. Note that this function does not alter its argument. (reverse '(1 2 3 4)) => (4 3 2 1) As a postscript to this section, the function used as an example at the beginning could now be written as, (defun not-so-bogus-function (x) (list nil x)) Also note that the `cons' function can be used to create lists by hand and to add new elements onto the front of a list. For example: (setq x (list 1 2 3)) => (1 2 3) (setq x (cons 0 x)) => (0 1 2 3)  File: librep.info, Node: Accessing List Elements, Next: Modifying Lists, Prev: Building Lists, Up: Lists Accessing List Elements ....................... The most flexible method of accessing an element in a list is via a combination of the `car' and `cdr' functions. There are other functions which provide an easier way to get at the elements in a flat list. These will usually be faster than a string of `car' and `cdr' operations. - Function: nth count list This function returns the element COUNT elements down the list, therefore to access the first element use a COUNT of zero (or even better the `car' function). If there are too few elements in the list and no element number COUNT can be found `()' is returned. (nth 3 '(0 1 2 3 4 5)) => 3 (nth 0 '(foo bar) => foo - Function: nthcdr count list This function takes the cdr of the list LIST COUNT times, returning the last cdr taken. (nthcdr 3 '(0 1 2 3 4 5)) => (3 4 5) (nthcdr 0 '(foo bar)) => (foo bar) - Function: last list This function returns the last element in the list LIST. If the list has zero elements `()' is returned. (last '(1 2 3)) => 3 (last '()) => () - Function: member object list This function scans through the list LIST until it finds an element which is `equal' to OBJECT. The tail of the list (the cons cell whose car is the matched object) is then returned. If no elements match OBJECT then the empty list `()' is returned. (member 'c '(a b c d e)) => (c d e) (member 20 '(1 2)) => () - Function: memq object list This function is similar to `member' except that comparisons are performed by the `eq' function not `equal'.  File: librep.info, Node: Modifying Lists, Next: Association Lists, Prev: Accessing List Elements, Up: Lists Modifying Lists ............... The `nthcdr' function can be used in conjunction with the `rplaca' function to modify an arbitrary element in a list. For example, (rplaca (nthcdr 2 '(0 1 2 3 4 5)) 'foo) => foo sets the third element of the list `(0 1 2 3 4 5)' to the symbol called `foo'. There are also functions which modify the structure of a whole list. These are called "destructive" operations because they modify the actual structure of a list--no copy is made. This can lead to unpleasant side effects if care is not taken. - Function: nconc #!rest lists This function is the destructive equivalent of the function `append', it modifies its arguments so that it can return a list which is the concatenation of the elements in its arguments lists. Like all the destructive functions this means that the lists given as arguments are modified (specifically, the cdr of their last cons cell is made to point to the next list). This can be seen with the following example (similar to the example in the `append' documentation). (setq foo '(1 2)) => (1 2) (setq bar '(3 4)) => (3 4) (setq baz (nconc foo bar)) => (1 2 3 4) foo => (1 2 3 4) ;`foo' has been altered! (eq (nthcdr 2 baz) bar) => t The following diagram shows the final state of the three variables more clearly, foo--> bar--> baz--> +-----+-----+ +-----+-----+ +-----+-----+ +-----+-----+ | o | o----> | o | o----> | o | o----> | o | | +--|--+-----+ +--|--+-----+ +--|--+-----+ +--|--+-----+ | | | | --> 1 --> 2 --> 3 --> 4 - Function: nreverse list This function rearranges the cons cells constituting the list LIST so that the elements are in the reverse order to what they were. (setq foo '(1 2 3)) => (1 2 3) (nreverse foo) => (3 2 1) foo => (1) ;`foo' wasn't updated when the list ; was altered. - Function: delete object list This function destructively removes all elements of the list LIST which are `equal' to OBJECT then returns the modified list. (delete 1 '(0 1 0 1 0)) => (0 0 0) When this function is used to remove an element from a list which is stored in a variable that variable must be set to the return value of the `delete' function. Otherwise, if the first element of the list has to be deleted (because it is `equal' to OBJECT) the value of the variable will not change. (setq foo '(1 2 3)) => (1 2 3) (delete 1 foo) => (2 3) foo => (1 2 3) (setq foo (delete 1 foo)) => (2 3) - Function: delq object list This function is similar to the `delete' function, the only difference is that the `eq' function is used to compare OBJECT with each of the elements in LIST, instead of the `equal' function which is used by `delete'. - Function: sort list #!optional predicate Destructively sorts (i.e. by modifying cdrs) the list of values LIST, to satisfy the function PREDICATE, returning the sorted list. If PREDICATE is undefined, the `<' function is used, sorting the list into ascending order. PREDICATE is called with two values, it should return true if the first is considered less than the second. (sort '(5 3 7 4)) => (3 4 5 7) The sort is stable, in that elements in the list which are equal will preserve their original positions in relation to each other.  File: librep.info, Node: Association Lists, Next: Infinite Lists, Prev: Modifying Lists, Up: Lists Association Lists ................. An "association list" (or "alist") is a list mapping keys to to. Each element of the alist is a cons cell, the car of which is the "key", the cdr the value that it associates to. For example an alist could look like, ((fred . 20) (bill . 30)) this alist has two keys, `fred' and `bill' which both associate to an integer (20 and 30 respectively). It is possible to make the associated values lists, this looks like, ((fred 20 male) (bill 30 male) (sue 25 female)) in this alist the symbol `fred' is associated with the list `(20 male)'. There are a number of functions which let you interrogate an alist with a given key for its association. - Function: assoc key alist This function scans the association list ALIST for the first element whose car is `equal' to KEY, this element is then returned. If no match of KEY is found false is returned. (assoc 'two '((one . 1) (two . 2) (three . 3))) => (two . 2) - Function: assq key alist Similar to the function `assoc' except that the function `eq' is used to compare elements instead of `equal'. It is not usually wise to use `assq' when the keys of the alist may not be symbols--`eq' won't think two objects are equivalent unless they are the _same_ object! (assq "foo" '(("bar" . 1) ("foo" . 2))) => () (assoc "foo" '(("bar" . 1) ("foo" . 2))) => ("foo" . 2) - Function: rassoc association alist This function searches through ALIST until it finds an element whose cdr is `equal' to ASSOCIATION, that element is then returned. false will be returned if no elements match. (rassoc 2 '((one . 1) (two . 2) (three . 3))) => (two . 2) - Function: rassq association alist This function is equivalent to `rassoc' except that it uses `eq' to make comparisons.  File: librep.info, Node: Infinite Lists, Prev: Association Lists, Up: Lists Infinite Lists .............. Sometimes it is useful to be able to create `infinite' lists--that is, lists which appear to have no last element--this can easily be done in Lisp by linking the cdr of the last cons cell in the list structure back to the beginning of the list. ----------------------------------- | | --> +-----+-----+ +-----+-----+ | | o | o----> | o | o----- +--|--+-----+ +--|--+-----+ | | --> 1 --> 2 The diagram above represents the infinite list `(1 2 1 2 1 2 ...)'. Infinite lists have a major drawback though, many of the standard list manipulation functions can not be used on them. These functions work by moving through the list until they reach the end. If the list has _no_ end the function may never terminate and the only option is to send the interpreter an interrupt signal. The only functions which may be used on circular lists are: the cons cell primitives (`cons', `car', `cdr', `rplaca', `rplacd'), `nth' and `nthcdr'. Also note that infinite lists can't be printed. But note the `print-length' and `print-level' variables, see *Note Output Functions::.  File: librep.info, Node: Vectors, Next: Strings, Prev: Lists, Up: Sequences Vectors ------- A vector is a fixed-size sequence of Lisp objects, each element may be accessed in constant time--unlike lists where the time taken to access an element is proportional to the position of the element. The read syntax of a vector is an opening square bracket, followed by zero or more space-separated objects, followed by a closing square bracket. For example, [zero one two three] In general it is best to use vectors when the number of elements to be stored is known and lists when the sequence may grow or shrink. - Function: vectorp object This function returns true if its argument, OBJECT, is a vector. - Function: vector #!rest elements This function creates a new vector containing the arguments given to the function. (vector 1 2 3) => [1 2 3] (vector) => [] - Function: make-vector size #!optional initial-value Returns a new vector, SIZE elements big. If INITIAL-VALUE is defined each element of the new vector is set to INITIAL-VALUE, otherwise they are all `()'. (make-vector 4) => [() () () ()] (make-vector 2 t) => [t t]  File: librep.info, Node: Strings, Next: Array Functions, Prev: Vectors, Up: Sequences Strings ------- A string is a vector of characters (*note Characters::), they are generally used for storing and manipulating pieces of text. `librep' puts no restrictions on the values which may be stored in a string--specifically, the null character (`^@') may be stored with no problems. The read syntax of a string is a double quote character, followed by the contents of the string, the object is terminated by a second double quote character. For example, `"abc"' is the read syntax of the string `abc'. Any backslash characters in the string's read syntax introduce an escape sequence; one or more of the following characters are treated specially to produce the next _actual_ character in the string. The following escape sequences are supported (all are shown without their leading backslash `\' character). `n' A newline character. `r' A carriage return character. `f' A form feed character. `t' A TAB character. `a' A `bell' character (this is Ctrl-g). `\' A backslash character. `^C' The `control' code of the character C. This is calculated by toggling the seventh bit of the _upper-case_ version of C. For example, \^C ;A Ctrl-c character (ASCII value 3) \^@ ;The NUL character (ASCII value 0) `012' The character whose ASCII value is the octal value `012'. After the backslash character the Lisp reader reads up to three octal digits and combines them into one character. `x12' The character whose ASCII value is the hexadecimal value `12', i.e. an `x' character followed by one or two hex digits. - Function: stringp object This function returns true if its argument is a string. - Function: make-string length #!optional initial-character Creates a new string containing LENGTH characters, each character is initialised to INITIAL-CHARACTER (or to spaces if INITIAL-CHARACTER is not defined). (make-string 3) => " " (make-string 2 ?$) => "$$" - Function: concat #!rest args This function concatenates all of its arguments, ARGS, into a single string which is returned. If no arguments are given then the null string (`') results. Each of the ARGS may be a string, a character or a list or vector of characters. Characters are stored in strings modulo 256. (concat "foo" "bar") => "foobar" (concat "a" ?b) => "ab" (concat "foo" [?b ?a ?r]) => "foobar" (concat) => "" - Function: substring string start #!optional end This function creates a new string which is a partial copy of the string STRING. The first character copied is START characters from the beginning of the string. If the END argument is defined it is the index of the character to stop copying at, if it is not defined all characters until the end of the string are copied. (substring "xxyfoozwx" 3 6) => "foo" (substring "xyzfoobar" 3) => "foobar" - Function: string= string1 string2 This function compares the two strings STRING1 and STRING2--if they are made from the same characters in the same order then true is returned. (string= "one" "one") => t (string= "one" "two") => () Note that an alternate way to compare strings (or anything!) is to use the `equal' function. - Function: string-equal string1 string2 Returns true if STRING1 and STRING2 are the same, ignoring differences in character case. - Function: string< string1 string2 This function returns true if STRING1 is `less' than `string2'. This is determined by comparing the two strings a character at a time, the first pair of characters which do not match each other are then compared with a normal `less-than' function. In `librep' the standard `<' function understands strings so `string<' is just a macro calling that function. (string< "abc" "abd") => t (string< "abc" "abb") => () - Function: string-lessp string1 string2 Similar to `string<' but ignores character case in comparisons. See *Note String Functions:: for a few more string manipulating functions, and *Note Regular Expressions:: for a method of pattern matching in strings.  File: librep.info, Node: Array Functions, Next: Sequence Functions, Prev: Strings, Up: Sequences Array Functions --------------- - Function: arrayp object This function returns true if OBJECT is an array. - Function: aref array position Returns the element of the array (vector or string) ARRAY POSITION elements from the first element (i.e. the first element is numbered zero). If no element exists at POSITION in ARRAY, false is returned. (aref [0 1 2 3] 2) => 2 (aref "abcdef" 3) => 100 ;`d' - Function: aset array position value This function sets the element of the array ARRAY with an index of POSITION (counting from zero) to VALUE. An error is signalled if element POSITION does not exist. The result of the function is VALUE. (setq x [0 1 2 3]) => [0 1 2 3] (aset x 2 'foo) => foo x => [0 1 foo 3]  File: librep.info, Node: Sequence Functions, Prev: Array Functions, Up: Sequences Sequence Functions ------------------ - Function: sequencep arg Returns true if ARG is a sequence, i.e. a list or an array. - Function: length sequence This function returns the length (an integer) of the sequence SEQUENCE. (length "abc") => 3 (length '(1 2 3 4)) => 4 (length [x y]) => 2 - Function: copy-sequence sequence Returns a new copy of the sequence SEQUENCE. Where possible (in lists and vectors) only the `structure' of the sequence is newly allocated: the same objects are used for the elements in both sequences. (copy-sequence "xy") => "xy" (setq x '("one" "two")) => ("one" "two") (setq y (copy-sequence x)) => ("one" "two") (eq x y) => () (eq (car x) (car y)) => t - Function: elt sequence position This function returns the element of SEQUENCE POSITION elements from the beginning of the sequence. This function is a combination of the `nth' and `aref' functions. (elt [0 1 2 3] 1) => 1 (elt '(foo bar) 0) => foo  File: librep.info, Node: Symbols, Next: Evaluation, Prev: Sequences, Up: The language Symbols ======= Symbols are objects with a name (almost always a unique name). They are one of the most important data types in Lisp since they are used to provided named variables (*note Variables::) and functions (*note Functions::). - Function: symbolp arg This function returns true when its argument is a symbol. * Menu: * Symbol Syntax:: The read syntax of symbols * Symbol Attributes:: The objects stored in a symbol * Obarrays:: Vectors used to store symbols * Creating Symbols:: Allocating new symbols * Interning:: Putting a symbol into an obarray * Property Lists:: Each symbol has a set of properties * Keyword Symbols:: Self-evaluating keywords  File: librep.info, Node: Symbol Syntax, Next: Symbol Attributes, Up: Symbols Symbol Syntax ------------- The read syntax of a symbol is usually its name; however, if the name contains any meta-characters (whitespace or any from `()[]'";|\') they will have to be entered specially. There are two ways to tell the reader that a meta-character is actually part of the symbol's name: 1. Precede the meta-character by a backslash character (`\'), for example: xy\(z\) ;the symbol whose name is `xy(z)' 2. Enclose part of the name in vertical bars (two `|' characters). All characters after the starting vertical line are copied as-is until the closing vertical line is encountered. For example: xy|(z)| ;the symbol `xy(z)' Here are some example read syntaxes. setq ; `setq' |setq| ; `setq' \s\e\t\q ; `setq' 1 ; the _number_ 1 \1 ; the _symbol_ `1' |!$%zf78&| ; `!$%zf78&' foo|(bar)| ; `foo(bar)' foo\(bar\) ; `foo(bar)'  File: librep.info, Node: Symbol Attributes, Next: Obarrays, Prev: Symbol Syntax, Up: Symbols Symbol Attributes ----------------- All symbols have two basic attributes: print name and property list. Most important is the "print name" of the symbol. This is a string naming the symbol, after it has been defined (when the symbol is first created) it may not be changed. - Function: symbol-name symbol This function returns the print name of the symbol SYMBOL. (symbol-name 'unwind-protect) => "unwind-protect" The symbol's "property list" (or plist) is similar to an alist (*note Association Lists::), though stored differently, and provides a method of storing arbitrary extra values in each symbol. *Note Property Lists::. Although not strictly an attribute of the symbol, symbols also provide a means of associating values with names (i.e. variables). Within a defined context, a symbol may have a "binding", this binding associates the symbol with a memory location within which a value may be stored. When writing Lisp programs, the value of a symbol's current binding is accessed by writing the print name of the symbol. Similarly the binding may be modified by using the `setq' special form. *Note Variables::.  File: librep.info, Node: Obarrays, Next: Creating Symbols, Prev: Symbol Attributes, Up: Symbols Obarrays -------- An "obarray" is the structure used to ensure that no two symbols have the same name and to provide quick access to a symbol given its name. An obarray is a vector, each element of the vector is a chain of symbols whose names share the same hash-code (a "bucket"). These symbols are chained together through links which are invisible to Lisp programs: if you examine an obarray you will see that each bucket looks as though it has at most one symbol stored in it. The normal way to reference a symbol is simply to type its name in the program, when the Lisp reader encounters a name of a symbol it looks in the default obarray for a symbol of that name. If the named symbol doesn't exist it is created and hashed into the obarray--this process is known as "interning" the symbol, for more details see *Note Interning::. - Variable: obarray This variable contains the obarray that the `read' function uses when interning symbols. - Function: make-obarray size This function creates a new obarray with SIZE hash buckets (this should probably be a prime number for the fewest hash collisions). This is the only way of creating an obarray. `make-vector' is _not suitable_. - Function: find-symbol symbol-name #!optional obarray This function scans the specified obarray (OBARRAY or the value of the variable `obarray' if OBARRAY is undefined) for a symbol whose name is the string SYMBOL-NAME. The value returned is the symbol if it can be found or false otherwise. (find-symbol "setq") => setq - Function: apropos regexp #!optional predicate obarray Returns a list of symbols from the obarray OBARRAY (or the default) whose print name matches the regular expression REGEXP (*note Regular Expressions::). If PREDICATE is true, each symbol which matches REGEXP is applied to the function PREDICATE, if the value is true it is considered a match. The PREDICATE argument is useful for restricting matches to a certain type of symbol, for example only commands. (apropos "^yank" 'commandp) => (yank-rectangle yank yank-to-mouse)  File: librep.info, Node: Creating Symbols, Next: Interning, Prev: Obarrays, Up: Symbols Creating Symbols ---------------- It is possible to allocate symbols dynamically, this is normally only necessary when the symbol is to be interned in a non-default obarray or the symbol is a temporary object which should not be interned (for example: labels in a compiler). - Function: make-symbol print-name This function creates and returns a new, uninterned, symbol whose print name is the string PRINT-NAME. Its value cell is void (undefined) and it will have an empty property list. (make-symbol "foo") => foo - Function: gensym This function returns a new, uninterned, symbol that has a unique print name. (gensym) => G0001 (gensym) => G0002  File: librep.info, Node: Interning, Next: Property Lists, Prev: Creating Symbols, Up: Symbols Interning --------- "Interning" a symbol means to store it in an obarray so that it can be found in the future: all variables and named-functions are found through interned symbols. When a symbol is interned a hash function is applied to its print name to determine which bucket in the obarray it should be stored in. Then it is simply pushed onto the front of that bucket's chain of symbols. Normally all interning is done automatically by the Lisp reader. When it encounters the name of a symbol which it can't find in the default obarray (the value of the variable `obarray') it creates a new symbol of that name and interns it. This means that no two symbols can have the same print name, and that the read syntax of a particular symbol always produces the same object (unless the value of `obarray' is altered). (eq 'some-symbol 'some-symbol) => t - Function: intern symbol-name #!optional obarray This function uses `find-symbol' to search the OBARRAY (or the standard obarray) for a symbol called SYMBOL-NAME. If a symbol of that name is found it is returned, otherwise a new symbol of that name is created, interned into the obarray, and returned. (intern "setq") => setq (intern "my-symbol" my-obarray) => my-symbol - Function: intern-symbol symbol #!optional obarray Interns the symbol SYMBOL into the obarray OBARRAY (or the standard one) then returns the symbol. If SYMBOL is currently interned in an obarray an error is signalled. (intern-symbol (make-symbol "foo")) => foo (intern-symbol 'foo) error--> Error: Symbol is already interned, foo - Function: unintern symbol #!optional obarray This function removes the symbol SYMBOL from the obarray OBARRAY then returns the symbol. Beware! this function should be used with _extreme_ caution--once you unintern a symbol there may be no way to recover it. (unintern 'setq) ;This is extremely stupid => setq  File: librep.info, Node: Property Lists, Next: Keyword Symbols, Prev: Interning, Up: Symbols Property Lists -------------- Each symbol has a property list (or "plist"), this is a structure which associates an arbitrary Lisp object with a key (usually a symbol). The keys in a plist may not have any duplications (so that each property is only defined once). The concept of a property list is very similar to an association list (*note Association Lists::) but there are two main differences: 1. Structure; each element of an alist represents one key/association pair. In a plist each pair of elements represents an association: the first is the key, the second the property. For example, where an alist may be, ((one . 1) (two . 2) (three . 3)) a property list would be, (one 1 two 2 three 3) 2. Plists have their own set of functions to modify the list. This is done destructively, altering the property list (since the plist is stored in only one location, the symbol, this is quite safe). - Function: get symbol property This function searches the property list of the symbol SYMBOL for a property `equal' to PROPERTY. If such a property is found it is returned, otherwise false is returned. (get 'if 'lisp-indent) => 2 (get 'set 'lisp-indent) => () - Function: put symbol property new-value `put' sets the value of the property PROPERTY to NEW-VALUE in the property list of the symbol SYMBOL. If there is an existing value for this property (using `equal' to compare keys) it is overwritten. The value returned is NEW-VALUE. (put 'foo 'prop 200) => 200 - Function: symbol-plist symbol Returns the property list of the symbol SYMBOL. (symbol-plist 'if) => (lisp-indent 2) - Function: setplist symbol plist This function sets the property list of the symbol SYMBOL to PLIST. (setplist 'foo '(zombie yes)) => (zombie yes)  File: librep.info, Node: Keyword Symbols, Prev: Property Lists, Up: Symbols Keyword Symbols --------------- Keywords are a special class of symbols. They evaluate to themselves, and have the read syntax `#:SYMBOL', where SYMBOL is anything satisfying the usual symbol syntax. These objects are normally used to mark keyword parameters in function applications (*note Lambda Expressions::). - Function: make-keyword symbol Return the keyword symbol that could be used to mark an argument value for the keyword parameter SYMBOL. (make-keyword 'x) => #:x - Function: keywordp arg Returns true if ARG is a keyword symbol.  File: librep.info, Node: Evaluation, Next: Variables, Prev: Symbols, Up: The language Evaluation ========== So far only the primitive data types have been discussed, and how the Lisp reader converts textual descriptions of these types into Lisp objects. Obviously there has to be a way of actually computing something--it would be difficult to write a useful program otherwise. What sets Lisp apart from other languages is that in Lisp there is no difference between programs and data: a Lisp program is just a sequence of Lisp objects which will be evaluated as a program when required. The subsystem which does this evaluation is called the "Lisp evaluator" and each expression to be evaluated is called a "form". The evaluator (the function `eval') examines the structure of the form that is applied to it and computes the value of that form within the current Lisp environment. A form can be any type of data object; the only types which the evaluator treats specially are symbols (which describe variables) and lists (subroutine applications), anything else is returned as-is (and is called a "self-evaluating form"). - Function: eval form This function computes and returns the value of FORM within the current module and dynamic environment, and a null lexical environment. However, `eval' is rarely explicitly invoked, except in the read-eval-print loop. Lisp provides many other methods of evaluation that are usually much more suitable within a program. - Variable: max-lisp-depth This variable limits the number of nested calls to `eval'. If more than this many nested calls to `eval' exist, an error is signalled. The intention is to detect infinite recursion before hitting the stack size limit (causing a segmentation fault). * Menu: * Symbol Forms:: How variables are accessed * List Forms:: Subroutine calls * Self-Evaluating Forms:: Forms which don't get evaluated * Quoting:: How to prevent evaluation of forms  File: librep.info, Node: Symbol Forms, Next: List Forms, Up: Evaluation Symbol Forms ------------ When the evaluator is applied to a symbol the computed value of the form is the value associated with the symbol in the current environment. Basically this means that to get the value of a variable you simply write its name. For example, rep-version => "1.0" this extract from a Lisp session shows the read syntax of a form to get the value of the variable `rep-version' and the result when this form is evaluated. Since forms are evaluated within the current environment the value of a variable is its most-recent extant binding (with slight differences for lexical and special variables). *Note Variables::. If an evaluated symbol has no current binding, an error is signalled.  