Linux Cubed Series 2: Applications

home *** CD-ROM | disk | FTP | other *** search

/ Linux Cubed Series 2: Applications / Linux Cubed Series 2 - Applications.iso / editors / emacs / xemacs / xemacs-1.006 / xemacs-1 / lib / xemacs-19.13 / info / lispref.info-36 < prev next >

Wrap

GNU Info File | 1995-09-01 | 47.7 KB | 1,116 lines

This is Info file ../../info/lispref.info, produced by Makeinfo-1.63 from the input file lispref.texi. Edition History: GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp Programmer's Manual (for 19.13) Third Edition, July 1995 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995 Amdahl Corporation. Copyright (C) 1995 Ben Wing. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English. File: lispref.info, Node: I18N Level 3, Next: I18N Level 4, Prev: I18N Levels 1 and 2, Up: Internationalization I18N Level 3 ============ * Menu: * Level 3 Basics:: * Level 3 Primitives:: * Dynamic Messaging:: * Domain Specification:: * Documentation String Extraction:: File: lispref.info, Node: Level 3 Basics, Next: Level 3 Primitives, Up: I18N Level 3 Level 3 Basics -------------- XEmacs now provides alpha-level functionality for I18N Level 3. This means that everything necessary for full messaging is available, but not every file has been converted. The two message files which have been created are `src/emacs.po' and `lisp/packages/mh-e.po'. Both files need to be converted using `msgfmt', and the resulting `.mo' files placed in some locale's `LC_MESSAGES' directory. The test "translations" in these files are the original messages prefixed by `TRNSLT_'. The domain for a variable is stored on the variable's property list under the property name VARIABLE-DOMAIN. The function `documentation-property' uses this information when translating a variable's documentation. File: lispref.info, Node: Level 3 Primitives, Next: Dynamic Messaging, Prev: Level 3 Basics, Up: I18N Level 3 Level 3 Primitives ------------------ - Function: gettext STRING This function looks up STRING in the default message domain and returns its translation. If `I18N3' was not enabled when XEmacs was compiled, it just returns STRING. - Function: dgettext DOMAIN STRING This function looks up STRING in the specified message domain and returns its translation. If `I18N3' was not enabled when XEmacs was compiled, it just returns STRING. - Function: bind-text-domain DOMAIN PATHNAME This function associates a pathname with a message domain. Here's how the path to message file is constructed under SunOS 5.x: `{pathname}/{LANG}/LC_MESSAGES/{domain}.mo' If `I18N3' was not enabled when XEmacs was compiled, this function does nothing. - Special Form: domain STRING This function specifies the text domain used for translating documentation strings and interactive prompts of a function. For example, write: (defun foo (arg) "Doc string" (domain "emacs-foo") ...) to specify `emacs-foo' as the text domain of the function `foo'. The "call" to `domain' is actually a declaration rather than a function; when actually called, `domain' just returns `nil' - Function: domain-of FUNCTION This function returns the text domain of FUNCTION; it returns `nil' if it is the default domain. If `I18N3' was not enabled when XEmacs was compiled, it always returns `nil'. File: lispref.info, Node: Dynamic Messaging, Next: Domain Specification, Prev: Level 3 Primitives, Up: I18N Level 3 Dynamic Messaging ----------------- The `format' function has been extended to permit you to change the order of parameter insertion. For example, the conversion format `%1$s' inserts parameter one as a string, while `%2$s' inserts parameter two. This is useful when creating translations which require you to change the word order. File: lispref.info, Node: Domain Specification, Next: Documentation String Extraction, Prev: Dynamic Messaging, Up: I18N Level 3 Domain Specification -------------------- The default message domain of XEmacs is `emacs'. For add-on packages, it is best to use a different domain. For example, let us say we want to convert the "gorilla" package to use the domain `emacs-gorilla'. To translate the message "What gorilla?", use `dgettext' as follows: (dgettext "emacs-gorilla" "What gorilla?") A function (or macro) which has a documentation string or an interactive prompt needs to be associated with the domain in order for the documentation or prompt to be translated. This is done with the `domain' special form as follows: (defun scratch (location) "Scratch the specified location." (domain "emacs-gorilla") (interactive "sScratch: ") ... ) It is most efficient to specify the domain in the first line of of the function body, before the `interactive' form. For variables and constants which have documentation strings, specify the domain after the documentation. - Special Form: defvar SYMBOL [VALUE [DOC-STRING [DOMAIN]]] Example: (defvar weight 250 "Weight of gorilla, in pounds." "emacs-gorilla") - Special Form: defconst SYMBOL [VALUE [DOC-STRING [DOMAIN]]] Example: (defconst limbs 4 "Number of limbs" "emacs-gorilla") Autoloaded functions which are specified in `loaddefs.el' do not need to have a domain specification, because their documentation strings are extracted into the main message