File: librep.info, Node: List Forms, Next: Self-Evaluating Forms, Prev: Symbol Forms, Up: Evaluation List Forms ---------- Forms which are lists are used to invoke a subroutine. The first element of the list defines the subroutine to be called; all further elements are arguments to be applied to that subroutine invocation. There are several different types of subroutines available: functions, macros, special forms and autoloads. When the evaluator finds a form which is a list it tries to classify the form into one of these four types. First of all it evaluates the first element of the list; the computed value of this element decides how the rest of the elements in the list are treated. For example, if the first element is a symbol whose value is a function, then that function is called with the other values in the list. * Menu: * Function Call Forms:: `Normal' subroutines * Macro Call Forms:: Source code expansions * Special Forms:: Abnormal control structures * Autoload Forms:: Loading subroutines from files on the fly  File: librep.info, Node: Function Call Forms, Next: Macro Call Forms, Up: List Forms Function Call Forms ................... When the first element of a list form evaluates to a function object (either a primitive subroutine or a closure), all other elements in the list are evaluated sequentially from left-to-right, then these values are applied to the function definition. The result returned by the function is then taken as the value of the whole list form. For example, consider the form `(/ 100 (1+ 4))'. This is a function call to the function stored in the variable `/'. First the `/' form is evaluated, it is a variable containing a data value representing the primitive subroutine for integer division. Then the `100' form is evaluated: it is a number, so self-evaluates to the value `100'. Next the form `(1+ 4)' is evaluated. This is also a function call and computes to a value of `5' which becomes the second argument to the `/' function. Now the `/' function is applied to its evaluated arguments of `100' and `5', and returns the value `20'. This then becomes the value of the form `(/ 100 (1+ 4))'. (/ 100 (1+ 4)) == (/ 100 5) => 20 Or another example, (+ (- 10 (1- 7)) (* (1+ 2) 4) == (+ (- 10 6) (* (1+ 2) 4) == (+ 4 (* (1+ 2) 4) == (+ 4 (* 3 4)) == (+ 4 12) => 16 The system is also capable of eliminating tail calls where possible, allowing tail-recursive function definitions to run with bounded space requirements. A "tail-call" is a function call that occurs immediately before exiting the containing function. Since the containing function need not receive the result of the function call, it is possible to, in effect, exit from the containing function before invoking the called function. Note however, that this is only possible where none of the dynamic features of the language (i.e. bindings to special variables, `unwind-protect', `condition-case', `catch', etc...) are currently active in the containing function. Consider, for example, the following function: (defun print-list (l) (unless (null l) (format standard-output "%s\n" (car l)) (print-list (cdr l)))) the call to `print-list' occurs in the "tail-position" of the function. This means that the call may be made after removing the previous call to `print-list' from the interpreter's stack of active functions. [ XXX currently the interpreter is incapable of eliminating tail calls to subrs, i.e. Lisp functions implemented in C ]  File: librep.info, Node: Macro Call Forms, Next: Special Forms, Prev: Function Call Forms, Up: List Forms Macro Call Forms ................ Macros are source code expansions, the general idea is that a macro is a function which using the unevaluated arguments applied to it, computes another form (the expansion of the macro and its arguments) which is then evaluated to provide the value of the form. Macros are generally used to implement control-flow operations, where not all arguments may be evaluated, or evaluated in an unusual order. For more details see *Note Macros::.  File: librep.info, Node: Special Forms, Next: Autoload Forms, Prev: Macro Call Forms, Up: List Forms Special Forms ............. Special forms are built-in subroutines which the evaluator knows must be handled specially. The main difference between a special form and a function is that the arguments applied to a special form are _not_ automatically evaluated--if necessary the special form will evaluate arguments itself. This will be noted in the documentation of the special form. Special forms are generally used to provide control structures, for example, the primitive conditional constructs are special forms (if all of their arguments, including the forms to be conditionally evaluated, were evaluated automatically this would defeat the object of being conditional!). The special forms supported by `librep' are: `cond', `defvar', `progn', `quote', `setq'. - Function: special-form-p arg Returns true if ARG is a special form. (special-form-p quote) => t  File: librep.info, Node: Autoload Forms, Prev: Special Forms, Up: List Forms Autoload Forms .............. Not all parts of `librep' are needed at once, autoload forms provide a means of marking that a function (or macro) is contained by a specific Lisp library. The first time that the function is accessed the autoload form will be evaluated; this loads the file containing the function, then re-evaluates the original form. By then the autoload form will have been overwritten in the symbol's function slot by the true function (when it was loaded) so the form will execute properly. For more details see *Note Autoloading::.  File: librep.info, Node: Self-Evaluating Forms, Next: Quoting, Prev: List Forms, Up: Evaluation Self-Evaluating Forms --------------------- The computed value of any form which is not a symbol or a list will simply be the form itself and the form is said to be a "self-evaluating form". Usually the only forms to be evaluated in this way will be numbers, strings and vectors (since they are the only other data types which have read syntaxes) but the effect is the same for other types of data. This means that forms you know are self-evaluating do not have to be quoted to be used as constants (like lists and symbols do). "foo" => "foo"  File: librep.info, Node: Quoting, Prev: Self-Evaluating Forms, Up: Evaluation Quoting ------- As the above sections explain some types of Lisp object have special meaning to the Lisp evaluator (namely the symbol and list types) this means that if you want to refer to a symbol or a list in a program you can't because the evaluator will treat the form as either a variable reference or a function call respectively. To get around this Lisp uses an idea called "quoting". The special form `quote' simply returns its argument without evaluating it. For example, (quote my-symbol) => my-symbol the `quote' form prevents the `my-symbol' being treated as a variable--it is effectively `hidden' from the evaluator. Writing `quote' all the time would be a bit time-consuming so there is a shortcut: the Lisp reader treats any form X preceded by a single quote character (`'') as the form `(quote X)'. So the example above would normally be written as, 'my-symbol => my-symbol The general way to prevent evaluation of a form is to simply precede it by a single quote-mark. - Special Form: quote form This special form returns its single argument without evaluating it. This is used to "quote" constant objects to prevent them from being evaluated. For another form of quoting, see *Note Backquoting::.  File: librep.info, Node: Variables, Next: Functions, Prev: Evaluation, Up: The language Variables ========= In Lisp, symbols are used to represent variables. Each symbol contains a "value" slot that is used to contain the value of the symbol when it used as a variable. The normal way to obtain the current value of a variable is simply to evaluate the symbol of the same name (i.e. write the name of the variable in your program). The `symbol-value' function can be used to evaluate variables whose names not known statically. - Function: symbol-value variable This function returns the value of the symbol VARIABLE in the current environment. * Menu: * Local Variables:: Creating temporary variables * Setting Variables:: Altering a variable's value * Scope and Extent:: Technical jargon * Void Variables:: Some variables have no values * Defining Variables:: How to define a variable before using it * Fluid Variables:: Another dynamic bindingd methodb  File: librep.info, Node: Local Variables, Next: Setting Variables, Up: Variables Local Variables --------------- A "local variable" is a variable which has a temporary value. For example, when a function is called the variables which are the names of its arguments are temporarily bound to the values of the arguments passed to the function. When the function call exits its arguments are unbound and the previous definitions of the variables come back into view. A "binding" is a particular instance of a local variable. Even if a variable has more than one binding currently in place, only the most recent is available--there is no way the previous binding can be accessed until the previous binding is removed. One way of visualising variable binding is to think of each variable as a stack. When the variable is bound to, a new value is pushed onto the stack, when it is unbound the top of the stack is popped. Similarly when the stack is empty the value of the variable is void (*note Void Variables::). Assigning a value to the variable (*note Setting Variables::) overwrites the top value on the stack with a new value. When the value of the variable is required it is simply read from the top of the stack. Apart from function applications there are two special forms which perform variable binding (i.e. creating local variables), `let' and `let*'. - Macro: let bindings body-forms... `let' creates new variable bindings as specified by the BINDINGS argument, then evaluates the BODY-FORMS in order. The bindings are then removed, returning all variables to their state before the `let' statement was entered. The value of the statement is the value of the implicit `progn'. The BINDINGS argument is a list of the bindings to perform. Each binding is either a symbol, in which case that variable is bound to `()', or a list whose car is a symbol. The cdr of this list is a list of forms which, when evaluated as a `progn', gives the value to bind to that variable. (setq foo 42) => 42 (let ((foo (+ 1 2)) bar) ;; Body forms (setq foo (1+ foo)) ;This sets the new binding (cons foo bar)) => (4 . ()) foo => 42 ;The original values is back No bindings are made until all new values have been computed. For example: (setq foo 42) => 42 (let ((foo 100) (bar foo)) (cons foo bar)) => (100 . 42) Although `foo' is given a new binding this is not actually done until all the new values have been computed, hence `bar' is bound to the _old_ value of `foo'. - Macro: let* bindings body-forms... This special form is exactly the same as `let' except for one important difference: the new bindings are installed _as they are computed_. You can see the difference by comparing the following example with the last example in the `let' documentation (above), (setq foo 42) => 42 (let* ;Using `let*' this time ((foo 100) (bar foo)) (cons foo bar)) => (100 . 100) By the time the new value of `bar' is computed the new binding of `foo' is already active. - Macro: letrec bindings body-forms... `letrec' is similar to `let' and `let*', with the differerence being that the values of bindings are evaluated with all other bindings in scope. This means that recursive functions may be defined with `letrec'. For example, a local factorial function (from SICP): (letrec ((fact (lambda (n) (if (= n 1) 1 (* n (fact (1- n))))))) (fact 10)) Note also that letrec allows groups of mutually recursive functions to be defined, as in the following example (also from SICP): (defun f (x) (letrec ((evenp (lambda (n) (if (= n 0) t (oddp (1- n))))) (oddp (lambda (n) (if (= n 0) nil (evenp (1- n)))))) ...  File: librep.info, Node: Setting Variables, Next: Scope and Extent, Prev: Local Variables, Up: Variables Setting Variables ----------------- "Setting" a variable means to overwrite its current value (that is, the value of its most recent active binding) with a new one. In the variable-as-stack analogy, this is analogous to overwriting the top of the stack. The old value is irretrievably lost (unlike when a new value is bound to a variable, *note Local Variables::). The `setq' special form is the usual method of altering the value of a variable. - Special Form: setq variable form ... Each VARIABLE is set to the result of evaluating its corresponding FORM. The last value assigned becomes the value of the `setq' form. (setq x 20 y (+ 2 3)) => 5 In the above example the variable `x' is set to `20' and `y' is set to the value of the form `(+ 2 3)' (5). - Function: set variable new-value The value of the variable VARIABLE (a symbol) is set to NEW-VALUE and the NEW-VALUE is returned. This function is used when the VARIABLE is unknown until run-time, and therefore has to be computed from a form. (set 'foo 20) == (setq foo 20) ;`setq' means `set-quoted' => 20 _Note:_ currently the `set' function may be used to set any type of variable (i.e. lexical or special). However this likely to change in the future, such that only special variables will be allowed to be modified using the `set' function. It is strongly advised to avoid using this function on lexical bindings! (Moreover the compiler may generate incorrect code in certain circumstances.)  File: librep.info, Node: Scope and Extent, Next: Void Variables, Prev: Setting Variables, Up: Variables Scope and Extent ---------------- In the `librep' dialect of Lisp by default variables have "lexical scope". This means that bindings are associated with textual regions of programs, and may be accessed by any forms within this associated textual region. Moreover, the bindings are persistent, even when the flow of control is currently outside the associated region. Consider the following example: (let ((counter 0)) (defun count () (setq counter (1+ counter)) counter)) the value of the `counter' variable persists, and is incremented each time the `count' function is called. The `counter' variable is accessible from nowhere but the forms written inside the `let' statement declaring it. (count) => 1 (count) => 2 An alternative method of scoping variables is also available. Any variables declared using the `defvar' special form are said to be "special" variables, they have "indefinite scope" and "dynamic extent", often simplified to "dynamic scope". What this means is that references to these variables may occur anywhere in a program (i.e. bindings established in one function are visible within functions called from the original function) and that references may occur at any point in time between the binding being created and it being unbound. Dynamic scoping is easy to abuse, making programs hard to understand and debug. A quick example of the use of dynamic scope, (defvar *foo-var* nil) (defun foo (x) (let ;; a dynamically-scoped binding ((*foo-var* (* x 20))) (bar x) ... (defun bar (y) ;; Since this function is called from ;; the function `foo' it can refer ;; to `*foo-var*' (setq y (+ y *foo-var*)) ... As shown in the previous example, a common convention is to mark special variables by enclosing their names within asterisks.  File: librep.info, Node: Void Variables, Next: Defining Variables, Prev: Scope and Extent, Up: Variables Void Variables -------------- A variable which has no value is said to be "void", attempting to reference the value of such a symbol will result in an error. It is possible for the most recent binding of a variable to be void even though the inactive bindings may have values. - Function: boundp variable Returns true if the symbol VARIABLE has a value. - Function: makunbound variable This function makes the current binding of the symbol VARIABLE be void, then returns VARIABLE. (setq foo 42) => 42 foo => 42 (boundp 'foo) => t (makunbound 'foo) => foo (boundp 'foo) => () foo error--> Value as variable is void: foo  File: librep.info, Node: Defining Variables, Next: Fluid Variables, Prev: Void Variables, Up: Variables Defining Variables ------------------ The special forms `define', `defvar' and `defconst' allow you to define the global variables that will be used by a program. - Macro: define variable form Defines a lexically scoped global variable called VARIABLE. It will have the result of evaluating FORM assigned to it. Note that the `define' special form may also be used to declare block-structured functions, *Note Definitions::. - Special Form: defvar variable [form [doc-string]] This special form defines a special (i.e. dynamically scoped) variable, the symbol VARIABLE. If the value of VARIABLE is void the FORM is evaluated and its value is stored as the value of VARIABLE (note that only the default value is modified, never a buffer-local value). If no FORM is given the assigned value defaults to false. If the DOC-STRING argument is defined it is a string documenting VARIABLE. This string is then stored as the symbol's `variable-documentation' property and can be accessed by the `describe-variable' function. (defvar *my-variable* '(x y) "This variable is an example showing the usage of the `defvar' special form.") => *my-variable* - Macro: defconst constant form [doc-string] `defconst' defines a global constant, the symbol CONSTANT. Its value is set to the result of evaluating FORM. Note that unlike `defvar' the value of the symbol is _always_ set, even if it already has a value. The DOC-STRING argument, if defined, is the documentation string for the constant. (defconst the-answer 42 "An example constant.") => the-answer  File: librep.info, Node: Fluid Variables, Prev: Defining Variables, Up: Variables Fluid Variables --------------- Special variables have a number of drawbacks, especially when used in conjunction with the module system (*note Modules and Special Variables::). As a consequence of these drawbacks, `rep' provides a second method of implementing dynamically scoped variables, known as "fluid variables", or just "fluids". A fluid is a first class Lisp object that may be passed around like any other Lisp object. Its sole function is to provide a location from which dynamic bindings may be created. Fluids are anonymous objects, they are usually named by being stored in lexically scoped variables. - Function: make-fluid #!optional value Create and return a new fluid, it will have an initial binding of VALUE (or false if VALUE is undefined). - Function: fluid fluid Return the value of the most recently created binding of the fluid variable object FLUID. - Function: fluid-set fluid value Set the value of the most recently created binding of the fluid variable object FLUID to VALUE. - Function: with-fluids fluids values thunk Call the zero parameter function THUNK (and return the value that it returns) with new bindings created for each of the fluid variables specified in the list FLUIDS. For each member of FLUIDS the corresponding member of the VALUES list provides the initial value of the new binding. If the lists FLUIDS and VALUES are not of the same length, an error is signalled. - Macro: let-fluids bindings body ... A convenient wrapper around `with-fluids', similar to the `let' syntax. The list BINDINGS associates the names of lexical variables containing fluid objects, with the values to bind to those fluid objects. Once the bindings have been installed, the BODY ... forms are evaluated, and the bindings removed. The value of the last of the BODY ... forms is returned. Here is an example code fragment using fluid variables and `let-fluids': (define a (make-fluid)) (define b (make-fluid)) (let-fluids ((a 1) (b 2)) (+ (fluid a) (fluid b))) => 3  File: librep.info, Node: Functions, Next: Macros, Prev: Variables, Up: The language Functions ========= A "function" is a Lisp object which, when applied to a sequence of argument values, produces another value--the function's "result". It may also induce side-effects (e.g. changing the environment of the calling function). All Lisp functions return results -- there is nothing like a procedure in Pascal. Note that special forms (*note Special Forms::) and macros (*note Macros::) are _not_ functions since they do not guarantee to evaluate all of their arguments. Functions are the main building-block in Lisp programs, each program is usually a system of interrelated functions. There are two types of function: "primitive functions" are functions written in the C language, these are sometimes called built-in functions, the object containing the C code itself is called a "subr". All other functions are defined in Lisp. - Function: functionp object Returns true if OBJECT is a function (i.e. it can be used as the function argument of `funcall'. (functionp set) => t (functionp setq) => () (functionp (lambda (x) (+ x 2))) => t - Function: subrp arg Returns true is ARG is a primitive subroutine object. - Function: subr-name subr Returns a string naming the primitive subroutine SUBR. * Menu: * Lambda Expressions:: Structure of a function object * Defining Functions:: How to write a function definition * Anonymous Functions:: Or they can be un-named * Predicate Functions:: Functions which return boolean values * Local Functions:: Binding functions temporarily * Calling Functions:: Functions can be called by hand * Mapping Functions:: Map a function to the elements of a list  File: librep.info, Node: Lambda Expressions, Next: Defining Functions, Up: Functions Lambda Expressions ------------------ "Lambda expressions" are used to create functions from other Lisp objects. A lambda expression is a list whose first element is the symbol `lambda'. All functions written in Lisp (as opposed to the primitive functions in C) are defined using lambda expressions. The general format of a lambda expression is: (lambda LAMBDA-LIST [DOC] [INTERACTIVE-DECLARATION] BODY-FORMS... ) Where LAMBDA-LIST is a list defining the formal parameters of the function, DOC is an optional documentation string, INTERACTIVE-DECLARATION is only required by interactive commands (1) and BODY-FORMS is the sequence of forms making up the function body, evaluated using an implicit `progn'. The LAMBDA-LIST is a list, it defines how the values applied to the function are bound to local variables which represent the parameters of the function. At its simplest it is simply a list of symbols, each symbol will have the corresponding argument value bound to it. For example, the lambda list `(x y)' defines two parameters, `x' and `y'. When called with two arguments the first will be bound to the variable `x', the second to `y'. When used in a full lambda expression this looks like: (lambda (x y) (+ x y)) this evaluates to an anonymous function with two parameters, `x' and `y', which when called evaluates to their sum. Note that a lambda expression itself is _not_ a function, it must be associated with a lexical environment, this conjunction is usually called a closure; it is the closure that may be called as a function. However, to confuse matters, a lambda expression _evaluates_ to the closure of itself and the current environment. Consider the following example: (lambda (x) (1+ x)) => # (functionp (lambda (x) (1+ x))) => t (functionp '(lambda (x) (1+ x))) => () There are several "lambda-list keywords" which modify the meaning of symbols in the lambda-list. The syntax of the lambda list is: ([REQUIRED-PARAMETERS...] [#!optional OPTIONAL-PARAMETERS...] [#!key KEYWORD-PARAMETERS...] [#!rest REST-PARAMETER | . REST-PARAMETER]) Each lambda list keyword is a symbol whose name begins `#!', they are interpreted as follows: `#!optional' All variables following this keyword are considered "optional" (all variables before the first keyword are "required": an error will be signalled if a required argument is undefined in a function call). OPTIONAL-PARAMETERS may either be of the form `SYMBOL' or of the form `(SYMBOL DEFAULT)'. If no argument is supplied for this parameter the DEFAULT form is evaluated to give the bound value(2). If no DEFAULT form is given, then the variable is bound to a false value. Note that optional parameters must be specified if a later parameter is also specified. ((lambda (#!optional a b) (list a b))) => (() ()) ((lambda (#!optional a b) (list a b)) 1) => (1 ()) ((lambda (#!optional a b) (list a b)) nil 1) => (() 1) ((lambda (#!optional (a 1)) (list a))) => (1) ((lambda (#!optional (a 1)) (list a)) 2) => (2) `#!key' This object marks that the parameters up to the next lambda list keyword are keyword parameters. The values bound to these parameters when the function is called are determined not by position (as with normal parameters), but by being marked by a preceding keyword symbol. Keyword symbols have the syntax `#:SYMBOL'. As with optional parameters, default values may be supplied through the use of the `(SYMBOL DEFAULT)' syntax. If no default value is given and no keyword argument of the specified kind is available, the variable is bound to a false value. For example, the lambda list `(a #!key b c)' accepts one required argument, and two optional keyword arguments. The variable `a' would be bound to the first supplied argument; the variable `b' would be bound to the argument preceded by the keyword `#:b', or `()' if no such argument exists. (After extracting required and optional arguments, each remaining pair of values is checked for associating a value with each keyword.) ((lambda (a #!key b c) (list a b c)) 1 2 3) => (1 () ()) ((lambda (a #!key b c) (list a b c)) 1 #:b 2 3) => (1 2 ()) ((lambda (a #!key b c) (list a b c)) 1 #:b 2 #:c 3) => (1 2 3) ((lambda (a #!key b c) (list a b c)) 1 #:c 3 #:b 2) => (1 2 3) `#!rest' The `#!rest' keyword allows a variable number of arguments to be applied to a function, all the argument values which have not been bound to argument variables (or used to mark keyword arguments) are made into a list and bound to the variable following the `#!rest' keyword. For example, in (lambda (x #!rest y) ...) the first argument, `x', is required. Any other arguments applied to this function are made into a list and this list is bound to the variable `y'. Variable argument functions may also be defined through the Scheme method of using an improper lambda-list. The previous example is exactly equivalent to: (lambda (x . y) ...) When a function represented by a lambda-list is called the first action is to bind the argument values to the formal parameters. The LAMBDA-LIST and the list of argument values applied to the function are worked through in parallel. Any required arguments which are left undefined when the end of the argument values has been reached causes an error. After the arguments have been processed the BODY-FORMS are evaluated by an implicit progn, the value of which becomes the value of the function call. Finally, all parameters are unbound and control passes back to the caller. ---------- Footnotes ---------- (1) Only used when `librep' is embedded within another application. (2) The DEFAULT form is evaluated in the environment of the closure being called, but without any of the bindings created by the lambda expression.  File: librep.info, Node: Defining Functions, Next: Anonymous Functions, Prev: Lambda Expressions, Up: Functions Defining Functions ------------------ Globally accessible functions are usually defined by the `defun' special form. - Macro: defun name lambda-list body-forms... `defun' initialises the function definition of the symbol NAME to the lambda expression resulting from the concatenation of the symbol `lambda', LAMBDA-LIST and the BODY-FORMS. The BODY-FORMS may contain a documentation string for the function as its first form and an interactive calling specification as its first (if there is no doc-string) or second form if the function may be called interactively by the user (*note Lambda Expressions::). An example function definition taken from the `librep' source code is: (defun load-all (file) "Try to load files called FILE (or FILE.jl, etc) from all directories in the Lisp load path." (mapc (lambda (dir) (let ((full-name (expand-file-name file dir))) (when (or (file-exists-p full-name) (file-exists-p (concat full-name ".jl")) (file-exists-p (concat full-name ".jlc"))) (load full-name nil t)))) load-path))  File: librep.info, Node: Anonymous Functions, Next: Predicate Functions, Prev: Defining Functions, Up: Functions Anonymous Functions ------------------- When supplying functions as arguments to other functions it is often useful to give an actual function _definition_ (i.e. an enclosed lambda expression) instead of the name of a function. In Lisp, unlike most other programming languages, functions have no inherent name. As seen in the last section named-functions are created by storing a function object in a variable, if you want, a function can have many different names: simply store the function in many different variables! So, when you want to pass a function as an argument there is the option of just writing down its definition. This is especially useful with functions like `mapc' and `delete-if'. For example, the following form removes all elements from the LIST which are even and greater than 20. (setq LIST (delete-if (lambda (x) (and (zerop (% x 2)) (> x 20))) LIST)) The above lambda expression combines two predicates applied to its argument. In certain cases it may be necessary to create a non-constant function, for example by using backquoting (*note Backquoting::). In these cases the `make-closure' function may be used to create a function object from a lambda expression. - Function: make-closure arg Return the closure of ARG and the current lexical environment. - Function: closurep arg Returns true if ARG is a closure. - Function: closure-function closure Returns the function object associated with the lexical closure CLOSURE.  File: librep.info, Node: Predicate Functions, Next: Local Functions, Prev: Anonymous Functions, Up: Functions Predicate Functions ------------------- In Lisp, a function which returns a boolean `true' or boolean `false' value is called a "predicate". As is the convention in Lisp a value of `()' means false, anything else means true. The symbols `nil' and `t' are often used to represent constant false and true values (*note nil and t::). Another Lisp convention is that the names of predicate functions should name the quality that the predicate is testing followed by either a `p' or `-p' string. The `p' variant is used when the first string does not contain any hyphens. For example, the predicate to test for the quality "const-variable" (a variable which has a constant value, *note Defining Variables::) is called `const-variable-p'. On the other hand the predicate to test for the quality "cons" (a Cons cell) is called `consp'.  File: librep.info, Node: Local Functions, Next: Calling Functions, Prev: Predicate Functions, Up: Functions Local Functions --------------- The `defun' special form allows globally-accessible functions to be defined. It is often desirable to declare functions local to the current lexical environment. The `let' and `let*' special form that were introduced earlier allow this since named functions are simply functional values stored in variables. For example, (let ((temporary-function (lambda (x) (+ x 42)))) ... (temporary-function 20) ...  File: librep.info, Node: Calling Functions, Next: Mapping Functions, Prev: Local Functions, Up: Functions Calling Functions ----------------- Most of the time function applications are made by the evaluator when it finds a functional value after evaluating the first element of a list form. However two functions are available for manually calling functions. - Function: funcall function #!rest args Applies the argument values ARGS to the function FUNCTION, then returns its result. - Function: apply function #!rest args Similar to `funcall' except that the last of its arguments is a _list_ of arguments which are appended to the other members of ARGS to form the list of argument values to apply to the function FUNCTION. (apply + 1 '(2 3)) => 6 (apply + (make-list 1000000 1)) => 1000000  File: librep.info, Node: Mapping Functions, Prev: Calling Functions, Up: Functions Mapping Functions ----------------- A "mapping function" applies a function to each of a collection of objects. `librep' currently has two mapping functions, `mapcar' and `mapc'. - Function: mapcar function list Each element of LIST is individually applied to the function FUNCTION. The values returned are made into a new list which is returned. The FUNCTION must accept a single argument value. (mapcar 1+ '(1 2 3 4 5)) => (2 3 4 5 6) - Function: mapc function list Similar to `mapcar' except that the values returned when each element is applied to the function FUNCTION are discarded. The value returned is undefined. This function is generally used where the side effects of calling the function are the important thing, not the results. It is often the most efficient way of traversing all items in a list, for example: (mapc (lambda (x) (print x standard-error)) list) The two following functions are also mapping functions of a sort. They are variants of the `delete' function (*note Modifying Lists::) and use predicate functions to classify the elements of the list which are to be deleted. - Function: delete-if predicate list This function is a variant of the `delete' function. Instead of comparing each element of LIST with a specified object, each element of LIST is applied to the predicate function PREDICATE. If it returns true then the element is destructively removed from LIST. (delete-if stringp '(1 "foo" 2 "bar" 3 "baz")) => (1 2 3) - Function: delete-if-not predicate list This function does the inverse of `delete-if'. It applies PREDICATE to each element of LIST, if it returns false then the element is destructively removed from the list. (delete-if-not stringp '(1 "foo" 2 "bar" 3 "baz")) => ("foo" "bar" "baz") The `filter' function is similar to `delete-if-not', except that the original list isn't modified, a new list is created. - Function: filter predicate list Return a new list, consisting of the elements in LIST which the function PREDICATE returns true when applied to. This function is equivalent to: (mapcar nconc (mapcar (lambda (x) (and (PREDICATE x) (list x))) LIST))  File: librep.info, Node: Macros, Next: Definitions, Prev: Functions, Up: The language Macros ====== "Macros" are used to extend the Lisp language. They consist of a function which instead of returning a computed value, transform their unevaluated arguments into a new form that, when evaluated, produces the actual value of the original form. For example, the `when' macro (*note Conditional Structures::) implements a new conditional operation by transforming its arguments into a `cond' statement. That is, (when CONDITION FORM ...) ==> (cond (CONDITION FORM ...)) Since macros do not evaluate their arguments, instead just transforming them, they may be expanded at _compile-time_. The resulting form is then compiled as usual. - Function: macrop arg Returns true if ARG is a macro object. * Menu: * Defining Macros:: Macros are defined like functions * Backquoting:: Creating macros from templates * Macro Expansion:: How macros are used by the evaluator * Compiling Macros:: The compiler expands macros at compile- time.  File: librep.info, Node: Defining Macros, Next: Backquoting, Up: Macros Defining Macros --------------- Macros are defined in the same style as functions, the only difference is the name of the special form used to define them. A macro object is a list whose car is the symbol `macro', its cdr is the function which creates the expansion of the macro when applied to the macro calls unevaluated arguments. - Macro: defmacro name lambda-list body-forms... Defines the macro stored in the function cell of the symbol NAME. LAMBDA-LIST is the lambda-list specifying the arguments to the macro (*note Lambda Expressions::) and BODY-FORMS are the forms evaluated when the macro is expanded. The first of BODY-FORMS may be a documentation string describing the macro's use. Here is a simple macro definition, it is the definition of the `when' macro shown in the previous section. (defmacro when (condition #!rest body) "Evaluates CONDITION, if it's true evaluates the BODY forms." (list 'cond (list* condition body))) When a form of the type `(when C B ...)' is evaluated the macro definition of `when' expands to the form `(cond (C (progn B ...)))' which is then evaluated to perform the `when'-construct. When you define a macro ensure that the forms which produce the expansion have no side effects; otherwise undefined effects will occur when programs using the macro are compiled.  File: librep.info, Node: Backquoting, Next: Macro Expansion, Prev: Defining Macros, Up: Macros Backquoting ----------- As seen in the previous sections, macros are a very powerful mechanism of defining new control structures. However due to the need to create the expansion, i.e. the form that will be actually evaluated, they can often be complex to write and understand. We have already seen that constants may be produced through the use of the quote-mark (*note Quoting::), here another form of quoting is described, where only some of the quoted object is actually constant. This is known as "backquoting", since it is introduced by the backquote character ``', a shortcut for the `backquote' macro. - Macro: backquote arg Constructs a new version of ARG (a list). All parts of LIST are preserved except for expressions introduced by comma (`,') characters, which are evaluated and spliced into the list. For example: `(1 2 ,(+ 1 2)) => (1 2 3) Also, the `,@' prefix will splice the following _list_ into the output list, at the same level: `(1 2 ,@(list 3)) => (1 2 3) Backquoting allows macros expansions to be created from static templates. For example the `when' macro shown in the previous sections can be rewritten as: (defmacro when (condition #!rest body) `(cond (,condition ,@body))) which is easier to read, since it is a lot closer to the actual expansion.  File: librep.info, Node: Macro Expansion, Next: Compiling Macros, Prev: Backquoting, Up: Macros Macro Expansion --------------- When a macro call is detected (*note List Forms::) the function which is the cdr of the macro's definition (*note Defining Macros::) is applied to the macro call's arguments. Unlike in a function call, the arguments are _not evaluated_, the actual forms are the arguments to the macro's expansion function. This is to allow these forms to be rearranged by the macro's expansion function, creating the form that will finally be evaluated. There is a function which performs macro expansion, its main use is to let the Lisp compiler expand macro calls at compile time. - Function: macroexpand form #!optional environment If FORM is a macro call `macroexpand' will expand that call by calling the macro's expansion function (the cdr of the macro definition). If this expansion is another macro call the process is repeated until an expansion is obtained which is not a macro call, this form is then returned. The optional ENVIRONMENT argument is a function to call to do the actual expansion. (defmacro when (condition #!rest body) "Evaluates CONDITION, if it's true evaluates the BODY forms." (list 'if condition (cons 'progn body))) => when (macroexpand '(when x (setq foo bar))) => (cond (x (progn (setq foo bar)))) While a macro is being expanded, the special variable `macro-environment' is bound to value of the ENVIRONMENT parameter in the containing call to `macroexpand'. This allows macros to expand inner macros correctly. - Function: macroexpand-1 form #!optional environment Similar to `macroexpand', but only a single macro expansion is ever performed, i.e. if FORM is a macro call the result of expanding that call will be returned, otherwise FORM is returned. (macroexpand-1 '(when x (setq foo bar))) => (if x (progn (setq foo bar)))  File: librep.info, Node: Compiling Macros, Prev: Macro Expansion, Up: Macros Compiling Macros ---------------- Although it may seem odd that macros return a form to produce a result and not simply the result itself, this is actually their most important feature. It allows the expansion and the evaluation of the expansion to occur at different times. The Lisp compiler makes use of this; when it comes across a macro call in a form it is compiling it uses the `macroexpand' function to produce the expansion of that form. This expansion is then compiled straight into the object code. Obviously this is good for performance (why evaluate the expansion every time it is needed when once will do?). Some rules do need to be observed to make this work properly: * The macro expansion function (i.e. the definition of the macro) should not have any side effects or evaluate its arguments (the value of a symbol at compile-time probably won't be the same as its value at run-time). * Macros which are defined by another file must be loaded so they can be recognised. Use the `require' function, the compiler will evaluate any `require' forms it sees loading any macro definitions used. Note however, that the `librep' compiler does allow macros to be used before they are defined (two passes are made through the source file).  File: librep.info, Node: Definitions, Next: Modules, Prev: Macros, Up: The language Block-Structured Definitions ============================ Previous sections of this document have described several special forms and macros for defining top-level functions and variables. `librep' also provides a higher-level method of creating these definitions, the `define' statement. `define' originates in the Scheme dialect of Lisp, it allows block-structured programs to be defined intuitively. The most basic use of `define' is very similar to `defun', e.g. the two following forms have exactly the same effect: (defun foo (x) (1+ x)) (define (foo x) (1+ x)) But note the different position of the parentheses. This is because `define' may also be used to define (lexical) variables. Hence the following is also equivalent: (define foo (lambda (x) (1+ x))) However this is the most uninteresting aspect of `define'. More interesting is that it allows "internal definitions". Within a `define' form, any inner calls to `define' (that occur in a contiguous block at the start of the body of a `let', `let*', `letrec', `lambda', or `define' form) are also used to create definitions, but definitions that are local to the containing scope. For example: (define (foo x) (define (bar) (* x 42)) (1+ (bar))) This defines a top-level function called `foo'. However it also contains an inner function named `bar', that is only accessible within `foo'. Since `bar' is defined inside `foo', and librep uses lexical scope by default, the variable `x' defined by `foo' may also be accessed by `bar'. - Macro: define name form - Macro: define (name . args) body-forms... Define a global lexical variable called NAME, whose value will be set to FORM. If the first argument to the macro is a list, then a function is defined whose name is NAME and whose formal parameters are specified by ARGS. The body of the function is defined by the BODY-FORMS. The body forms have any macros expanded, and are scanned for internal definitions (at the start of the body of `let', `let*', `lambda' special forms) - Macro: define-macro name form - Macro: define-macro (name . args) body-forms... Similar to `define', except that it creates a macro definition (*note Macros::). - Macro: with-internal-definitions body-forms Recursively expand macros in BODY-FORMS, while scanning out any internal definitions into `letrec' statements.  File: librep.info, Node: Modules, Next: Control Structures, Prev: Definitions, Up: The language Modules ======= When creating large programs from many separate components, it is important to be able to encapsulate these components, such that the interfaces they present to other components are well defined, and the implementations of these interfaces may be modified without affecting any other components. To this end `rep' provides a "module system" for managing the scope of global definitions. This module system was inspired by the Scheme48, Xerox Scheme and Standard ML module systems. Modules are known as "structures" and may be anonymous or named. Each structure specifies and implements an "interface", essentially a list of names listing the definitions within that module that may be accessed by other modules. Each structure is a separate global namespace, with a number of variable bindings. Each closure contains a reference to the structure it was instantiated in, for accessing the bindings of any free variables referenced by that closure. As well as specifying its name and interface, each module also lists the other modules whose bindings it may reference. Structures may either "open" or "access" other structures; when opening a structure all its exported bindings are immediately referenceable from the importing module. Exported bindings from accessed structures are referenced using the `structure-ref' form. * Menu: * Module Interfaces:: * Module Definition:: * Module Loading:: * Modules and Special Variables::  File: librep.info, Node: Module Interfaces, Next: Module Definition, Up: Modules Module Interfaces ----------------- Each module implements an interface--the set of bindings (i.e. functions, macros or variables) that it exports to other modules. Interfaces may either be defined and then referenced by name, written literally, or combined from a number of sources. The syntax of interface definitions is as follows: INTERFACE -> (export ID ...) | NAME | (compound-interface INTERFACE ...) | (structure-interface MODULE-NAME) where each ID is the name of a binding to export, and each NAME is the name of an interface previously defined using `define-interface'. - Macro: define-interface name interface Associate the symbol NAME with the module interface INTERFACE (using one of the forms listed above. Here is an example defining an interface called `foo': (define-interface foo (compound-interface bar (export baz quux))) It includes the interface called `bar' and adds two extra exported symbols: `baz' and `quux'.  File: librep.info, Node: Module Definition, Next: Module Loading, Prev: Module Interfaces, Up: Modules Module Definition ----------------- Two special forms are used to define modules, one for anonymous modules, one for named modules. When storing modules in files, each file often contains a single instance of one of these forms. - Macro: structure interface config body... - Macro: define-structure name interface config body... These special forms each create a new module with interface INTERFACE (using the syntax described in the previous section), and configuration CONFIG. After configuring the module as specified, the sequence of forms BODY... is evaluated; it should include the definitions required by the interface that the module has promised to implement. The CONFIG form is either a list of configuration clauses, or a single configuration clause. Each such clause must be of the following syntax: CLAUSE -> (open NAME ...) | (access NAME ...) Each NAME specifies the name of a module, in the case of `open' clauses, the named module(s) will be loaded such that their exported bindings may be referenced from within the current module with no qualification (i.e. as if they had been defined within the module itself). Alternatively, if an `access' clause was used, the named module(s) will be loaded, but their exported bindings will only be accessible from within the current module using the `structure-ref' form. E.g. if a module `foo' has been accessed and it exports a binding named `bar', then the following form could be used to access its value: (structure-ref foo bar) Since this form is used so often, the reader allows the abbreviation `foo#bar' to be used instead, it is expanded to the form above when read. Note that no whitespace is allowed between the three tokens. Note that to access the standard features of the `rep' language described in this manual, modules need to import the `rep' module. Alternatively, they may import the `scheme' module to load a minimal R4RS Scheme environment. Here is an example module definition, defining a module named `test' that exports two functions `foo' and `bar'. (define-structure test (export foo bar) (open rep) (define (foo x) (* x 42)) (define (bar x y) (+ (foo x) (1+ y)))) It is also possible to export multiple views of a single underlying set of bindings, by using the `define-structures' form to create a number of modules. - Macro: define-structures ((name interface) ...) config body... Create a module for each `(NAME INTERFACE)' pair. The module is called NAME and exports the interface defined by INTERFACE. The CONFIG and BODY... forms are as in `define-structure'. Here is a trivial example: (define-structures ((foo (export foo both)) (bar (export bar both))) (open rep) (define both 1) (define foo 2) (define bar 3)) the underlying environment has three bindings. Each created module exports two of these.  File: librep.info, Node: Module Loading, Next: Modules and Special Variables, Prev: Module Definition, Up: Modules Module Loading -------------- As described above, the common way of loading modules is to use the `open' and `access' clauses of the configuration language. If the modules named by these clauses are not currently loaded into the interpreter, then the system will attempt to load them from the filing system, using the standard `load-path' variable to define the directories to search. To allow modules names to be hierarchical, any dot characters in a module's name are replaced by the operating system's directory separator string (i.e. on unix, all `.' characters are simply replaced by `/' characters). When searching for files to load, the standard filename suffixes are used to differentiate Lisp files from other types of files (*note Load Function::). This file should contain a `define-structure' form (as described in the previous section) as the last top-level form in the file. For backwards compatibility, the `require' function can also be used to import modules. If a module of the same name as the requested feature has already been loaded, then it is imported into the current module. Otherwise if a file is loaded that contains a module definition as its last top-level form, this module is imported into the current module. *Note Features::.  File: librep.info, Node: Modules and Special Variables, Prev: Module Loading, Up: Modules Modules and Special Variables ----------------------------- As described earlier, the `defvar' special form may be used to create variables that are scoped dynamically, known as special variables, see *Note Defining Variables::. Due to their dynamic scope, special variables do not fit well with the lexically scoped module system described here. As a result of this mismatch, special variables are stored in a separate namespace. This means that modules defining special variables must take the necessary steps to avoid the names of these variables clashing with those declared in other modules(1). In fact, it is often advisable to avoid using special variables as much as possible, especially when writing modules of Lisp code. An alternative method of creating dynamically scoped variables is to use fluid variable objects. These use first class Lisp objects to represent anonymous dynamically scoped variables. Since they are just Lisp objects, they may be stored in lexically scoped variables--this gives the benefits of both lexical (i.e. encapsulation) and dynamic scoping. *Note Fluid Variables::. ---------- Footnotes ---------- (1) The usual convention is to prefix the variable name with a unique string derived from the module name.  File: librep.info, Node: Control Structures, Next: Threads, Prev: Modules, Up: The language Control Structures ================== Control structures are special forms or macros that control _which_ forms get evaluated, _when_ they get evaluated and the _number_ of times to evaluate them. This includes conditional structures, loops, etc... The simplest control structures are the sequencing structures; they are used to evaluate a list of forms in left to right order. * Menu: * Sequencing Structures:: Evaluating several forms in sequence * Conditional Structures:: Making decisions based on truth values * Looping Structures:: `while' loops * Non-Local Exits:: Exiting from several levels of evaluation * Continuations:: Capturing the call stack  File: librep.info, Node: Sequencing Structures, Next: Conditional Structures, Up: Control Structures Sequencing Structures --------------------- Each of the special forms in this section simply evaluates its arguments in left-to-right order. The only difference is the result returned. The most widely used sequencing special form is `progn': it evaluates all its argument forms and returns the computed value of the last one. Many other control structures are said to perform an "implicit progn", this means that internally they call `progn' with a list of forms. `progn' in Lisp is nearly analogous to a `begin...end' block in Pascal; it is used in much the same places--to allow you to evaluate a sequence of form where only one form was allowed (for example the "true" clause of an `if' structure). - Special Form: progn forms... All of the FORMS are evaluated sequentially (from left-to-right), the result of the last evaluated FORM is the return value of the special form. If no arguments are given to `progn' it returns false. (progn 'one (+ 1 1) "three") => "three" (progn) => () - Macro: prog1 first forms... This special form evaluates its FIRST form then performs an implicit progn on the rest of its arguments. The result of this structure is the computed value of the FIRST form. (prog1 'one (+ 1 1) "three") => one - Macro: prog2 first second forms... This is similar to `prog1' except that the evaluation of its SECOND form is returned. The FIRST form is evaluated, then its SECOND, then it performs an implicit progn on the remaining arguments. (prog2 'one (+ 1 1) "three") => 2  File: librep.info, Node: Conditional Structures, Next: Looping Structures, Prev: Sequencing Structures, Up: Control Structures Conditional Structures ---------------------- Lisp provides a number of conditional constructs, the most complex of which (`cond') takes a list of conditions, the first of which evaluates to true has its associated list of forms evaluated. Theoretically this is the only conditional special form necessary--all others can be implemented as macros. - Macro: if condition true-form else-forms... The `if' form is the nearest thing in Lisp to the "if-then-else" construct found in most programming languages. First the CONDITION form is evaluated, if it returns true the TRUE-FORM is evaluated and its result returned. Otherwise the result of an implicit progn on the ELSE-FORMS is returned. If there are no ELSE-FORMS false is returned. Note that one of the TRUE-FORM or the ELSE-FORMS is completely ignored--it is not evaluated. (if (special-form-p if) "`if' is a special form" "`if' is not a special form") => "`if' is not a special form" - Macro: when condition true-forms... CONDITION is evaluated, if it is true the result of an implicit progn on the TRUE-FORMS is returned, otherwise false is returned. (when t (message "Pointless") 'foo) => foo - Macro: unless condition else-forms... This special form evaluates CONDITION, if its computed value is true, `()' is returned. Otherwise the ELSE-FORMS are evaluated sequentially, the value of the last is returned. - Special Form: cond clause... The `cond' special form is used to choose between an arbitrary number of conditions. Each CLAUSE is a list; the car of which is a CONDITION, the cdr is a list of forms to evaluate (in an implicit `progn') if the CONDITION evaluates to true. This means that each CLAUSE looks something like: (CONDITION BODY-FORMS...) and a whole `cond' form looks like: (cond (CONDITION-1 BODY-FORMS-1...) (CONDITION-2 BODY-FORMS-2...) ...) The CONDITION in each CLAUSE is evaluated in sequence (CONDITION-1, then CONDITION-2, ...), the first one which evaluates to a true value has an implicit `progn' performed on its BODY-FORMS. The value of this `progn' is also the value of the `cond' statement. If the true CONDITION has no BODY-FORMS the value returned is the value of the CONDITION. If none of the clauses has a true CONDITION the value of the `cond' statement is false. Often you want a "default" clause which has its BODY-FORMS evaluated when none of the other clauses are true. The way to do this is to add a clause with a CONDITION of `t' and BODY-FORMS of whatever you want the default action to be. (cond ((stringp buffer-list)) ;Clause with no BODY-FORMS ((consp buffer-list) (setq x buffer-list) ;Two BODY-FORMS t) (t ;Default clause (error "`buffer-list' is corrupted!"))) => t - Macro: case key clauses... This special form is similar to `cond', but switches on the result of evaluating a single form KEY, checking for equality with a number of other values, defined by the CLAUSES. If any of these other values is the same as the result of evaluating KEY, then a sequence of forms associated with the value is evaluated. Each element of the CLAUSES list has the format: ((VALUE-1 VALUE-2 ... VALUE-N) FORMS...) Each of the values in the car of the clause is tested for equality with KEY, using the `eql' function. If any test positively, then the associated FORMS are evaluated and the resulting value becomes the result of the special form. Instead of supplying a list of possible values, it is also possible to just specify the symbol `t'. If such a clause is encountered, and no other clauses have matched the value of KEY, then this clause is assumed to match by default. If any of the values in the CLAUSES appear multiply, then the behaviour of the construct is undefined. Here is an example use of `case': (case foo ((bar baz) (print "It was either bar or baz")) ((quux) (print "It was quux")) (t (print "I've no idea what it was..."))) There are also a number of special forms which combine conditions together by the normal logical rules. - Macro: or forms... The first of the FORMS is evaluated, if it is true its value is the value of the `or' form and no more of `forms' are evaluated. Otherwise this step is repeated for the next member of FORMS. If all of the FORMS have been evaluated and none have a true value the `or' form evaluates to false. (or nil 1 nil (beep)) ;`(beep)' won't be evaluated => 1 - Macro: and forms... The first of the FORMS is evaluated. If it is false no more of the FORMS are evaluated and false is the value of the `and' statement. Otherwise the next member of FORMS is evaluated and its value tested. If none of the FORMS are false the computed value of the last member of FORMS is returned from the `and' form. (and 1 2 nil (beep)) ;`(beep)' won't be evaluated => () (and 1 2 3) ;All forms are evaluated => 3 - Function: not object This function inverts the truth value of its argument. If OBJECT is true, false is returned, otherwise true is returned. (not nil) => t (not t) => () (not (not 42)) => t  File: librep.info, Node: Looping Structures, Next: Non-Local Exits, Prev: Conditional Structures, Up: Control Structures Looping Structures ------------------ The `librep' Lisp dialect only has one method of creating looping control structures--recursion. Any looping construct found in an imperative language can be represented as a recursive function. For example the common `while' statement: (while CONDITION BODY...) == (letrec ((loop (lambda () (when CONDITION BODY (loop))))) (loop)) Each successive iteration of the loop is simply another call to the function. Also note that the recursive call to the `(loop)' function occurs in the tail-position of the function. When combined with the system's ability to eliminate tail-calls (*note Function Call Forms::) the above example loop has bounded space requirements. This is important when loops make a large number of iterations. Although tail-recursion is the only primitive method of looping, the language offers a number of looping forms for convenience. - Macro: do vars (test expr...) body... `do' is an iteration construct; VARS specifies a set of variable bindings to be created, how they are initialized and how they are updated on each iteration. TEST specifies the termination condition of the loop, any EXPR... forms are evaluated immediately prior to exiting the `do' construct. The BODY... forms specify the side effecting body of the loop. VARS is a list of variable clauses, each of which has the structure `(VARIABLE INIT STEP)' where VARIABLE is the name of a variable, INIT defines the initial value of its binding, and STEP defines how the next value of the binding is computed. An alternative form is `(VARIABLE INIT)', in this case the value of the binding does not change across loop iterations. Each iteration begins by evaluating TEST, if the result is false, then the BODY... expressions are evaluated, and the variables bound to new locations initialized to the results of evaluating the associated STEP forms. If the result of evaluating TEST is true then the EXPR... forms are evaluated, and the `do' construct returns the value of the last EXPR form evaluated. (do ((vec (make-vector 5)) (i 0 (1+ i))) ((= i 5) vec) (aset vec i i)) => [0 1 2 3 4] The "named-let" variant of the `let' form also provides a convenient looping construct. - Macro: let variable bindings body... This is the same as the `(let BINDINGS BODY...)' form described in *Note Local Variables::, but within the BODY... forms, the symbol VARIABLE is bound to a function whose parameters are the bound variables defined by BINDINGS and whose body is the sequence of forms BODY... This means that the body of the `let' may be repeated by invoking the function VARIABLE with suitable parameters. (let loop ((rest '(1 2 3)) (total 0)) (if (null rest) total (loop (cdr rest) (+ total (car rest))))) => 6 Finally, the imperative `while' form shown at the start of the section is also provided: - Macro: while condition body... The CONDITION form is evaluated. If it is true an implicit progn is performed on the BODY forms and the whole procedure is repeated. This continues until the CONDITION form evaluates to false. The value of every `while' structure that terminates is false.  File: librep.info, Node: Non-Local Exits, Next: Continuations, Prev: Looping Structures, Up: Control Structures Non-Local Exits --------------- A "non-local exit" is a transfer of control from the current point of evaluation to a different point (somewhat similar to the much-maligned `goto' statement in imperative languages). Non-local exits can either be used explicitly (`catch' and `throw') or implicitly (errors). * Menu: * Catch and Throw:: Programmed non-local exits * Function Exits:: Returning values from a function * Cleanup Forms:: Forms which will always be evaluated * Errors:: Signalling that an error occurred  File: librep.info, Node: Catch and Throw, Next: Function Exits, Up: Non-Local Exits Catch and Throw ............... The `catch' and `throw' structures are used to perform explicit transfers of control. First a `catch' form is used to setup a "tag"; this acts like a label for a `goto' statement. To transfer control a `throw' form is then used to transfer to the named tag. The tag is destroyed and the `catch' form exits with the value provided by the `throw'. In a program this looks like, (catch 'TAG ;; Forms which may `throw' back to TAG ... (throw 'TAG VALUE) ;; Control has now passed to the `catch', ;; no more forms in this progn will be evaluated. ...) => VALUE where TAG is the tag to be used (this is normally a symbol) and VALUE is the result of the `catch' form. When a throw actually happens all catches in scope are searched for one with a tag which is `eq' to the tag in the throw. If more than one exists the innermost is selected. Now that the catch has been located the environment is `wound-back' to the catch's position (i.e. local variables are unbound, cleanup forms executed, unused catches removed, etc...) and all Lisp constructs between the current point of control and the catch are immediately exited. For example, (let ((test 'outer)) (cons (catch 'foo (let ((test 'inner)) (throw 'foo test) (setq test 'unreachable))) ;Never reached test)) => (inner . outer) when the throw executes the second binding of `test' is unwound and the first binding comes back into effect. For more details on variable binding see *Note Local Variables::. Note that catch tags are _dynamically_ scoped, the thrower does not have to be within the same lexical scope (this means that you can `throw' through functions). - Macro: catch tag body-forms... This special form defines a catch tag which will be accessible while the BODY-FORMS are evaluated. TAG is evaluated and recorded as the tag for this catch. Next the BODY-FORMS are evaluated as an implicit `progn'. The value of the `catch' form is either the value of the `progn', or, if a `throw' happened, the value specified in the THROW form. Before exiting, the tag installed by this form is removed. - Function: throw tag #!optional catch-value This function transfers the point of control to the catch form with a tag which is `eq' to TAG. The value returned by this catch form is either CATCH-VALUE or false if CATCH-VALUE is undefined. If there is no catch with a tag of TAG an error is signalled and the interpreter returns to the top-level of evaluation. There are a number of pre-defined throw tags: `quit' Terminate the `librep' interpreter, returning the value of the throw (if a number). `exit' Exit the innermost event loop, unless currently in the outermost event loop, when control just passes back to the event loop. `user-interrupt' As if a `SIGINT' or `C-c' signal has been received. Control passes back to the top-level event loop. `term-interrupt' Triggered when a `SIGTERM' or `SIGHUP' signal is received. Tries to clean up any existing state, then terminates the interpreter. Note that it is the event loop that catches these tags. If no event loop is active (i.e. just in read-eval-print on the console mode), any uncaught throws will result in termination.  File: librep.info, Node: Function Exits, Next: Cleanup Forms, Prev: Catch and Throw, Up: Non-Local Exits Function Exits .............. `librep' has no explicit `return' statement, as found in most other languages. Where a value has to returned from a function before the function would normally exit, a `catch'/`throw' pair may be used. For example: (defun foo (x y) (catch 'return (when (= x 2) (throw 'return nil)) ...  File: librep.info, Node: Cleanup Forms, Next: Errors, Prev: Function Exits, Up: Non-Local Exits Cleanup Forms ............. It is sometimes necessary ensure that a certain form is _always_ evaluated, even when a non-local exit would normally bypass that form. The `unwind-protect' special form is used in this case. - Macro: unwind-protect body-form cleanup-forms... The BODY-FORM is evaluated, if it exits normally the CLEANUP-FORMS are evaluated sequentially then the value which the BODY-FORM returned becomes the value of the `unwind-protect' form. If the BODY-FORM exits abnormally though (i.e. a non-local exit happened) the CLEANUP-FORMS are evaluated anyway and the non-local exit continues. One use of this is to ensure that an opened file is always closed, for example, (catch 'foo (unwind-protect (let ((temporary-file (open-file (make-temp-name) 'write))) ;; Use `temporary-file' (write temporary-file "A test\n") ;; Now force a non-local exit (throw 'foo)) ;; This is the CLEANUP-FORM it will _always_ ;; be evaluated, despite the `throw'. (close temporary-file))) => ()  File: librep.info, Node: Errors, Prev: Cleanup Forms, Up: Non-Local Exits Errors ...... Errors are a type of non-local exit; when a form can not be evaluated for some reason an error is normally "signalled". If an error-handler has been installed for that type of error, control is passed to the handler for that error, and evaluation continues. If there is no suitable handler, control is passed back to the innermost input loop and a suitable error message is printed. - Function: signal error-symbol data Signals that an error has happened. ERROR-SYMBOL is a symbol classifying the type of error, it should have a property `error-message' (a string) which is the error message to be printed. DATA is a list of objects which are relevant to the error -- they will be made available to any error-handler or printed with the error message otherwise. (signal 'void-value '(some-symbol)) error--> Value as variable is void: some-symbol - Variable: debug-on-error This variable is consulted by the function `signal'. If its value is either `t' or a list containing the ERROR-SYMBOL to `signal' as one of its elements, the Lisp debugger is entered. When the debugger exits the error is signalled as normal. - Variable: backtrace-on-error Similar to `debug-on-error', but if an error is matched, the current backtrace is printed to the standard error stream, and control continues. When you expect an error to occur and need to be able to regain control afterwards the `condition-case' special form may be used. - Macro: condition-case symbol body-form error-handlers... `condition-case' evaluates the BODY-FORM with the ERROR-HANDLERS in place. If an error occurs and one of the handles matches the error, then it is evaluated with the value of SYMBOL set to the error information. Each of the ERROR-HANDLERS is a list whose car is a symbol defining the type of error which this handler catches. The cdr of the list is a list of forms to be evaluated in a `progn' if the handler is invoked. While the forms of the error handler are being evaluated the variable SYMBOL is bound to the value `(ERROR-SYMBOL . DATA)' (these were the arguments to the `signal' form which caused the error). If SYMBOL is the symbol `nil' (or the empty list `()'), then the error information is not available to the handler. The special value, the symbol `error', in the car of one of the ERROR-HANDLERS will catch _all_ types of errors. (condition-case data (signal 'file-error '("File not found" "/tmp/foo")) (file-error data) (error (setq x z))) ;Default handler => (file-error "File not found" "/tmp/foo")  File: librep.info, Node: Continuations, Prev: Non-Local Exits, Up: Control Structures Continuations ============= Whenever a function is called, there is a control path waiting to receive the result of the function, e.g. often the form following the function invocation. This waiting control path is called the "continuation" of the function, since control will continue down this path when the called function exits. These continuations are usually not paid much thought, but in some cases it may be useful to be able to directly manipulate the continuation of a function. For this purpose rep provides the `call-with-current-continuation' function (often shortened to `call/cc') that is standard in the Scheme dialect of Lisp. - Function: call/cc function FUNCTION is a function with a single parameter; it will be immediately invoked with this parameter bound to an object representing the current continuation (i.e. the control path that would be taken after FUNCTION exits). The continuation object passed to FUNCTION is itself a function accepting a single argument, when called it transfers control to the continuation of FUNCTION, as if FUNCTION had returned the argument applied to the continuation object. - Function: call-with-current-continuation function This is an alias for `call/cc'. In its simplest form, `call/cc' can mimic the `catch' and `throw' procedures (*note Catch and Throw::), for example: (defun foo (bar) (call/cc (lambda (esc) (when (null bar) ;; throws out of the call/cc (esc nil)) ;; do something with bar ... this is roughly equivalent to: (defun foo (bar) (catch 'tag (when (null bar) (throw 'tag nil)) ;; do something with bar ... This is only half the story--the most powerful feature of `call/cc' is that since continuations have dynamic extent (that is, no object is freed until no references to it exist) it is possible to return control to scopes that have already exited. For example, consider the following fragment of a lisp interaction: (prog1 (call/cc (lambda (esc) (setq cont esc))) (message "foo!")) -| foo! => # cont => # (cont 10) -| foo! => 10 The continuation of the `prog1' form is saved into the variable `cont'. When subsequently called with a single argument, it has exactly the same effect as the first time that the second form in the `prog1' construct was evaluated. Implementation Notes -------------------- `call/cc' works by making a copy of the process' entire call stack. For this reason, it is likely to be less efficient than using the control structures described in the previous parts of this section. Of course, it is much more powerful than the other constructs, so this often outweighs the slight inefficiency. Also note that currently no attempt is made to save or restore the dynamic state of the Lisp system, apart from variable bindings (both lexical and special). This means that any `unwind-protect', `condition-case' or `catch' forms that are active when invoking a continuation are all ignored. Another restriction is that invoking a continuation may not cause control to pass across a dynamic root (*note Threads::).  File: librep.info, Node: Threads, Next: Loading, Prev: Control Structures, Up: The language Threads ======= `librep' supports a simple model of multi-threaded programming. Multiple threads of execution may be created, with control preemptively being switched between them. Unless otherwise noted, all definitions described in this section are provided by the `rep.threads' module. * Menu: * Thread Contexts:: * Creating Threads:: * Deleting Threads:: * Manipulating Threads:: * Mutexes:: * Thread Implementation Notes::  File: librep.info, Node: Thread Contexts, Next: Creating Threads, Up: Threads Thread Contexts --------------- Every thread created by rep is a member of a "thread context", this context is defined by the current position in the lisp call stack. At any point in time, only threads which are members of the current context may be executing. - Function: call-with-dynamic-root thunk Call the function of zero-parameters THUNK in a new thread context. The new context will contain a single thread, that executing THUNK. The call to `call-with-dynamic-root' will only return once all threads in the newly created context have been deleted, or a non-local exit causes control to leave forcibly.  File: librep.info, Node: Creating Threads, Next: Deleting Threads, Prev: Thread Contexts, Up: Threads Creating Threads ---------------- The `make-thread' function may be used to create threads that execute within the current thread context (dynamic root). Each thread is represented by a lisp object. - Function: threadp arg Return true if lisp object ARG represents a thread of execution in the lisp environment. - Function: make-thread thunk #!optional name Create and return a new thread of execution; it will initially invoke the zero-parameter function THUNK. If the call to THUNK returns the thread is automatically deleted. If NAME is defined, it is a string naming the current thread. - Function: make-suspended-thread #!optional name Similar to `make-thread', except that the newly created thread will be immediately suspended from running. - Function: current-thread Returns the currently executing thread. If no threads have been created yet in the current dynamic root (i.e. there is a single "implicit" thread) then false is returned. - Function: all-threads Returns a newly-created list containing all threads in the current dynamic root. If no threads have been created yet, returns a null list.  File: librep.info, Node: Deleting Threads, Next: Manipulating Threads, Prev: Creating Threads, Up: Threads Deleting Threads ---------------- A thread may be deleted by either returning from the function specified when it was created, or by explicit deletion. Also, the implicit thread created by the `call-with-dynamic-root' function may be deleted by exiting from the function called in the new context. - Function: thread-delete #!optional thread Mark THREAD (or the current thread), as being deleted. It will not be switched to in the future. If the current thread is deleted, control will be passed to the next runnable thread. Deleting the last runnable thread results forces the containing dynamic root to be closed. - Function: thread-deleted-p thread Returns true if THREAD has been deleted.  File: librep.info, Node: Manipulating Threads, Next: Mutexes, Prev: Deleting Threads, Up: Threads Manipulating Threads -------------------- - Function: thread-yield This function may be used to pass control away from the current thread if other threads are waiting to run. There is usually no need to call this function since running threads will be preempted after a period of time. - Function: thread-suspend #!optional thread milliseconds Mark THREAD (or the current thread) as being suspended. It will not be selected until either it has had this status removed, or MILLISECONDS milliseconds time has passed. Suspending the current thread will pass control to the next runnable thread in the same dynamic root. If there are no runnable threads, then the interpreter will sleep until the next thread becomes runnable. - Function: thread-join thread #!optional timeout default-value Suspends the current thread until either THREAD has exited, or TIMEOUT milliseconds have passed. If THREAD exits normally, then the value of the last form it evaluated is returned; otherwise DEFAULT-VALUE is returned. It is an error to call `thread-join' on a THREAD that is not a member of the current dynamic root. - Function: thread-wake thread Remove the suspended state from thread THREAD. It will then be scheduled for execution sometime subsequently, if its dynamic root is active. - Function: thread-suspended-p thread Returns true if THREAD is currently suspended. Thread preemption may be forbidden at times, to allow atomic operations to take place. Each dynamic root has its own "forbid counter". Only when this counter is zero may the current thread be preempted. - Function: thread-forbid Increment the forbid count. - Function: thread-permit Decrement the forbid count. - Macro: without-interrupts #!rest forms Evaluate the list of forms FORMS with thread preemption temporarily disabled.  File: librep.info, Node: Mutexes, Next: Thread Implementation Notes, Prev: Manipulating Threads, Up: Threads Mutual Exclusion Devices ------------------------ "Mutexes" are lisp objects used to coordinate access to data shared across multiple threads (where interleaved access would be bad). These functions are exported by the `rep.threads.mutex' module (*note Modules::). - Function: make-mutex Create and return a mutex object. No thread will own the new mutex. - Function: mutexp arg Return true if ARG is a mutex object. - Function: obtain-mutex mutex Obtain the mutex MUTEX for the current thread. Will suspend the current thread until the mutex is exclusively available. - Function: maybe-obtain-mutex mutex Attempt to obtain mutex MUTEX for the current thread without blocking. Returns true if able to obtain the mutex, false otherwise. - Function: release-mutex mutex Release the mutex object MUTEX (which must have previously been obtained by the current thread). Returns true if the mutex has no new owner.  File: librep.info, Node: Thread Implementation Notes, Prev: Mutexes, Up: Threads Thread Implementation Notes --------------------------- The threads used by `librep' are _software threads_. This means that they are currently implemented by manually switching in and out thread context (i.e. the call stack) as required. There are a number of disadvantages to this method: * blocking I/O blocks _all_ threads, not just the thread doing the I/O, * only a single processor is used, thereby avoiding any true parallelism on multi-processor systems. The main advantage is the ease of implementation, especially when retrofitting threads into the previously single-threaded interpreter.  File: librep.info, Node: Loading, Next: Compiled Lisp, Prev: Threads, Up: The language Loading ======= In Lisp, programs (also called "modules", or "libraries") are stored in files. Each file is a sequence of Lisp forms (known as "top-level forms"). Most of the top-level forms in a program will be definitions (i.e. function, macro or variable definitions) since generally each library is a system of related functions and variables. Before the program can be used it has to be "loaded" into the editor's workspace; this involves reading and evaluating each top-level form in the file, i.e. instantiating all function definitions, or whatever. * Menu: * Load Function:: The function which loads programs * Autoloading:: Functions can be loaded on reference * Features:: Module management functions  File: librep.info, Node: Load Function, Next: Autoloading, Up: Loading Load Function ------------- - Function: load program #!optional no-error no-path no-suffix This function loads the file containing the program called PROGRAM; first the file is located then each top-level form contained by the file is read and evaluated in order. Each directory named by the variable `load-path' is searched until the file containing PROGRAM is found. In each directory three different file names are tried, 1. PROGRAM with `.jlc' appended to it. Files with a `.jlc' suffix are usually compiled Lisp files. *Note Compiled Lisp::. 2. PROGRAM with `.jl' appended, most uncompiled Lisp programs are stored in files with names like this. 3. PROGRAM with no modifications. If none of these gives a result the next directory is searched in the same way, when all directories in `load-path' have been exhausted and the file still has not been found an error is signalled. Next the file is opened for reading and Lisp forms are read from it one at a time, each form is evaluated before the next form is read. When the end of the file is reached the file has been loaded and this function returns true. The optional arguments to this function are used to modify its behaviour, NO-ERROR When this argument is true no error is signalled if the file can not be located. Instead the function returns false. NO-PATH The variable `load-path' is not used, PROGRAM must point to the file from the current working directory. NO-SUFFIX When true no `.jlc' or `.jl' suffixes are applied to the PROGRAM argument when locating the file. If a version of the program whose name ends in `.jlc' is older than a `.jl' version of the same file (i.e. the source code is newer than the compiled version) a warning is displayed and the `.jl' version is used. If no Lisp file can be found matching PROGRAM, then each directory in the variable `dl-load-path' is searched for a `libtool' shared library called `PROGRAM.la' (*note Shared Libraries::). - Variable: load-filename Whilst loading a Lisp library, this variable is bound to the name of the file being loaded. - Variable: load-path A list of strings, each element is the name of a directory which is prefixed to the name of a program when Lisp program files are being searched for. load-path => ("/usr/local/lib/rep/1.0/lisp/" "/usr/local/lib/rep/site-lisp/" "") The element `""' refers to the current directory, note that directory names should have an ending `/' (or whatever) so that when concatenated with the name of the file they make a meaningful filename. - Variable: dl-load-path A list of strings defining all directories to search for shared libraries. - Variable: lisp-lib-directory The name of the directory in which the standard Lisp files are stored. lisp-lib-dir => "/usr/local/lib/rep/1.0/lisp/" - Variable: after-load-alist An association list of elements of the format `(FILE FORMS ...)'. When the library FILE is loaded, all FORMS are executed. However, note that FILE must _exactly_ match the PROGRAM argument to the `load' function. - Function: eval-after-load library form Arrange for FORM to be evaluated immediately after the Lisp library of LIBRARY has been read by the `load' function. Note that LIBRARY must exactly match the PROGRAM argument to `load'.  File: librep.info, Node: Autoloading, Next: Features, Prev: Load Function, Up: Loading Autoloading ----------- Obviously, not all features of the `librep' environment are always used. "Autoloading" allows libraries to only be loaded when they are first required. This speeds up the initialisation process and may save memory. Functions which may be autoloaded have a special form in their symbol's function cell--an "autoload form". This is a special kind of closure. When the function call dispatcher finds one of these forms it loads the program file specified in the form then re-evaluates the function call. The true function definition will then have been loaded and therefore the call may proceed as normal. Autoload stubs may be created through the `autoload' function. - Function: autoload symbol file #!optional is-command Installs an autoload form into the symbol SYMBOL. It marks that when SYMBOL is called as a function the lisp library FILE should be loaded to provided the actual definition of SYMBOL. It is not necessary to call the `autoload' function manually. Simply prefix the definitions of all the functions that may be autoloaded (i.e. the entry points to your module; _not_ all the internal functions.) with the magic comment `;;;###autoload'. Then load the file into the Jade editor and invoke the `add-autoloads' command, creating all the necessary calls to the autoload function in the `autoloads.jl' Lisp file (this file which lives in the Lisp library directory is loaded when the environment is initialised). `Meta-x add-autoloads' Scans the current buffer for any autoload definitions. Functions with the comment `;;;###autoload' preceding them have autoload forms inserted into the `autoloads.jl' file. Simply save this file's buffer and the new autoloads will be used the next time Jade is initialised. It is also possible to mark arbitrary forms for inclusion in the `autoloads.jl' file: put them on a single line which starts with the comment `;;;###autoload' call the command. The unsaved `autoloads.jl' buffer will become the current buffer. ;;;###autoload (defun foo (bar) ;`foo' is to be autoloaded ... ;;;###autoload (setq x y) ;Form to eval on initialisation `Meta-x remove-autoloads' Remove all autoload forms from the `autoloads.jl' file which are marked by the `;;;###autoload' comment in the current buffer. The unsaved `autoloads.jl' buffer will become the current buffer. XXX these editor commands don't really belong here, but they'll do for now...  File: librep.info, Node: Features, Prev: Autoloading, Up: Loading Features -------- "Features" correspond to libraries of Lisp code. Each feature is loaded separately. Each feature has a name, when a certain feature is required its user asks for it to be present (with the `require' function), the feature may then be used as normal. When a feature is loaded one of the top-level forms evaluated is a call to the `provide' function. This names the feature and installs it into the list of present features. - Variable: features A list of the features currently present (that is, loaded) in the current module. Each feature is represented by a symbol. Usually the print name of the symbol (the name of the feature) is the same as the name of the file it was loaded from, minus any `.jl' or `.jlc' suffix. features => (info isearch fill-mode texinfo-mode lisp-mode xc) - Function: featurep feature Returns true if the feature FEATURE has been loaded into the current module. - Function: provide feature Adds FEATURE (a symbol) to the list of loaded features. A call to this function is normally one of the top-level forms in a file. ;;;; maths.jl -- the `maths' library (provide 'maths) ... - Function: require feature #!optional file Show that the caller is planning to use the feature FEATURE (a symbol). This function will check the `features' variable to see if FEATURE is already loaded, if so it will return immediately. If FEATURE is not present it will be loaded. If FILE is given it specifies the first argument to the `load' function, else the print name of the symbol FEATURE is used, with any `.' characters replaced by the operating system's directory separator (*note Module Loading::). ;;;; physics.jl -- the `physics' library (require 'maths) ;Need the `maths' library (provide 'physics) ... When called interactively the symbol FEATURE is prompted for. Features may also be provided by modules, for more details *Note Module Loading::.  File: librep.info, Node: Compiled Lisp, Next: Datums, Prev: Loading, Up: The language Compiled Lisp ============= `librep' contains a Lisp compiler as well as an interpreter; this takes a Lisp form or program and compiles it into a "byte-code" object. This byte-code object is a string of characters representing virtual machine instructions, a vector of constants and some other meta-information. The system also contains a byte-code interpreter; this takes the compiled byte-codes and executes them by simulating the virtual machine. This simulation will have exactly the same effect as interpreting the original form or program. One of the main reasons for compiling programs is to increase their efficiency. Compiled functions are likely to be more efficient than interpreted counterparts in all areas (space and time). For example: user> (define (fib n) (if (<= n 2) 1 (+ (fib (- n 1)) (fib (- n 2))))) user> ,time (fib 30) 832040 Elapsed: 17.05572 seconds user> ,compile user> ,time (fib 30) 832040 Elapsed: 1.479007 seconds --the compiled function is over an order of magnitude faster than the interpreted version. * Menu: * Compilation Functions:: How to compile Lisp programs * Compiler Declarations:: Hinting to the compiler * Compilation Tips:: Getting the most out of the compiler * Disassembly:: Examining compiled functions  File: librep.info, Node: Compilation Functions, Next: Compiler Declarations, Up: Compiled Lisp Compilation Functions --------------------- - Function: compile-form form This function compiles the Lisp form FORM into a byte-code form which is returned. (compile-form '(setq foo bar)) => (run-byte-code "F!" [bar foo] 2) - Command: compile-function function This function replaces the uncompiled body of the function FUNCTION (a symbol) with a compiled version, then returns FUNCTION. - Command: compile-file file-name This function compiles the file called FILE-NAME into a file of compiled Lisp forms whose name is FILE-NAME with `c' appended to it (i.e. if FILE-NAME is `foo.jl' it will be compiled to `foo.jlc'). If an error occurs while the file is being compiled any semi-written file will be deleted. When called interactively this function will ask for the value of FILE-NAME. - Command: compile-directory directory #!optional force exclude Compiles all the Lisp files in the directory called DIRECTORY which either haven't been compiled or whose compiled version is older than the source file (Lisp files are those ending in `.jl'). If the optional argument FORCE is true _all_ Lisp files will be recompiled whatever the status of their compiled version. The EXCLUDE argument may be a list of filenames, these files will _not_ be compiled. When this function is called interactively it prompts for the directory. - Command: compile-module module-name Compiles all uncompiled function definitions in the module named MODULE-NAME (a symbol). When called interactively the module name will be prompted for. - Function: run-byte-code byte-codes constants stack Interprets the string of byte instructions BYTE-CODES with the vector of constants CONSTANTS. This function should _never_ be called by hand. The compiler will produce calls to this function when it compiles a form or a function. There is a second form that byte-code objects can take: a vector whose read syntax includes a preceding `#' character is a "byte-code subr". These objects represent compiled Lisp functions and macros. - Function: bytecodep arg Returns true if ARG is a byte-code subroutine.  File: librep.info, Node: Compiler Declarations, Next: Compilation Tips, Prev: Compilation Functions, Up: Compiled Lisp Compiler Declarations --------------------- It is often useful to be able to give the compiler extra knowledge about the program forms that it is compiling. The language includes special declaration forms that have no effect when interpreted, but are meaningful to the compiler as it traverses the program. - Macro: declare clause... Offer the information contained in the CLAUSE... forms to the compiler, which it may or may not use when compiling the program. Each CLAUSE is a list, the first element of each clause is a symbol defining the type of declaration, the interpretation of any other elements in the clause depends upon the declaration type. The following table lists the syntax of all currently supported declaration types: `(bound VARIABLES...)' This declaration tells the compiler that all symbols VARIABLES have lexical bindings for the extent of the current lexical scope. This is often useful to prevent spurious compiler warnings. `(special VARIABLES...)' This tells the compiler that all symbols VARIABLES have special (dynamic) bindings for the extent of the current lexical scope. (It is important that the compiler is able to distinguish special bindings from lexical bindings, since different instruction sequences must be generated to access the different types of binding.) `(unused VARIABLES...)' Directs the compiler not to warn about bindings for VARIABLES... being unreferenced. `(inline NAMES...)' Tells the compiler that it should consider inlining calls to the functions called NAMES.... Inlining will only occur if these functions are declared in the same module as, and after, the declaration itself. `(in-module MODULE-NAME)' This declaration should occur at the top-level of a program; it tells the compiler that the forms in the program will be evaluated within the context of the module called MODULE-NAME (a symbol). `(language MODULE)' Explicitly specifies the particular language dialect that the current module or file body is written for. Language dialects included with the librep distribution include `rep', `scheme' and `unscheme'. These are also the names of the modules that should be imported to use a particular dialect. By default, the `rep' dialect is assumed for code outside module definitions. For code inside a module definition the list of imported modules is scanned for a known language dialect (i.e. if the module imports `rep', then the rep language dialect is compiled for). `(unsafe-for-call/cc)' Tell the compiler that it may register-allocate variables, even if it can't prove that doing so wouldn't produce incorrect results if `call/cc' causes a function call to return more than once (*note Continuations::). This declaration applies to the entire file that it occurs in. Without this declaration, the compiler will only register-allocate bindings if the following conditions are met: * the binding is not accessed from any inner closures, and, * the binding is never modified after being initialized (actually, the binding may be modified between being intialized and the next function call) this declaration is often useful where `call/cc' isn't used, and there is a lot of side effecting of local variables. Declaration forms always evaluate to false. A second type of declaration is the `eval-when-compile' form, it allows Lisp forms to be evaluated only at compile-time. - Macro: eval-when-compile form This form tells the system that FORM should only be evaluated when the containing code is being compiled. The compiler knows to recognize FORMs of the pattern `(eval-when-compile (require 'FEATURE))' as marking that FEATURE should be imported at compile-time. Any other FORMs are simply evaluated in an unspecified environment. When interpreted, `eval-when-compile' forms alway evaluate to false, when compiled they evaluate to the result of evaluating the FORM at compile-time.  File: librep.info, Node: Compilation Tips, Next: Disassembly, Prev: Compiler Declarations, Up: Compiled Lisp Compilation Tips ---------------- Here are some tips for making compiled code run fast(er): * Instead of using `while' loops to traverse lists, use `mapc' or tail recursion. For example you might code a function to scan a list using iteration through a `while' loop: (defun scan-list (lst elt) "Search the LST for an element similar to ELT. Return it if one is found." (catch 'return (while (consp lst) (when (equal (car lst) elt) (throw 'return elt)) (setq lst (cdr lst))))) As well as obscuring what is actually happening, this will probably be fairly slow to execute. A more elegant solution is to use tail-recursion: (defun scan-list (lst elt) (if (equal (car lst) elt) elt (scan-list (cdr lst) elt))) An alternative idiom is to map an anonymous function over the list using the `mapc' function: (defun scan-list (lst elt) (catch 'return (mapc (lambda (x) (when (equal x elt) (throw 'return elt))) lst) nil)) In fact, the compiler knows that calls to `mapc' with a constant lambda expression can be open-coded, so it will code the list traversal directly using the virtual machine stack. However, in most cases the execution time differences are likely to negligible. * In some cases the functions `member', `memq', `assoc', etc... can be used to search lists. Since these are primitives written in C they will probably execute several times faster than an equivalent Lisp function. So the above `scan-list' example can again be rewritten, this time as: (defun scan-list (lst elt) (car (member elt lst))) * All conditional structures are equivalent when compiled (they are all translated to `cond' statements), so use whichever is the easiest to understand. * A certain amount of constant folding is performed. If a function is known to be free of side effects, and all its arguments are constants, then it is evaluated at compile-time, and the result folded into the program in its place. For example (logor (lsh 1 6) x) ==> (logor 32 x) * Careful use of named constants (*note Defining Variables::) can increase the speed of some programs. For example, in the Lisp compiler itself all the opcode values (small integers) are defined as constants. It must be stressed that in some cases constants may _not_ be suitable; they may drastically increase the size of the compiled program (when the constants are `big' objects, i.e. long lists) or even introduce subtle bugs (since two references to the same constant may not be `eq' whereas two references to the same variable are always `eq'). * Many primitives have corresponding byte-code instructions; these primitives will be quicker to call than those that don't (and incur a normal function call). Currently, the functions which have byte-code instructions (apart from all the special forms) are: `cons', `car', `cdr', `rplaca', `rplacd', `nth', `nthcdr', `aset', `aref', `length', `eval', `+', `*', `/', `%', `mod', `lognot', `not', `logior', `logand', `logxor', `equal', `eq', `=', `/=', `>', `<', `>=', `<=', `1+', `1-', `-', `set', `lsh', `zerop', `null', `atom', `consp', `listp', `numberp', `stringp', `vectorp', `throw', `boundp', `symbolp', `get', `put', `signal', `return', `reverse', `nreverse', `assoc', `assq', `rassoc', `rassq', `last', `mapcar', `mapc', `member', `memq', `delete', `delq', `delete-if', `delete-if-not', `copy-sequence', `sequencep', `functionp', `special-form-p', `subrp', `eql', `max', `min', `filter', `macrop', `bytecodep', `bind-object'. * When a file is being compiled each top-level form it contains is inspected to see if it should be compiled into a byte-code form. Different types of form are processed in different ways: * Function and macro definitions have their body forms compiled into a single byte-code form. The doc-string and interactive declaration are not compiled. * If the form is a list form (*note List Forms::) and the symbol which is the car of the list is one of: `if', `cond', `when', `unless', `let', `let*', `catch', `unwind-protect', `error-protect', `with-buffer', `with-window', `progn', `prog1', `prog2', `while', `and', `or', `case'. then the form is compiled. Otherwise it is just written to the output file in its uncompiled state. If your program contains a lot of top-level forms which you know will not be compiled automatically, consider putting them in a `progn' block to make the compiler coalesce them into one byte-code form.  File: librep.info, Node: Disassembly, Prev: Compilation Tips, Up: Compiled Lisp Disassembly ----------- It is possible to disassemble byte-code forms; originally this was so I could figure out why the compiler wasn't working but if you're curious about how the compiler compiles a form it may be of use to you. Naturally, the output of the disassembler is a listing in the assembly language of the `librep' virtual machine--it won't take a byte-code form and produce the equivalent Lisp code! - Command: disassemble-fun function #!optional stream This function disassembles the compile Lisp function FUNCTION. It writes a listing to the output stream STREAM (normally the value of the `standard-output' variable). When called interactively it will prompt for a function to disassemble. When reading the output of the disassembler bear in mind that `librep' simulates a stack machine for the code to run on. All calculations are performed on the stack, the value left on the stack when the piece of code ends is the value of the byte-code form. Here is a small example. Consider the `fib' function given at the start of this section: (define (fib n) (if (<= n 2) 1 (+ (fib (- n 1)) (fib (- n 2))))) After compilation and disassembly, the following is produced (but without the annotations): Disassembly of #: 21 bytes, 1 constants, and (5,0,1) stack slots 0 required-arg ;requires a single parameter 1 dup 2 slot-set #0 ;store it in register 0 (r0) 3 pushi 2 4 le 5 jn 10 ;unless r0 <= 2, goto 10 8 pushi 1 9 return ;else, return 1 10 refg [0] fib 11 slot-ref #0 12 dec 13 call #1 ;push result of (fib (1- n)) 14 refg [0] fib 15 slot-ref #0 16 pushi 2 17 sub 18 call #1 ;push (fib (- n 2)) 19 add 20 return ;return the sum of the two calls  File: librep.info, Node: Datums, Next: Queues, Prev: Compiled Lisp, Up: The language Datums ====== "Datums" are the mechanism by which `librep' allows Lisp programs to define new data types, such that these types are completely distinct from the built-in data types (i.e. they match none of the standard type predicates). They also provide encapsulation, in that the data objects they provide are completely opaque, unless a pre-defined value is known (which was specified when the object was created, and is typically known only by the object's creator). - Function: make-datum value key Create and return a new datum object. It has the value VALUE associated with it, and has type KEY. - Function: datum-ref arg key If ARG has type KEY, then return the value associated with it. Otherwise, an error is signalled. - Function: datum-set arg key value If ARG has type KEY, then set the value associated with it to be VALUE. Otherwise, an error is signalled. - Function: has-type-p arg key Return true if ARG has type KEY. - Function: define-datum-printer key printer Associate the function PRINTER with all datum objects of type KEY. When any such object is printed, PRINTER is applied to two arguments, the datum and the stream to which it should be printed (*note Output Streams::).  File: librep.info, Node: Queues, Next: Records, Prev: Datums, Up: The language Queues ====== A "queue" is an ordered set of objects, such that objects enter at one end of the queue (the "tail"), and leave from the other end of the queue (the "head"). The acts of entering and leaving a queue are often called "enqueing" and "dequeueing". `librep' provides a straightforward queue implementation, implemented by the `rep.data.queues' module (*note Modules::). - Function: make-queue Create and return a new queue object. The queue will initially be empty. - Function: enqueue q arg Add the object ARG to the tail of the queue Q. - Function: dequeue q Remove the object at the head of the queue Q, and return it. If Q is empty, an error is signalled. - Function: queue-empty-p q Return true if the queue Q is not empty. - Function: queuep arg Return true if the object ARG is a queue. - Function: queue->list q Return a list of objects representing the contents of the queue Q, with objects ordered from head to tail. Modifying the list structure causes undefined effects to the queue itself. - Function: queue-length q Return the number of objects stored in the queue Q. - Function: delete-from-queue q arg Removes any occurrences of the object ARG from the queue Q.  File: librep.info, Node: Records, Next: Hash Tables, Prev: Queues, Up: The language Records ======= `librep' provides a convenient means of defining structured data types, these types are known as "records". Each record is a distinct data type, meaning that there will only be a single type-predicate matching objects of any individual record type. All definitions documented in this section are provided by the `rep.data.records' module (*note Modules::). Record types are defined using the `define-record-type' macro, this in turn defines a number of functions implementing the type. These functions include a constructor, a type predicate, and a user-defined set of field-accessor and -modifier functions. - Macro: define-record-type type (constructor fields...) [predicate] (field accessor [modifier])... This macro creates a new record type storing an opaque object identifying the type in the variable named TYPE. It then defines a function CONSTRUCTOR with parameter list as specified by the FIELDS..., and a predicate function called PREDICATE if PREDICATE is given. The fields of the record are defined by the sequence of `(FIELD ACCESSOR [MODIFIER])' forms, each form describes a single field (named FIELD, which may match one of the constructor arguments). For each field a function ACCESSOR will be defined that when applied to an argument of the record type, returns the value stored in the associated FIELD. If the MODIFIER name is defined a function will be defined of that name, that when applied to a record and an object, stores the object into the associated field of the record. Note that the FIELDS... may include all the standard lambda-list features (*note Lambda Expressions::), including keyword parameters and default values. Here is an example record definition: (define-record-type :pare (kons x y) ; constructor pare? ; predicate (x kar set-kar!) ; fields w/ optional accessors (y kdr)) ;and modifiers the variable `:pare' is bound to the record type. Following this definition, the record type could be used as follows: (define x (kons 1 2)) (pare? x) => t (kar x) => 1 (set-kar! x 42) (kar x) => 42 By default record objects print as the name of their type in angle brackets, e.g. for the above `pare' type, each object would print as the string `#<:pare>'. This may be redefined using the `define-record-discloser' function. - Function: define-record-discloser type discloser Associate the function DISCLOSER with the record type TYPE. When any record of this type is printed, DISCLOSER is applied to the object, it should return the value that will actually be printed. For the above example, the following could be used: (define-record-discloser :pare (lambda (x) `(pare ,(kar x) ,(kdr x)))) (kons 'a 'b) => (pare a b) Constructors for records with large numbers of fields often benefit from using keyword parameters. For example the `kons' record above could be defined as follows (though this would make more sense if it had more than two fields): (define-record-type :pare (kons #!key (kar 1) (kdr 2)) pare? (kar kar set-kar!) (kdr kdr set-kdr!)) (kons #:kar 42) => (pare 42 2) (kons #:kdr 42) => (pare 1 42)  File: librep.info, Node: Hash Tables, Next: Guardians, Prev: Records, Up: The language Hash Tables =========== The `rep.data.tables' module provides a flexible hash table implementation (*note Modules::). Each hash table is represented by a lisp object satisfying the `tablep' predicate: - Function: tablep arg Return true if ARG is a hash table. Hash tables may be created by using the `make-table' and `make-weak-table' functions: - Function: make-table hash-fun compare-fun Create and return a new hash table. When storing and referencing keys it will use the function HASH-FUN to map keys to hash codes (positive fixnums), and the predicate function COMPARE-FUN to compare two keys (should return true if the keys are considered equal). - Function: make-weak-table hash-fun compare-fun Similar to `make-table', except that key-value pairs stored in the table are said to be "weakly keyed". That is, they are only retained in the table as long the key has not been garbage collected. Unlike with tables created by the `make-table' function, the fact that the key is stored in the table is not considered good enough to prevent it being garbage collected. - Function: table-ref table key Return the value stored in hash table TABLE indexed by object KEY. Returns false if no such value exists. - Function: table-bound-p table key Returns true if the hash table TABLE contains a value associated with KEY. - Function: table-set table key value Associate the value VALUE with KEY in hash table TABLE. Returns `value'. - Function: table-unset table key Remove any value stored in TABLE associated with KEY. - Function: table-walk function table Call function FUNCTION for every key-value pair stored in hash table TABLE. For each pair, the function is called with arguments `(KEY VALUE)'. Several hash functions are also provided: - Function: string-hash string Return an integer representing the string STRING. - Function: symbol-hash symbol Call `(string-hash (symbol-name SYMBOL))'. - Function: eq-hash arg Return a hash value representing object ARG. The hash is generated from the _address_ of the object. - Function: equal-hash arg Return a hash value representing object ARG. The hash is generated from the _contents_ of the object.  File: librep.info, Node: Guardians, Next: Streams, Prev: Hash Tables, Up: The language Guardians ========= A "guardian" is a lisp object used to control when other data objects are recycled by the garbage collector (*note Garbage Collection::).(1) The usual behaviour of the collector is to recycle objects as soon as they have no remaining references. Guardians allow the programmer to detect when a specified object would be freed by the garbage collector, and to implement their own allocation policy. This can be useful, for example, with objects that have a high creation-overhead, and thus need to be cached for performance reasons. - Function: make-guardian This function allocates and returns a new guardian. Each guardian has a list of data objects associated with it; some of which may have been proved to have no remaining references to them (except from the guardian system). Calling the guardian object with a single argument, adds that value to the list of objects associated with that guardian. Calling the guardian with no arguments has one of two effects: * If objects are associated with the guardian that have been proved to be inaccessible, then return one of those objects, and remove it from the list of objects associated with the guardian. * If none of the associated objects have been proved to be inaccessible, then return the value false. Note the use of the word "prove" in the above description, objects are only moved into a guardian's inaccessible set by the garbage collector. Here is an example use of the guardian system: ;; create a new guardian object (setq G (make-guardian)) ;; create a lisp object (setq x (cons 'a 'b)) => (a . b) ;; protect the object using the guardian (G x) ;; remove the sole reference to the object (setq x nil) => () ;; invoke the garbage collector, this will ;; prove that the value added to the ;; guardian is no longer accessible (garbage-collect) ;; call the guardian to retrieve the ;; inaccessible value (G) => (a . b) ;; no more inaccessible values available (G) => () ---------- Footnotes ---------- (1) Guardians were first described in a paper by R. Kent Dybvig, Carl Bruggeman, and David Eby: `"Guardians in a Generation-Based Garbage Collector", ACM SIGPLAN Conference on Programming Language Design and Implementation, June 1993.'  File: librep.info, Node: Streams, Next: Hooks, Prev: Guardians, Up: The language Streams ======= A "stream" is a Lisp object which is either a data sink (an "output stream") or a data source (an "input stream"). All streams produce or consume sequences of 8-bit characters. Streams are very flexible, functions using streams for their input and output do not need to know the type of stream being accessed. For example the Lisp reader (the `read' function) takes an input stream as its sole argument, it then reads characters from this stream until it has parsed a whole object. This stream could be a file, a function, or even a string; the `read' function does not need to differentiate. - Function: streamp arg Return true if ARG is a stream. - Function: input-stream-p arg Return true if ARG is an input stream. - Function: output-stream-p arg Return true if ARG is an output stream. * Menu: * Input Streams:: Types of input stream * Output Streams:: Types of output stream * Input Functions:: Functions to read from streams * Output Functions:: How to output to a stream * Formatted Output:: Output by template  File: librep.info, Node: Input Streams, Next: Output Streams, Up: Streams Input Streams ------------- These are the possible types of input stream, for the functions which use them see *Note Input Functions::. `FILE' Characters are read from the file object FILE, for the functions which manipulate file objects see *Note Files::. `FUNCTION' Each time an input character is required the FUNCTION is called with no arguments. It should return the character read (an integer) or false if for some reason no character is available. FUNCTION should also be able to `unread' one character. When this happens the function will be called with one argument--the value of the last character read. The function should arrange it so that the next time it is called it returns this character. A possible implementation could be, (defvar ms-unread-char nil "If true the character which was pushed back.") (defun my-stream (#!optional unread-char) (if unread-char (setq ms-unread-char unread-char) (if ms-unread-char (prog1 ms-unread-char (setq ms-unread-char nil)) ;; Normal case -- read and return a character from somewhere ... `nil' Read from the stream stored in the variable `standard-input'. It is also possible to use a string as an input stream. The string to be read from must be applied to the `make-string-input-stream' function and the result from this function used as the input stream. - Function: make-string-input-stream string #!optional start Returns an input stream which will supply the characters of the string STRING in order starting with the character at position START (or from position zero if this argument is undefined). (read (make-string-input-stream "(1 . 2)")) => (1 . 2) - Variable: standard-input The input stream which is used when no other is specified or is false. Applications that embed `librep', or dynamically loaded extensions, may provide further input stream types.  File: librep.info, Node: Output Streams, Next: Input Functions, Prev: Input Streams, Up: Streams Output Streams -------------- These are the different types of output stream, for the functions which use them see *Note Output Functions::. `FILE' Writes to the file object FILE. *Note Files::. `FUNCTION' The function FUNCTION is called with one argument, either a string or a character. This should be used as the circumstances dictate. If the function returns a number it is the number of characters actually used, otherwise it is assumed that all the characters were successful. `PROCESS' Writes to the standard input of the process object PROCESS. If PROCESS isn't running an error is signalled. *Note Processes::. `t' Appends the character(s) to the end of the status line message. `()' Write to the stream stored in the variable `standard-output'. It is also possible to store the characters sent to an output stream in a string. - Function: make-string-output-stream Returns an output stream. It accumulates the text sent to it for the benefit of the `get-output-stream-string' function. - Function: get-output-stream-string string-output-stream Returns a string consisting of the text sent to the STRING-OUTPUT-STREAM since the last call to GET-OUTPUT-STREAM-STRING (or since this stream was created by `make-string-output-stream'). (setq stream (make-string-output-stream)) => ("" . 0) (prin1 keymap-path stream) => ("(lisp-mode-keymap global-keymap)" . 64) (get-output-stream-string stream) => "(lisp-mode-keymap global-keymap)" - Variable: standard-output This variable contains the output stream which is used when no other is specified (or when the given output stream is false). - Variable: standard-error This variable contains the output stream which is used when an error message is being reported. Applications that embed `librep', or dynamically loaded extensions, may provide further output stream types.  File: librep.info, Node: Input Functions, Next: Output Functions, Prev: Output Streams, Up: Streams Input Functions --------------- - Function: read-char stream Read and return the next character from the input stream STREAM. If the end of the stream is reached false is returned. - Function: read-line stream This function reads one line of text from the input stream STREAM, a string containing the line (including the newline character which terminates the line). If the end of stream is reached before any characters can be read false is returned, if the end of stream is reached but some characters have been read (but not the newline) these characters are made into a string and returned. Note that unlike the Common Lisp function of the same name, the newline character is not removed from the returned string. - Function: read stream This function is the function which encapsulates the Lisp reader (*note The Lisp Reader::). It reads as many characters from the input stream STREAM as required to form the read syntax of a single Lisp object (*note Read Syntax::), this object is then returned. - Function: read-from-string string #!optional start Reads one Lisp object from the string STRING, the first character is read from position START (or position zero). (read-from-string STRING START) == (read (make-string-input-stream STRING START))  File: librep.info, Node: Output Functions, Next: Formatted Output, Prev: Input Functions, Up: Streams Output Functions ---------------- - Function: write stream data #!optional length Writes the specified character(s) to the output stream STREAM. DATA is either the character or the string to be written. If DATA is a string the optional argument LENGTH may specify how many characters are to be written. The value returned is the number of characters successfully written. (write standard-output "Testing 1.. 2.. 3..") -| Testing 1.. 2.. 3.. => 19 - Function: copy-stream input-stream output-stream This function copies all characters which may be read from INPUT-STREAM to OUTPUT-STREAM. The copying process is not stopped until the end of the input stream is read. Returns the number of characters copied. Be warned, if you don't choose the streams carefully you may get a deadlock which only an interrupt signal can break! - Function: print object #!optional stream Outputs a newline character to the output stream STREAM, then writes a textual representation of OBJECT to the stream. If possible, this representation will be the read syntax of OBJECT. OBJECT is returned. (print '(1 2 3)) -| -| (1 2 3) => (1 2 3) - Function: prin1 object #!optional stream Similar to `print' but no initial newline is output. (prin1 '(1 2 3)) -| (1 2 3) => (1 2 3) (prin1 '|(xy((z]|) ;A strange symbol -| \(xy\(\(z\] => \(xy\(\(z\] - Function: prin1-to-string object Returns a string containing the characters that `prin1' would output when it prints OBJECT. (prin1-to-string '(1 2 3)) => "(1 2 3)" - Function: princ object #!optional stream Prints a textual representation of OBJECT to the output stream STREAM. No steps are taken to create output that `read' can parse; in particular, no double-quote characters surround strings. (princ "foo") -| foo => "foo" (princ '|(xy((z]|) -| (xy((z] => \(xy\(\(z\] Several variables may be used to control how objects are printed. - Variable: print-escape This defines which control characters `print' and `prin1' will escape (using backslashes). Possible values are: `()' Only escape double-quote and backslash characters. `newlines' Only escape double-quote, backslash, newline, `TAB', and formfeed characters. `t' Escape double-quote, backslash, and all control characters (anything with a numeric value less than 32, or greater than 126). - Variable: print-length This variable, if true, limits the number of elements printed from lists. - Variable: print-level This variable, if true, limits the recursion depth when printing lists.  File: librep.info, Node: Formatted Output, Prev: Output Functions, Up: Streams Formatted Output ---------------- - Function: format stream template #!rest values Writes to a stream, STREAM, a string constructed from the format string, TEMPLATE, and list of arguments VALUES. If STREAM is false the resulting string will be returned, not written to a stream. TEMPLATE is a template for the output string, any `%' characters introduce a substitution, using the next unused argument. The substitutions have the following syntax, %[INDEX$][FLAGS][FIELD-WIDTH]CONVERSION INDEX is an optional decimal number specifying exactly which of the VALUES this conversion refers to (with the first at position one), and is usually used when translating messages; by default the next value is used. FIELD-WIDTH is a positive decimal integer, defining the size in characters of the substitution output. CONVERSION is a character defining how to convert the corresponding argument value to text. The default options are: `s' Write the printed representation of the value without quoting (as if from the `princ' function). `S' Write the printed representation _with_ quoting enabled (like the `prin1' function). `d' Output the value as a decimal number. `o' Write the value in octal. `x' `X' In hexadecimal. `c' Write the character specified by the value. `%' Print a literal percent character. None of the VALUES are used. FLAGS is a sequence of zero or more of the following characters, `_' Left justify the substitution within the field. `^' Truncate the substitution at the size of the field. `0' Pad the field with zeros instead of spaces. `+' For `d', `x', and `o' conversions, output a leading plus sign if the argument is positive. ` ' (a space) For `d', `x', and `o' conversions, if the result doesn't start with a plus or minus sign, output a leading space. The list of CONVERSIONS can be extended through the `format-hooks-alist' variable; the strings created by these extra conversions are formatted as if by the `s' conversion. Note that the FIELD-WIDTH and all flags currently have no effect on the `S' conversion, (or the `s' conversion when the argument isn't a string). If STREAM isn't false (in which case the created string is returned) the value of STREAM is returned. (format nil "foo %S bar 0x%x" '(x . y) 255) => "foo (x . y) bar 0xff" (format standard-output "The %2$s is %1$s!" "purple" "dog") -| The dog is purple! => # - Variable: format-hooks-alist This variable is an association-list, each element being `(CHAR . FUNCTION)', defining extra conversions for the `format' function. If a conversion `%X' is given, and the alist contains an element whose car is the character X, the the associated function is called with one value, the next argument to be formatted. It should return the string to be inserted.  File: librep.info, Node: Hooks, Next: Files, Prev: Streams, Up: The language Hooks ===== A "hook" allows you to wedge your own pieces of Lisp code into the operation of other functions, enable the extension of that functionality. These pieces of code are evaluated via the hook and the result is available to the hook's caller. One hook has already been encountered, the `format-hooks-alist' variable (*note Formatted Output::). * Menu: * Functions As Hooks:: Some hooks are a single function, * Normal Hooks:: Others may be a list of pieces of code to evaluate.  File: librep.info, Node: Functions As Hooks, Next: Normal Hooks, Up: Hooks Functions As Hooks ------------------ Some hooks only allow a single piece of code to be hooked in. Usually a normally-undefined function is used; to install your hook defined a function with the name of the hook. When the hook is to be evaluated the function is called. Generally the name of the hook's function will end in `-function'. An alternative scheme is to use a variable to store the hook, its value should be the function to call.  File: librep.info, Node: Normal Hooks, Prev: Functions As Hooks, Up: Hooks Normal Hooks ------------ This is the standard type of hook, it is a variable whose value is a list of functions. When the hook is evaluated each of the functions will be called in turn. The names of hooks of this type will normally end in `-hook'. These functions are exported by the `rep.system' module. - Function: add-hook hook function #!optional at-end This function adds a new function FUNCTION to the list of functions installed in the (list) hook HOOK (a symbol). If AT-END is true the new function is added at the end of the hook's list of functions (and therefore will be called last when the hook is evaluated), otherwise the new function is added to the front of the list. text-mode-hook => (#) (add-hook 'text-mode-hook my-function) => (# #) - Function: remove-hook hook function This function removes the function FUNCTION from the list of functions stored in the (list) hook HOOK (a symbol). _All_ instances of FUNCTION are deleted from the hook. There are actually three calling conventions for this type of hook, differing in how many of the functions in the list actually get called. In this simplest form, _all_ functions are called. In an `and' type hook, functions are only invoked while all others have returned true. As soon as the first function in the hook returns false, no others will be called. Finally, an `or' type hook aborts when a function returns a true result. - Function: call-hook hook arg-list #!optional type Call the hook named by the symbol HOOK, passing all functions the arguments in the list ARG-LIST. Note that HOOK may also be the actual list of functions to call. TYPE defines how the return values of each function in the hook are treated. If TYPE is false they are ignored, if TYPE is the symbol `and' the hook aborts after a function returns false, if TYPE is `or' the hook aborts when a function returns true. In all cases the value returned by the last-evaluated function is returned.  File: librep.info, Node: Files, Next: Processes, Prev: Hooks, Up: The language Files ===== `librep' allows you to manipulate files in the operating system's filing system; a special type of Lisp object, a "file object", is used to represent files which have been opened for reading or writing (through the streams mechanism, *note Streams::). Names of files are represented by strings, the syntax of file names is defined by the underlying operating system: `librep' simply treats it as a string. Unless otherwise stated, all functions and variables described in the following sections are exported by the `rep.io.files' module. * Menu: * File Names:: Files are named by a string * File Objects:: Lisp objects representing files * File Information:: Predicates on files * Manipulating Files:: Deleting, renaming and copying files * Manipulating Directories:: Accessing directories * Manipulating Symlinks:: Handling symbolic links * File Handlers:: Extending the file name-space * Remote Files:: Accessing remote files  File: librep.info, Node: File Names, Next: File Objects, Up: Files File Names ---------- A "file name" is a string identifying an individual file (or directory) in the filing system (i.e. the disk). The exact syntax of file names depends on the operating system. There are several functions for manipulating file names. - Function: file-name-absolute-p file-name Returns true when FILE-NAME is not specified relative to the current directory. - Function: file-name-directory file-name This function returns the directory part of the file name string FILE-NAME. This is the substring of FILE-NAME defining the directory containing the file. (file-name-directory "/tmp/foo") => "/tmp/" (file-name-directory "foo") => "" (file-name-directory "foo/bar/") => "foo/bar/" - Function: file-name-nondirectory file-name Returns the substring of the file name FILE-NAME which is _not_ the directory part. (file-name-nondirectory "/tmp/foo") => "foo" (file-name-nondirectory "foo") => "foo" (file-name-nondirectory "foo/bar/") => "" - Function: file-name-as-directory file-name Returns a string through which the item in the file system named by FILE-NAME can be referred to as a directory. (file-name-as-directory "./foo") => "./foo/" (file-name-as-directory "./foo/") => "./foo/" - Function: directory-file-name directory-name Returns a string through which the directory named by DIRECTORY-NAME can be referred to as a file. (directory-file-name "./foo/") => "./foo" (directory-file-name "./foo") => "./foo" - Function: expand-file-name file-name #!optional base-dir Expands FILE-NAME assuming that it specifies a file relative to BASE-DIR. If BASE-DIR is undefined it is taken as the current value of the `default-directory' variable. While expanding the file name, any obvious simplifications will be performed (e.g. on Unix the removal of "." and ".." where possible). Note that the returned file name will only be absolute if one of the following conditions is met: 1. BASE-DIR (or `default-directory') is absolute, 2. FILE-NAME is already absolute. (expand-file-name "foo" "./bar") => "bar/foo" Note for file handler implementors: when a handler is called for the `expand-file-name' operation, it will only ever receive one argument, the already expanded file name. The only action that may be need to be taken is to simplify the file name (e.g. removing `.' and `..' entries or whatever). - Function: canonical-file-name file-name This function returns the canonical name of the file referred to by the string FILE-NAME. The canonical name of a file is defined such that two files can be compared simply by comparing their canonical names; if the names match, they refer to the same file. (Note that the opposite isn't always true, if two canonical names don't match the files could still be the same, for example via hard links. On most operating systems, symbolic links will be expanded where possible. (canonical-file-name "foo") => "/home/john/src/librep/man/foo" - Function: local-file-name file-name `librep' supports extensible file handling (*note File Handlers::), so file names may refer to files not residing in the system's local file structure, and thus which are unavailable to other programs. This function returns either the absolute name of the file FILE-NAME, if it is found in the local system, or false, if the file does not. (local-file-name "foo") => "/home/john/src/librep/man/foo" (local-file-name "/john@tango:foo") => () - Function: make-temp-name This function returns the name of a file which, when created, may be used for temporary storage. Each time this function is called a unique name is computed. (make-temp-name) => "/tmp/00088aaa" (make-temp-name) => "/tmp/00088baa" - Variable: default-directory This variable names the current working directory. All relative file names are interpreted starting from this location in the file system.  File: librep.info, Node: File Objects, Next: File Information, Prev: File Names, Up: Files File Objects ------------ A file object is a Lisp object which represents an open file in the filing system. Any file object may be used as a stream (either input or output) to access the contents of the file (*note Streams::). - Function: filep object This function returns true when its argument is a file object. * Menu: * Creating File Objects:: Opening files * Destroying File Objects:: Closing files * Functions on File Objects:: Functions operating on file objects  File: librep.info, Node: Creating File Objects, Next: Destroying File Objects, Up: File Objects Creating File Objects ..................... - Function: open-file file-name mode This function opens the file called FILE-NAME (*note File Names::) and returns the new file object. The MODE argument is a symbol defining the access modes used to open the file with, the options are: `read' Open an existing file for reading only. `write' Open the file for writing only, if the file exists it is truncated to zero length. Otherwise a new file is created. `append' Open the file for appending to, i.e. writing to the end of the file. If the file doesn't exist it is created. The three standard I/O streams are also available as file handles. - Function: stdin-file Return a file object representing the interpreters standard input. - Function: stdout-file Return a file object representing the interpreters standard output. - Function: stderr-file Return a file object representing the interpreters standard error. Attempting to close any of these files will result in the associated stream being connected to `/dev/null'.  File: librep.info, Node: Destroying File Objects, Next: Functions on File Objects, Prev: Creating File Objects, Up: File Objects Destroying File Objects ....................... The easiest way to close a file is simply to eliminate all references to it, subsequently the garbage collector will close it for you. It is better to close files explicitly though since only a limited number of files may be opened concurrently. - Function: close-file file-object This function closes the file pointed to by the file object FILE-OBJECT. Subsequently, any stream accesses FILE-OBJECT are illegal and will signal an error.  File: librep.info, Node: Functions on File Objects, Prev: Destroying File Objects, Up: File Objects Functions on File Objects ......................... - Function: seek-file file #!optional offset where When called as `(seek-file FILE)', returns the distance in bytes from the start of the file that the next character would be read from. When called as `(seek-file FILE OFFSET [WHERE])' alters the position from which the next byte will be read. WHERE can be one of the values: `()' OFFSET bytes after the current position. `start' OFFSET bytes after the beginning of the file. `end' OFFSET bytes before the end of the file. Note that not all files may be seekable; if `(seek-file FILE)' returns false, indicating that the current position is unknown, any attempts to set the current position will also fail. - Function: flush-file file This function flushes any buffered output to the file object FILE to disk. - Function: file-binding file Returns the name of the file which the file object FILE is currently bound to. Returns false if the file is currently unbound (i.e. `close-file' was called on it). The next three functions are used when non-local files are being accessed. See *Note File Handlers:: for more details. - Function: file-bound-stream file If the file object FILE doesn't refer to a file in the local filing system, return the stream that it is bound to (allowing the file's contents to be accessed), this may or may not be another file object. - Function: file-handler-data file Return the file-handler-specific data associated with the file object FILE. - Function: set-file-handler-data file data Set the handler-specific data of file object FILE to DATA. This should only be done by the handler owning the file. It's also possible to register a callback function to be invoked when input is available on a file, - Function: set-input-handler local-file function Arrange for FUNCTION to be called whenever pending input is available on LOCAL-FILE, a file object bound to a file in the local file space. Note that this makes LOCAL-FILE subsequently do non-blocking input. This function is normally only useful when LOCAL-FILE represents a pipe or socket.  File: librep.info, Node: File Information, Next: Manipulating Files, Prev: File Objects, Up: Files File Information ---------------- A number of functions exist which when given the name of a file return one of the attributes relating to that file. - Function: file-exists-p file-name Returns true when a file FILE-NAME exists. - Function: file-regular-p file-name Returns true when the file FILE-NAME is a `normal' file. This means that it isn't a directory, device, symbolic link or whatever. - Function: file-directory-p file-name Returns true when the file FILE-NAME is a directory. - Function: file-symlink-p file-name Returns true when the file FILE-NAME is a symbolic link. - Function: file-readable-p file-name Returns true when the file FILE-NAME is readable. - Function: file-writable-p file-name Returns true when the file FILE-NAME is writable. - Function: file-owner-p file-name Returns true when the ownership of the file FILE-NAME is the same as that of any files written by the editor. - Function: file-size file-name Returns the number of bytes stored in the file named FILE-NAME. - Function: file-nlinks file-name Returns the number of hard links pointing to the file FILE-NAME. If FILE-NAME has only one name the number will be one. - Function: file-modes file-name This function returns the access permissions of the file FILE-NAME. This will be an integer whose format is undefined; it differs from operating system to operating system. - Function: file-modes-as-string file-name Returns a ten-character string describing the attibutes of the file called FILE-NAME (file-modes-as-string ".") => "drwxr-sr-x" - Function: set-file-modes file-name modes This function sets the access permissions of the file FILE-NAME to the integer MODES (as returned by the `file-modes' function). - Function: file-modtime file-name Returns the system time at the last modification to the file FILE-NAME, this will be in the usual timestamp format, *Note Timestamps::. - Function: file-newer-than-file-p file-name1 file-name2 This function returns true if the file FILE-NAME1 was modified more recently than the file FILE-NAME2 was.  File: librep.info, Node: Manipulating Files, Next: Manipulating Directories, Prev: File Information, Up: Files Manipulating Files ------------------ - Command: delete-file file-name This function deletes the file called FILE-NAME. When called interactively FILE-NAME is prompted for. - Command: rename-file file-name new-name This function attempts to change the name of the file NEW-NAME to NEW-NAME. This won't work from one file system to another or if a file called NEW-NAME already exists, in these cases an error is signalled. This prompts for its arguments when called interactively. - Command: copy-file file-name destination-name Creates a new copy of the file FILE-NAME with the name DESTINATION-NAME. The access modes of the new file will be the same as those of the original file. The arguments are prompted for when this function is called interactively.  File: librep.info, Node: Manipulating Directories, Next: Manipulating Symlinks, Prev: Manipulating Files, Up: Files Manipulating Directories ------------------------ - Command: make-directory directory-name Create a new directory called DIRECTORY-NAME. - Command: delete-directory directory-name Delete the directory called DIRECTORY-NAME. This only succeeds if the directory in question is empty, otherwise an error is signalled. - Function: directory-files directory-name Returns a list of the names of all items in the directory whose name is DIRECTORY-NAME. The names in the list will be relative to the directory DIRECTORY-NAME. (directory-files "/tmp/foo" => ("bar" "subdir" "xyz" "." "..")  File: librep.info, Node: Manipulating Symlinks, Next: File Handlers, Prev: Manipulating Directories, Up: Files Manipulating Symbolic Links --------------------------- - Function: make-symlink name contents Create a symbolic link called NAME, containing the string CONTENTS. - Function: read-symlink name Return the string that is the contents of the symbolic link called NAME. Signals an error if no such link exists.  File: librep.info, Node: File Handlers, Next: Remote Files, Prev: Manipulating Symlinks, Up: Files File Handlers ------------- As noted earlier, `librep' supports virtual files; that is it allows file names to be accessed that don't reside on the local filing system, or aren't normally valid as file names. This is achieved through the use of "file handlers", Lisp functions that have signalled that they should be used to redirect all accesses to files whose names match a particular regular expression (*note Regular Expressions::). For example, there is a convention under Unix that a user's home directory can be accessed via the file name `~', even though there is no such support from the operating system itself. So a file handler can be (and has been) written that recognises all file names starting with a tilde, translating them to the actual file in the file system. - Variable: file-handler-alist This variable contains a list of file handler declarations, each one of the form `(REGEXP . FUNCTION)'. Whenever a file operation is performed on a file whose name matches REGEXP, FUNCTION is invoked to perform the action. The function is called as `(FUNCTION OPERATION ARGS...)', where OPERATION and ARGS are from the original call. For example if the `file-handler-alist' contains the entry `("^~" . tilde-file-handler)', then all file operations on files starting with a tilde are redirected to the `tilde-file-handler' function. Thus if a form `(file-exists-p "~/foo")' is executed, it would result in a call to `tilde-file-handler' as `(tilde-file-handler 'file-exists-p "~/foo")'. The list of operations that may be redirected to a file handler is: `file-name-absolute-p', `expand-file-name', `local-file-name', `canonical-file-name', `file-name-nondirectory', `file-name-directory', `file-name-as-directory', `directory-file-name', `open-file', `close-file', `flush-file', `seek-file', `write-buffer-contents', `read-file-contents', `insert-file-contents', `delete-file', `rename-file', `copy-file', `copy-file-to-local-fs', `copy-file-from-local-fs', `make-directory', `delete-directory', `file-exists-p', `file-regular-p', `file-readable-p', `file-writable-p', `file-directory-p', `file-symlink-p', `file-owner-p', `file-nlinks', `file-size', `file-modes', `file-modes-as-string', `set-file-modes', `file-modtime', `directory-files', `make-symlink', `read-symlink'. There are several undefined functions in this list. The `write-buffer-contents', `read-file-contents', and `insert-file-contents' pertain to the Jade text editor. The other two are defined as follows. - Operation: copy-file-to-local-fs file-name local-name Called when copying files between file handlers, this operation should copy the file matching the handler FILE-NAME, to the file on the local file system LOCAL-NAME. - Operation: copy-file-from-local-fs local-name file-name Called when copying files between file handlers, this operation should copy the local file FILE-NAME to the file matching the handler FILE-NAME. To prevent infinite recursion, while a particular operation is being processed by a file handler, that operation may not be passed back to the same handler. To allow file handlers to handle the `open-file' operation, it is possible to create file handles from arbitrary streams. - Function: make-file-from-stream file-name stream handler Return a new file object that refers to the logical file called FILE-NAME, that is not in the local filing system. All access to the file object will be directed through the stream object STREAM, and the file handler function HANDLER. An alternative method of opening remote files is to use a temporary file in the local file system with either one (`read' or `write' modes), or two (`append' mode) synchronisations with the remote system. This is the method used by the FTP remote file backend (see the next section). It has the advantage of simplifying the `seek-file' operation.  File: librep.info, Node: Remote Files, Prev: File Handlers, Up: Files Remote files ------------ Since one of the intentions for file handlers is to allow remote files to be accessed, a common method of providing new methods of doing this has been implemented, in the `remote.jl' Lisp library. Accessing a file name matching the regular expression: ^/(([a-zA-Z0-9._-]+)@)?([a-zA-Z0-9._-]+): for example `/john@host.com:file' refers to a file called `file' owned by the user `john', on the system `host.com'. If no username is specified explicitly, two variables are used to select the user: - Variable: remote-host-user-alist An alist mapping host regexps to the default user name to use for remote file connections to that host. - Variable: remote-default-user User name to use for remote file connections when otherwise unspecified. By default the current user name on the local system. Two variables control how individual hosts are matched to methods of accessing files. - Variable: remote-auto-backend-alist An alist of `(HOST-REGEXP . BACKEND-TYPE)' mapping host names to methods of accessing remote files. - Variable: remote-default-backend A symbol defining the method to use for otherwise unselected hosts. A method of accessing files, or a "backend" is a symbol whose `remote-backend' property names a function to call when files need to be accessed. For example the `ftp' backend is initialised as: (put 'ftp 'remote-backend remote-ftp-handler) The backend function is called as `(FUNCTION SPLIT-NAME OPERATION ARGS)'. The SPLIT-NAME is a three-element list, `(USER-OR-NIL HOST FILE)' defining the file to be accessed. The other options are as usual. Further details can be found in the `remote.jl', `remote-ftp.jl' and `remote-rcp.jl' Lisp source files. The `ftp' backend is currently the most well-developed, several functions and variables may be used to customise its behaviour. - Function: remote-ftp-add-passwd user host passwd Add the string PASSWD as the password for the FTP session connecting to USER@HOST. - Variable: remote-ftp-show-messages When true (the default), messages are displayed as FTP commands are executed. - Variable: remote-ftp-display-progress When true (the default) display progress of FTP transfers. - Variable: remote-ftp-anon-users A regular expression matching the user names for "anonymous" FTP sessions. - Variable: remote-ftp-anon-passwd The string to send as the passwd of an anonymous FTP session. By default the current uses email address. There is a problem with the `ftp' backend however; due to limitations in the FTP protocol, not all `librep' file operations are supported, with the most obvious exception being the `make-symlink' function. When this is a problem it may be possible to use rep's custom file transfer protocol. If it is possible to use `rsh' to connect to the remote host in question, then the `rep' backend may be used. The `rep-remote' program distributed with `librep' must exist on the remote host, this is executed via `rsh' and provides a protocol for executing all of `librep''s file operations on that host. See the `lisp/remote-rep.jl' file in the distribution for more details.  File: librep.info, Node: Processes, Next: Regular Expressions, Prev: Files, Up: The language Processes ========= When running on a Unix-style operating system `librep' allows you to launch and control an arbitrary number of subprocesses. These subprocesses can run either synchronously or asynchronously in respect to the Lisp system; data can be sent to the `stdin' channel and any output from the process is automatically written to a specified Lisp output stream. Unless otherwise stated, all functions and variables described in the following sections are exported by the `rep.io.processes' module. * Menu: * Process Objects:: Lisp objects associated with subprocesses * Asynchronous Processes:: Subprocesses running in parallel * Synchronous Processes:: Subprocesses which run to completion * Process I/O:: Input and output with subprocesses * Process States:: Suspending subprocesses * Signalling Processes:: Sending signals to subprocesses * Process Information:: Information stored in a process object  File: librep.info, Node: Process Objects, Next: Asynchronous Processes, Up: Processes Process Objects --------------- A "process object" is a type of Lisp object used to provide a link between a `physical' process running in the operating system and the Lisp system. Each process object consists of a number of values (references to other Lisp objects); these values are used when the object is used to run a subprocess. Process objects which aren't currently being used to run a subprocess store the exit value of the last subprocess which was run on that object. - Function: processp object This function returns true when its argument is a process object. The programmer-accessible components of a process object are, "Output stream" A normal Lisp output stream (*note Output Streams::), all data which the subprocess outputs to its `stdout' channel is copied to this output stream. *Note Process I/O::. "Error stream" A normal Lisp output stream (*note Output Streams::), all data which the subprocess outputs to its `stderr' channel is copied to this output stream. Unless explicitly specified error output goes to the `stdout' stream. *Note Process I/O::. "State change function" A Lisp function, called each time the state of the subprocess being run on the object changes. *Note Process States::. "Program name" The name of the program (a string) to execute when the subprocess is created. "Program arguments" A list of strings defining the arguments which the program executed is given. "Directory" When a subprocess is started its current working directory is set to the directory named by this component of its process object. "Connection type" Asynchronous subprocesses (*note Asynchronous Processes::) use this component to decide how to connect to the I/O channels of the subprocess. Current options include pseudo-terminals and pipes. - Function: make-process #!optional output-stream state-function directory program args This functions creates and returns a new process object. _No subprocess will be started._ The optional arguments are used to define the values of the components of the new process object, any undefined components will be set to default or null values. For each component of a process object two functions exist; one to read the component's value in a specific process object, the other to set the component's value. - Function: process-prog process Returns the value of the program name component of the process object PROCESS. - Function: set-process-prog process prog-name Sets the value of the program name component of the process object PROCESS to the string PROG-NAME, then returns PROG-NAME. - Function: process-args process Returns the value of the program arguments component of the process object PROCESS. - Function: set-process-args process arg-list Sets the value of the program arguments component of the process object PROCESS to the list ARG-LIST, then returns ARG-LIST. - Function: process-dir process Returns the value of the directory component of the process object PROCESS. - Function: set-process-dir process directory Sets the value of the directory component of the process object PROCESS to the string DIRECTORY, then returns DIRECTORY. - Variable: process-environment This is a list of environment variable definitions, as well as being used by the `setenv' and `getenv' functions (*note Environment Variables::), it also provides the environment of all started subprocesses. (car process-environment) => "LOGNAME=john" - Function: active-processes Returns a list containing all active (i.e. running or stopped) process objects.  File: librep.info, Node: Asynchronous Processes, Next: Synchronous Processes, Prev: Process Objects, Up: Processes Asynchronous Processes ---------------------- An "asynchronous process" is one that runs in parallel with Lisp evaluation, basically this means that once the subprocess has been started (by the `start-process' function) `librep' will carry on as normal. The event loop checks for output from asynchronous processes, any found is copied to the process' output stream, and calls the the process' state change function when necessary (*note Process States::). Alternatively the `accept-process-output' function can be called to explicitly allow output to be processed. When using asynchronous processes you have a choice as to the Unix mechanism used to connect the `stdin', `stdout' and `stderr' streams of the subprocess to `librep''s process. The two options currently available are pipes or pseudo-terminals; in general pseudo-terminals should only be used to provide a direct interface between the user and a process (i.e. the `*shell*' buffer) since they allow job control to work properly. At other times pipes will be more efficient and are used by default. However, there are cases where the buffering characteristics of pipes mean that ptys must be used. - Function: start-process #!optional process program #!rest args This function starts an asynchronous subprocess running on the process object PROCESS. If PROCESS is undefined a new process object is created (by calling the function `make-process' with all arguments undefined). The function always returns the process object which the subprocess has been started on. If for some reason the subprocess can't be created an error of type `process-error' is signalled. The optional argument PROGRAM is a string defining the name of the program to execute, it will be searched for in all the directories in the `PATH' environment variable. The ARGS are strings to pass to the subprocess as its arguments. When defined, the optional arguments overrule the values of the related components of the process object. The following example runs the `ls' program asynchronously, its output is sent to the `standard-output' stream. (let ((process (make-process standard-output))) (start-process process "ls" "-s")) Note that when `librep' exits it kills all of its asynchronous subprocesses which are still running without warning. - Function: process-connection-type process Returns the value of the connection type component of the process object PROCESS. See the documentation of the `set-process-connection-type' function for the values this may take. - Function: set-process-connection-type process symbol Sets the value of the connection type component of the process object PROCESS to SYMBOL, then returns SYMBOL. SYMBOL should be one of the following symbols, `pty' Use pseudo-terminals to connect to subprocesses running asynchronously on this process object. `pipe' Use standard Unix pipes to connect, this is the default value of this component. `socketpair' Uses a connected pair of sockets. Note that currently only the `pipe' connection type allows the normal and error output streams of the process to be separated.  File: librep.info, Node: Synchronous Processes, Next: Process I/O, Prev: Asynchronous Processes, Up: Processes Synchronous Processes --------------------- When a "synchronous process" is started `librep' waits for it to terminate before continuing; they are usually used when a Lisp program must invoke an external program as part of its function, i.e. the auto-compression feature runs the compression program `gzip' synchronously when it needs to compress a buffer. Unlike asynchronous processes their is no choice between pipes and pseudo-terminals for connecting to a subprocess. Instead, it is possible to link the `stdin' channel of a synchronous process to a named file. - Function: call-process #!optional process input-file-name program #!rest args This function starts a process running on the process object PROCESS. If PROCESS is undefined a new process object is created by calling the `make' function. If defined, the string INPUT-FILE-NAME names the file to connect to the standard input of the subprocess, otherwise the subprocess' input comes from the null device (`/dev/null' on UNIX). The optional arguments PROGRAM and ARGS define the name of the program to invoke and any arguments to pass to it. The program will be searched for in all directories listed in the `process-environment' variable. If any of the optional parameters are unspecified they should have been set in the PROCESS-OBJECT prior to calling this function. After successfully creating the new subprocess, this function simply copies any output from the process to the output stream defined by the output stream component of the process object. When the subprocess exits its exit-value is returned (an integer). Note that the exit-value is the value returned by the `process-exit-value' function, see *Note Process Information::. If, for some reason, the new subprocess can't be created an error of type `process-error' is signalled. The following function definition is taken from the `gzip.jl' file, it shows how the `call-process' function can be used to uncompress a file into a buffer (for Jade). ;; Uncompress FILE-NAME into the current buffer (defun gzip-uncompress (file-name) (let ((proc (make-process (current-buffer)))) (message (concat "Uncompressing `" file-name "'") t) ;; gunzip can do .Z files as well (unless (zerop (call-process proc nil "gunzip" "-c" file-name)) (signal 'file-error (list "Can't gunzip file" file-name))))) The user is able to interrupt synchronous subprocesses (for example if they seem to have got wedged somehow). Each time a user-interrupt is received by `librep' (i.e. the `INT' signal), a stronger signal is sent to the subprocess. First an interrupt signal, then a termination signal, before finally a non-ignoreable quit signal is sent.  File: librep.info, Node: Process I/O, Next: Process States, Prev: Synchronous Processes, Up: Processes Process I/O ----------- It is only possible for lisp programs to explicitly send input data to _asynchronous_ processes (by the time it's possible to call a function to send data to a synchronous process, the process will already have terminated!). Simply use the process object which an asynchronous process is running on as a normal Lisp input stream, any strings or characters written to the stream will immediately be copied to the `stdin' channel of the subprocess. With synchronous processes, the only control over input data possible is by giving the `call-process' function the name of a file containing the subprocess' input data. Output data from subprocesses is handled the same way by both asynchronous and synchronous processes: it is simply copied to the stream defined by the output stream component of the subprocess' process object. - Function: process-output-stream process Returns the value of the output stream component of the process object PROCESS. - Function: set-process-output-stream process stream Sets the value of the output stream component of the process object PROCESS to the stream STREAM, then returns STREAM. By default the `stdout' and `stderr' streams are combined, use the `set-process-error-stream' function to separate them. (Note that this currently only works with `pipe' connection types.) - Function: process-error-stream process Returns the value of the error stream component of the process object PROCESS. - Function: set-process-error-stream process stream Sets the value of the error stream component of the process object PROCESS to the stream STREAM, then returns STREAM. Output from asynchronous subprocesses (this includes changes of state as well as stream output) is only propagated at well-defined times. Either when in the read stage of the read-eval-print, or input, loop, or when the `accept-process-output' or `sit-for' functions are called. - Function: accept-process-output #!optional seconds milliseconds Wait SECONDS plus MILLISECONDS for output from any asynchronous subprocesses. If any arrives, process it, then return false. Otherwise return true. If either of the arguments is undefined, they count as zero in the addition. - Function: sit-for #!optional seconds milliseconds Wait for input to arrive and be processed. No more than SECONDS seconds plus MILLISECONDS milliseconds will be waited. If at the end of this time no input has arrived, return true. Otherwise return false if input was found. Note that this function is only distinct to `accept-process-output' when `librep' is embedded in another application, or an extension has been loaded that provides an event loop (such as the `gtk' binding). In this case other input forms, such as user input, for example, can preempt the timeout. This function is exported by the `rep.system' module. *Note Streams::.  File: librep.info, Node: Process States, Next: Signalling Processes, Prev: Process I/O, Up: Processes Process States -------------- Each process object has a "state" associated with it; this depends on the status of the subprocess currently running on the process object (or not as the case may be). The possible states are, "running" This state means that the subprocess using this process object is currently running, i.e. it hasn't been stopped. "stopped" Means that the subprocess has been temporarily suspended from running. "unused" This means that the process object is free to have a new subprocess created on it. Predicates exist which test whether a given process object is in one of these states. - Function: process-running-p process-object Returns true when PROCESS-OBJECT is in the running state. - Function: process-stopped-p process-object Returns true when PROCESS-OBJECT is in the stopped state. - Function: process-in-use-p process-object Returns true when PROCESS-OBJECT is _not_ in the unused state. The following two functions are used to stop and then subsequently continue a process running. - Function: stop-process process-object #!optional whole-group This function suspends execution of the subprocess running on the process object PROCESS-OBJECT. If WHOLE-GROUP is true all subprocesses in the process group of PROCESS-OBJECT are stopped. - Function: continue-process process-object #!optional whole-group Use this function to continue a subprocess executing after it has been stopped (by the `stop-process' function). If WHOLE-GROUP is true all subprocesses in the process group of PROCESS-OBJECT are continued. The state change function component of a process object defines a function which will be called each time the state of the process object changes. If your program needs to be informed when an asynchronous process terminates this function is the way to do it. - Function: process-function process Returns the value of the state change function component of the process object PROCESS. - Function: set-process-function process function Sets the value of the state change function component of the process object PROCESS to the function FUNCTION, then returns FUNCTION.  File: librep.info, Node: Signalling Processes, Next: Process Information, Prev: Process States, Up: Processes Signalling Processes -------------------- - Function: interrupt-process process-object #!optional whole-group Sends the `SIGINT' signal to PROCESS-OBJECT. - Function: kill-process process-object #!optional whole-group Sends the `SIGKILL' signal to the PROCESS-OBJECT. Note that the functions `stop-process' and `continue-process' also send signals to the subprocess. - Function: signal-process process signal #!optional whole-group Send the signal SIGNAL to the process PROCESS; if WHOLE-GROUP is true the signal is also sent to all processes in the process group of PROCESS. PROCESS may be either a Lisp process object, or an integer defining the pid of the process to signal (not necessarily started by `librep'). SIGNAL may either be an integer defining the actual signal number, or a symbol naming the signal. All names are as usual but with the preceding `SIG' removed, for example the `SIGINT' signal would be sent by using the symbol `INT'. If a named signal doesn't exist on the current operating system, an error is raised. Returns true if the signal was sent successfully. As with the UNIX `kill' system call, `signal-process' may also be used to test whether a process with a particular pid is currently active, by using a signal with value zero.  File: librep.info, Node: Process Information, Prev: Signalling Processes, Up: Processes Process Information ------------------- - Function: process-id process-object This function returns the operating-system identifier associated with the subprocess currently running on the process object PROCESS-OBJECT. - Function: process-exit-value process-object Returns the integer representing the return code of the last subprocess to be run on PROCESS-OBJECT. If no subprocess has been run on PROCESS-OBJECT, PROCESS-OBJECT is currently in the running state or the last subprocess exited abnormally (i.e. from a terminal signal) false is returned. - Function: process-exit-status process-object This function returns the integer that was the exit status of the last subprocess which was run on the process object PROCESS-OBJECT. Note that the exit status is _not_ the value given to the `exit' function in a C program, use the `process-exit-value' to access this value. If no process has been run on PROCESS-OBJECT, or the process is currently in the running state false is returned.  File: librep.info, Node: Regular Expressions, Next: Time and Date, Prev: Processes, Up: The language Regular Expressions =================== Regular expressions (or "regexps") are a powerful method of matching patterns in strings. `librep' uses the `regexp(3)' implementation by Henry Spencer, with some modifications that I have made. It comes with this banner: Copyright (c) 1986 by University of Toronto. Written by Henry Spencer. Not derived from licensed software. Permission is granted to anyone to use this software for any purpose on any computer system, and to redistribute it freely, subject to the following restrictions: 1. The author is not responsible for the consequences of use of this software, no matter how awful, even if they arise from defects in it. 2. The origin of this software must not be misrepresented, either by explicit claim or by omission. 3. Altered versions must be plainly marked as such, and must not be misrepresented as being the original software. * Menu: * Regexp Syntax:: How to write regular expressions * Regexp Functions:: How to use them  File: librep.info, Node: Regexp Syntax, Next: Regexp Functions, Up: Regular Expressions Regular Expression Syntax ------------------------- The syntax of a regular expression is as follows (this is adapted from the manual page): A regular expression is zero or more "branches", separated by `|'. It matches anything that matches one of the branches. A branch is zero or more "pieces", concatenated. It matches a match for the first, followed by a match for the second, etc. A piece is an "atom" possibly followed by `*', `+', or `?'. An atom followed by `*' matches a sequence of 0 or more matches of the atom. An atom followed by `+' matches a sequence of 1 or more matches of the atom. An atom followed by `?' matches a match of the atom, or the null string. An atom is a regular expression in parentheses (matching a match for the regular expression), a "range" (see below), `.' (matching any single character), `^' (matching the null string at the beginning of the input string), `$' (matching the null string at the end of the input string), one of the strings `\s', `\S', `\w', `\W', `\d', `\D', `\b', `\B', or a `\' followed by a single character (matching that character), or a single character with no other significance (matching that character). A "range" is a sequence of characters enclosed in `[]'. It normally matches any single character from the sequence. If the sequence begins with `^', it matches any single character _not_ from the rest of the sequence. If two characters in the sequence are separated by `-', this is shorthand for the full list of ASCII characters between them (e.g. `[0-9]' matches any decimal digit). To include a literal `]' in the sequence, make it the first character (following a possible `^'). To include a literal `-', make it the first or last character. Also, any of the `*', `+' or `?' operators can be suffixed by a `?' character (i.e. `*?', `+?', `??'). The meaning of the operator remains the same but it becomes "non-greedy". This means that it will match the _smallest_ number of characters satisfying the regular expression, instead of the default behaviour which is to match the _largest_. The backslash-introduced atoms have the following meanings: `\s' Match any whitespace character. `\S' Match any non-whitespace character. `\w' Match any alphanumeric or underscore character. `\W' Match any non-(alphanumeric or underscore) character. `\d' Match any numeric character. `\D' Match any non-numeric character. `\b' Match the null string between two adjacent `\w' and `\W' characters (in any order). `\B' Match the null string that is not between two adjacent `\w' and `\W' characters. Some example legal regular expressions could be: `ab*a+b' Matches an `a' followed by zero or more `b' characters, followed by one or more `a' characters, followed by a `b'. For example, `aaab', `abbbab', etc... `(one|two)_three' Matches `one_three' or `two_three'. `^cmd_[0-9]+' `^cmd_\d+' Matches `cmd_' followed by one or more digits, it must start at the beginning of the line.  File: librep.info, Node: Regexp Functions, Prev: Regexp Syntax, Up: Regular Expressions Regexp Functions ---------------- These functions are exported by the `rep.regexp' module. - Function: quote-regexp string Return a version of STRING, such that when used as a regexp, it will match the original contents of STRING verbatim, and nothing else. This involves quoting regexp meta-characters. (quote-regexp "abc") => "abc" (quote-regexp "a+c") => "a\\+c" - Function: string-match regexp string #!optional start ignore-case Returns true if the string STRING matches the regular expression REGEXP. The string matches if executing the regexp at _any_ position in the string succeeds. When defined, START is the index of the first character to start matching at (counting from zero). When IGNORE-CASE is true the case of matched strings are ignored. Note that character classes are still case-significant. (string-match "ab+c" "abbbc") => t (string-match "ab+c" "xxxabbbcyyy") => t - Function: string-looking-at regexp string #!optional start ignore-case Similar to `string-match', but only returns true if STRING matches REGEXP starting at the character at index START in the string (or the first character if START is undefined). (string-looking-at "ab+c" "abbbc" 0) => t (string-looking-at "ab+c" "xxxabbbcyyy" 0) => () (string-looking-at "ab+c" "xxxabbbcyyy" 3) => t - Function: match-start #!optional n Returns the position at which the N'th parenthesised expression started in the last successful regexp match. If N is false or zero the position of the start of the whole match is returned instead. When matching strings, all positions are integers, with the first character in the string represented by zero. However, extensions that allow regexps to be matched against other textual inputs may return different position values. (string-match "x*(foo|bar)y" "xxxbary") => t (match-start 1) => 3 - Function: match-end #!optional n Similar to `match-start', but returns the position of the character following the matched item. (string-match "x*(foo|bar)y" "xxxbary") => t (match-end 1) => 6 A common use of regular expressions is to match a string, then replace certain portions of the string with other text. - Function: expand-last-match template Expand the TEMPLATE substituting the parenthesised expressions from the most recent successfully matched regular expression. TEMPLATE may contain the following substitution-inducing escape sequences: `\0' `\&' Substitute the whole string matched by the last regexp `\N' Substitute the N'th parenthensised expression, where 1 <= N <= 9. `\\' Substitute a single backslash character. (string-match "x*(foo|bar)y" "xxxbary") => t (expand-last-match "test-\\1-ing") => "test-bar-ing" Note that double backslashes are required due to the read syntax of strings (*note Strings::). - Function: string-replace regexp template string Returns the string created by replacing all matches of REGEXP in STRING with the result of expanding TEMPLATE using the `expand-last-match' function. (string-replace "-" "_" "foo-bar-baz") => "foo_bar_baz" (string-replace "&(optional|rest)" "#!\\1" "(a &optional b &rest c)") => "(a #!optional b #!rest c)"  File: librep.info, Node: Time and Date, Next: i18n, Prev: Regular Expressions, Up: The language Time and Date ============= This section describes how time and date values are handled in `librep'. * Menu: * Timestamps:: Internal representation of time * Formatting Dates:: Creating strings from timestamps * Parsing Dates:: Reading textual dates  File: librep.info, Node: Timestamps, Next: Formatting Dates, Up: Time and Date Timestamps ---------- As in UNIX, `librep' measures time as the number of seconds since January 1st, 1970 (known as the "epoch"). For historical reasons rep stores timestamps as a pair of integers, using a cons cell. The first integer records the number of whole days since the epoch, the second records the number of seconds since the start of the day (in universal time). These function are exported by the `rep.system' module: - Function: current-time Return the number of seconds since the epoch, in a cons-cell. (current-time) => (10744 . 61063) - Function: fix-time timestamp Ensure that the two parts of TIMESTAMP (a pair or integers) are consistent, simply that the number of seconds is less than the number of seconds in a whole day. If not, the timestamp is adjusted to meet this constraint. - Function: time-later-p timestamp-1 timestamp-2 Returns true if TIMESTAMP-1 is later than TIMESTAMP-2. On the plus side, this scheme won't wrap around as quickly as UNIX's `time_t' will ;-) The `rep.util.time' module also provides some functions for manipulating timestamps: - Function: time->seconds timestamp Convert TIMESTAMP to an integer, the number of seconds since the epoch that it represents. - Function: seconds->time seconds Convert from an integer SECONDS to a timestamp object. - Function: time- timestamp-1 timestamp-2 Return the number of seconds difference between TIMESTAMP-1 and TIMESTAMP-2. - Constant: seconds-per-day The number of seconds in a 24-hour day.  File: librep.info, Node: Formatting Dates, Next: Parsing Dates, Prev: Timestamps, Up: Time and Date Formatting Dates ---------------- Given a timestamp value it is possible to format it as a string, in many different formats. - Function: current-time-string #!optional timestamp format Return a string defining TIMESTAMP according to the string FORMAT. If TIMESTAMP is undefined, the current time is used. The FORMAT string may include any of the formatting characters from the C library's `strftime(3)' function. If undefined a standard, fixed-width, format is used: (current-time-string) => "Wed Jun 2 18:07:53 1999" Some of the possible formatting substitutions include (this is copied from the GNU libc manual, *note (libc)Formatting Date and Time::): `%a' The abbreviated weekday name according to the current locale. `%A' The full weekday name according to the current locale. `%b' The abbreviated month name according to the current locale. `%B' The full month name according to the current locale. `%c' The preferred date and time representation for the current locale. `%d' The day of the month as a decimal number (range `01' to `31'). `%H' The hour as a decimal number, using a 24-hour clock (range `00' to `23'). `%I' The hour as a decimal number, using a 12-hour clock (range `01' to `12'). `%j' The day of the year as a decimal number (range `001' to `366'). `%m' The month as a decimal number (range `01' to `12'). `%M' The minute as a decimal number. `%p' Either `am' or `pm', according to the given time value; or the corresponding strings for the current locale. `%S' The second as a decimal number. `%U' The week number of the current year as a decimal number, starting with the first Sunday as the first day of the first week. `%W' The week number of the current year as a decimal number, starting with the first Monday as the first day of the first week. `%w' The day of the week as a decimal number, Sunday being `0'. `%x' The preferred date representation for the current locale, but without the time. `%X' The preferred time representation for the current locale, but with no date. `%y' The year as a decimal number, but without a century (range `00' to `99'). `%Y' The year as a decimal number, including the century. `%Z' The time zone or name or abbreviation (empty if the time zone can't be determined). `%%' A literal `%' character. (current-time-string nil "%Y-%m-%d") => "1999-06-02"  File: librep.info, Node: Parsing Dates, Prev: Formatting Dates, Up: Time and Date Parsing Dates ------------- The `date' Lisp library provides rudimentary support for parsing date and time descriptions to their individual components, and to timestamps. Evaluate the form `(require 'date)' to load this library. - Function: parse-date string #!optional start Returns a vector encoding the date described by STRING. If START is defined, it specifies the index of the character in the string to start parsing from. Each element of the vector contains a separate component of the overall point in time described by the string. The indices of these elements are defined by the following constants: `date-vec-day-abbrev' The abbreviated name of the day of the week. `date-vec-day' The numeric day of the month, counting from one. `date-vec-month-abbrev' The abbreviated name of the month. `date-vec-month' The numeric month of the year, counting from January equals one. `date-vec-year' The numeric year. `date-vec-hour' The numeric hour of the day. `date-vec-minute' The numeric minute of the hour. `date-vec-second' The numeric second of the minute. `date-vec-timezone' If true, a string defining the timezone. `date-vec-epoch-time' The timestamp (*note Timestamps::), including the effects of the timezone, if given. (current-time-string) => "Wed Jun 2 18:37:17 1999" (parse-date (current-time-string)) => ["Wed" 2 "Jun" 6 1999 18 37 17 0 (10744 . 67037)] (parse-date "1999-06-02") => ["Tue" 2 "Jun" 6 1999 0 0 0 0 (10744 . 0)] (parse-date "June 6, 1999") => ["" 0 "Jun" 6 1999 0 0 0 0 (10742 . 0)] (aref (parse-date "June 6, 1999") date-vec-epoch-time) => (10742 . 0) XXX provide more information on accepted formats, outputs for incomplete descriptions, etc...  File: librep.info, Node: i18n, Next: System Information, Prev: Time and Date, Up: The language Internationalisation ==================== `librep' has support for internationalisation (or i18n) of text messages, using the GNU `gettext' implementation (*note Overview: (gettext)Top.), a run-time library managing the mapping between text strings in the programmer's native language and in the language of the end user. Three functions are provided to access the message catalogues maintained by GNU `gettext'. Import the `rep.i18n.gettext' module to load them. - Function: _ string Attempt to find a native language equivalent of STRING. If no equivalent is found the original string is returned. Note that this function is always defined, even if the `gettext' module hasn't been required. In this case it always returns the original string. - Function: bindtextdomain domain directory Tell `gettext' that message catalogues for message domain DOMAIN (a string) can be found under the directory called DIRECTORY. - Function: textdomain domain Note that any strings that are to be translated in the future (until the next call to `textdomain') are in the domain called DOMAIN (a string). The usual method of constructing message catalogue templates (`.pot' files) is to run `xgettext' on the C source files of the program (that have been annotated for i18n). librep provides the `rep-xgettext' program to perform the same task for files of Lisp code.  File: librep.info, Node: System Information, Next: User Information, Prev: i18n, Up: The language System Information ================== These definitions are all exported by the `rep.system' module. - Variable: operating-system A symbol naming the current operating system. The only current option is `unix'. - Function: system-name This function returns a string naming the host that the interpreter is running on. When possible this be a fully-qualified name (i.e. including the domain) - Variable: rep-build-id A string describing the environment under which `librep' was built. This will always have the format `DATE by USER@HOST, for ARCH.'. rep-build-id => "Mon May 17 1999 by john@tizer.dcs.warwick.ac.uk, for sparc-sun-solaris2.6." - Variable: rep-version A string describing the current release of `librep'. rep-version => "1.0"  File: librep.info, Node: User Information, Next: Environment Variables, Prev: System Information, Up: The language User Information ================ These functions are exported by the `rep.system' module. - Function: user-login-name This function returns a string containing the login name of the user. (user-login-name) => "john" - Function: user-full-name #!optional real-name This function returns a string containing the `real' name of the user; the format of the string will depend on the host system. If REAL-NAME is a string, it defines the name that will be returned by subsequent calls to this function. (user-full-name) => "John Harper" - Function: user-home-directory #!optional user This function returns the home directory of the user whose login name is USER, or the current user if USER is undefined. The returned string will be as returned by `file-name-as-directory' (i.e. terminated by a `/' character under UNIX) (user-home-directory) => "/home/john/"  File: librep.info, Node: Environment Variables, Next: String Functions, Prev: User Information, Up: The language Environment Variables ===================== These functions are exported by the `rep.system' module. - Function: getenv variable-name This function returns the value (a string) of the environment variable called VARIABLE-NAME. If the specified variable doesn't exist false is returned. (getenv "OSTYPE") => "Linux" - Function: setenv variable-name new-value This function sets the value of the environment variable called VARIABLE-NAME to NEW-VALUE. NEW-VALUE can either be a string containing the new contents of the variable or false, in which case the environment variable is deleted. - Function: unsetenv variable-name Deletes any variable in `process-environment' named VARIABLE-NAME. See also *Note Process Objects:: for the description of the `process-environment' variable.  File: librep.info, Node: String Functions, Next: Sleeping, Prev: Environment Variables, Up: The language String Functions ================ - Function: translate-string string map Applies the MAP to each character in the STRING. MAP is also string, each character represents the translation for an ASCII character of that characters position in the string. If the string is less than 256 chars long any undefined characters will remain unchanged. For example, if STRING contains the character `A', with ASCII code 65, then it would be replaced by the 65th character in the string MAP. Note that the STRING really is modified, no copy is made - Variable: upcase-table A `translate-string' compatible translation map to convert lowercase characters to uppercase characters. - Variable: downcase-table A map to convert uppercase characters to lowercase. - Variable: flatten-table A translation map to convert newline characters to spaces. (translate-string "Foo" upcase-table) => "FOO" (translate-string "Foo" downcase-table) => "foo" - Function: complete-string template list #!optional ignore-case Return a string whose beginning matches the string TEMPLATE, and is unique in the set of all strings in LIST which also match TEMPLATE. If IGNORE-CASE is true, all matching ignores case of characters. (complete-string "foo" '("bar" "foobar" "forbarf" "foobat")) => "fooba" - Function: string-head-eq string-1 string-2 Returns t if STRING-2 matches the beginning of STRING-1. (string-head-eq "foobar" "foo") => t (string-head-eq "foo" "foobar") => () - Function: string-upper-case-p string Return true if STRING contains no lower case characters. - Function: string-lower-case-p string Return true if STRING contains no upper case characters. - Function: string-capitalized-p string Return true if the first character of STRING is upper case. - Function: string-upcase string Return a new string, an upper case copy of STRING. - Function: string-downcase string Return a new string, a lower case copy of STRING. - Function: capitalize-string string Return a new string, a copy of STRING with the first character in upper case. - Function: mapconcat function sequence separator Call FUNCTION for each member of SEQUENCE, concatenating the results. Between each pair of results, insert SEPARATOR. Return the resulting string.  File: librep.info, Node: Sleeping, Next: Beeping, Prev: String Functions, Up: The language Sleeping ======== - Function: sleep-for seconds #!optional milliseconds Pause for a SECONDS (plus the optional MILLISECONDS component) long period of time. Input becoming available will _not_ break the sleep (*note Process I/O::). This function is exported by the `rep.system' module.  File: librep.info, Node: Beeping, Next: Messages, Prev: Sleeping, Up: The language Beeping ======= Use this function to attract the user's attention. - Function: beep Ring a bell somewhere.  File: librep.info, Node: Messages, Next: Command Line Options, Prev: Beeping, Up: The language Messages ======== The `message' function will show the user a small message (typically no more than a single column of text). In graphical applications it _won't_ bring up a separate window, only displaying the text in a status bar or something similar. In a console-based environment, the message will be printed to the `stderr' stream, followed by a line break. - Function: message #!optional display-now Displays a one-line message, the string MESSAGE. If DISPLAY-NOW, every effort will be made to display the message as soon as possible, possibly before the next scheduled screen update (if applicable). This function is exported by the `rep.system' module.  File: librep.info, Node: Command Line Options, Next: Shell Commands, Prev: Messages, Up: The language Command Line Options ==================== As noted earlier any unused command line arguments are made available to scripts through the `command-line-args' variable (*note Invocation::). - Variable: command-line-args The list of unused command line arguments, in their original order. The `get-command-line-option' function may be used to scan this list of arguments. The `rep.system' module exports this function. - Function: get-command-line-option option #!optional requires-arg Returns t if OPTION was specified on the command line (OPTION is typically a phrase beginning with `--'). If REQUIRES-ARG is true, the option requires a parameter, the value of which is returned. If a parameter isn't supplied an error is signalled. (setq command-line-args '("--foo" "bar")) => ("--foo" "bar") (get-command-line-option "--foo" t) => "bar" command-line-args => () (setq command-line-args '("--foo=bar")) => ("--foo=bar") (get-command-line-option "--foo" t) => "bar" command-line-args => ()  File: librep.info, Node: Shell Commands, Next: Timers, Prev: Command Line Options, Up: The language Executing Shell Commands ======================== The subprocess handling of `librep' provides a comprehensive interface to starting and controlling external processes (*note Processes::). However it can be overkill when all that is required is to invoke a shell command, with its I/O going to the same places as the interpreter's. - Function: system command Execute the shell command COMMAND synchronously, returning its exit status. An error will be signalled if the shell process could not be started. The `stdin', `stdout' and `stderr' streams of the shell are left as in the interpreter process. The subprocesses environment is copied from the current value of the `process-environment' variable. Note that the exit status is _not_ the same as the return code of the command. It depends on the operating system, but under UNIX the return code can be found through right-shifting the exit status by eight bits. Low non-zero values represent that the process was killed by a signal. It is possible to interrupt a running shell process in the same way as with a normal synchronous process (*note Synchronous Processes::). Interrupt the interpreter, it will send progressively harder-to-ignore signals to the child each interrupt, until it is eventually terminated.  File: librep.info, Node: Timers, Next: Debugging, Prev: Shell Commands, Up: The language Asynchronous Timers =================== The `rep.io.timers' module (*note Modules::) allows a Lisp program to create multiple asynchronous timers, each of which is primed to call a specified function after a specified period of time. These functions only work when the Lisp event loop is being used (i.e. at least one `recursive-edit' is currently in progress). - Function: make-timer function #!optional seconds milliseconds Create and return a new timer object. It will be set to call the Lisp function FUNCTION after SECONDS seconds plus MILLISECONDS milliseconds. FUNCTION will be called with a single argument, the timer object that has just fired. If both SECONDS and MILLISECONDS are undefined, or zero, the timer will be created but won't call FUNCTION. After the time interval has passed, and FUNCTION has been called, the timer _will not_ be restarted. Use the `set-timer' function to reset it. - Function: delete-timer timer Prevent the timer object TIMER from calling the Lisp function associated with it. Use the `set-timer' function to reset it. - Function: set-timer timer #!optional seconds milliseconds Reset the timer object TIMER. If either/both of SECONDS and MILLISECONDS are defined the interval of the timer will be set to the specified time period. If neither are defined then the current interval of the timer is preserved.