base. However, for autoloaded functions which are specified in a separate package, use following syntax: - Function: autoload SYMBOL FILENAME &optional DOCSTRING INTERACTIVE MACRO DOMAIN Example: (autoload 'explore "jungle" "Explore the jungle." nil nil "emacs-gorilla") File: lispref.info, Node: Documentation String Extraction, Prev: Domain Specification, Up: I18N Level 3 Documentation String Extraction ------------------------------- The utility `etc/make-po' scans the file `DOC' to extract documentation strings and creates a message file `doc.po'. This file may then be inserted within `emacs.po'. Currently, `make-po' is hard-coded to read from `DOC' and write to `doc.po'. In order to extract documentation strings from an add-on package, first run `make-docfile' on the package to produce the `DOC' file. Then run `make-po -p' with the `-p' argument to indicate that we are extracting documentation for an add-on package. (The `-p' argument is a kludge to make up for a subtle difference between pre-loaded documentation and add-on documentation: For add-on packages, the final carriage returns in the strings produced by `make-docfile' must be ignored.) File: lispref.info, Node: I18N Level 4, Prev: I18N Level 3, Up: Internationalization I18N Level 4 ============ Not yet documented. File: lispref.info, Node: Tips, Next: XEmacs Internals, Prev: Internationalization, Up: Top Tips and Standards ****************** This chapter describes no additional features of Emacs Lisp. Instead it gives advice on making effective use of the features described in the previous chapters. * Menu: * Style Tips:: Writing clean and robust programs. * Compilation Tips:: Making compiled code run fast. * Documentation Tips:: Writing readable documentation strings. * Comment Tips:: Conventions for writing comments. * Library Headers:: Standard headers for library packages. File: lispref.info, Node: Style Tips, Next: Compilation Tips, Up: Tips Writing Clean Lisp Programs =========================== Here are some tips for avoiding common errors in writing Lisp code intended for widespread use: * Since all global variables share the same name space, and all functions share another name space, you should choose a short word to distinguish your program from other Lisp programs. Then take care to begin the names of all global variables, constants, and functions with the chosen prefix. This helps avoid name conflicts. This recommendation applies even to names for traditional Lisp primitives that are not primitives in Emacs Lisp--even to `cadr'. Believe it or not, there is more than one plausible way to define `cadr'. Play it safe; append your name prefix to produce a name like `foo-cadr' or `mylib-cadr' instead. If you write a function that you think ought to be added to Emacs under a certain name, such as `twiddle-files', don't call it by that name in your program. Call it `mylib-twiddle-files' in your program, and send mail to `bug-gnu-emacs@prep.ai.mit.edu' suggesting we add it to Emacs. If and when we do, we can change the name easily enough. If one prefix is insufficient, your package may use two or three alternative common prefixes, so long as they make sense. Separate the prefix from the rest of the symbol name with a hyphen, `-'. This will be consistent with XEmacs itself and with most Emacs Lisp programs. * It is often useful to put a call to `provide' in each separate library program, at least if there is more than one entry point to the program. * If a file requires certain other library programs to be loaded beforehand, then the comments at the beginning of the file should say so. Also, use `require' to make sure they are loaded. * If one file FOO uses a macro defined in another file BAR, FOO should contain this expression before the first use of the macro: (eval-when-compile (require 'BAR)) (And BAR should contain `(provide 'BAR)', to make the `require' work.) This will cause BAR to be loaded when you byte-compile FOO. Otherwise, you risk compiling FOO without the necessary macro loaded, and that would produce compiled code that won't work right. *Note Compiling Macros::. Using `eval-when-compile' avoids loading BAR when the compiled version of FOO is *used*. * If you define a major mode, make sure to run a hook variable using `run-hooks', just as the existing major modes do. *Note Hooks::. * If the purpose of a function is to tell you whether a certain condition is true or false, give the function a name that ends in `p'. If the name is one word, add just `p'; if the name is multiple words, add `-p'. Examples are `framep' and `frame-live-p'. * If a user option variable records a true-or-false condition, give it a name that ends in `-flag'. * Please do not define `C-c LETTER' as a key in your major modes. These sequences are reserved for users; they are the *only* sequences reserved for users, so we cannot do without them. Instead, define sequences consisting of `C-c' followed by a non-letter. These sequences are reserved for major modes. Changing all the major modes in Emacs 18 so they would follow this convention was a lot of work. Abandoning this convention would make that work go to waste, and inconvenience users. * Sequences consisting of `C-c' followed by `{', `}', `<', `>', `:' or `;' are also reserved for major modes. * Sequences consisting of `C-c' followed by any other punctuation character are allocated for minor modes. Using them in a major mode is not absolutely prohibited, but if you do that, the major mode binding may be shadowed from time to time by minor modes. * You should not bind `C-h' following any prefix character (including `C-c'). If you don't bind `C-h', it is automatically available as a help character for listing the subcommands of the prefix character. * You should not bind a key sequence ending in ESC except following another ESC. (That is, it is ok to bind a sequence ending in `ESC ESC'.) The reason for this rule is that a non-prefix binding for ESC in any context prevents recognition of escape sequences as function keys in that context. * Applications should not bind mouse events based on button 1 with the shift key held down. These events include `S-mouse-1', `M-S-mouse-1', `C-S-mouse-1', and so on. They are reserved for users. * Modes should redefine `mouse-2' as a command to follow some sort of reference in the text of a buffer, if users usually would not want to alter the text in that buffer by hand. Modes such as Dired, Info, Compilation, and Occur redefine it in this way. * When a package provides a modification of ordinary Emacs behavior, it is good to include a command to enable and disable the feature, Provide a command named `WHATEVER-mode' which turns the feature on or off, and make it autoload (*note Autoload::.). Design the package so that simply loading it has no visible effect--that should not enable the feature. Users will request the feature by invoking the command. * It is a bad idea to define aliases for the Emacs primitives. Use the standard names instead. * Redefining an Emacs primitive is an even worse idea. It may do the right thing for a particular program, but there is no telling what other programs might break as a result. * If a file does replace any of the functions or library programs of standard XEmacs, prominent comments at the beginning of the file should say which functions are replaced, and how the behavior of the replacements differs from that of the originals. * Please keep the names of your Emacs Lisp source files to 13 characters or less. This way, if the files are compiled, the compiled files' names will be 14 characters or less, which is short enough to fit on all kinds of Unix systems. * Don't use `next-line' or `previous-line' in programs; nearly always, `forward-line' is more convenient as well as more predictable and robust. *Note Text Lines::. * Don't call functions that set the mark, unless setting the mark is one of the intended features of your program. The mark is a user-level feature, so it is incorrect to change the mark except to supply a value for the user's benefit. *Note The Mark::. In particular, don't use these functions: * `beginning-of-buffer', `end-of-buffer' * `replace-string', `replace-regexp' If you just want to move point, or replace a certain string, without any of the other features intended for interactive users, you can replace these functions with one or two lines of simple Lisp code. * Use lists rather than vectors, except when there is a particular reason to use a vector. Lisp has more facilities for manipulating lists than for vectors, and working with lists is usually more convenient. Vectors are advantageous for tables that are substantial in size and are accessed in random order (not searched front to back), provided there is no need to insert or delete elements (only lists allow that). * The recommended way to print a message in the echo area is with the `message' function, not `princ'. *Note The Echo Area::. * When you encounter an error condition, call the function `error' (or `signal'). The function `error' does not return. *Note Signaling Errors::. Do not use `message', `throw', `sleep-for', or `beep' to report errors. * An error message should start with a capital letter but should not end with a period. * Try to avoid using recursive edits. Instead, do what the Rmail `e' command does: use a new local keymap that contains one command defined to switch back to the old local keymap. Or do what the `edit-options' command does: switch to another buffer and let the user switch back at will. *Note Recursive Editing::. * In some other systems there is a convention of choosing variable names that begin and end with `*'. We don't use that convention in Emacs Lisp, so please don't use it in your programs. (Emacs uses such names only for program-generated buffers.) The users will find Emacs more coherent if all libraries use the same conventions. * Indent each function with `C-M-q' (`indent-sexp') using the default indentation parameters. * Don't make a habit of putting close-parentheses on lines by themselves; Lisp programmers find this disconcerting. Once in a while, when there is a sequence of many consecutive close-parentheses, it may make sense to split them in one or two significant places. * Please put a copyright notice on the file if you give copies to anyone. Use the same lines that appear at the top of the Lisp files in XEmacs itself. If you have not signed papers to assign the copyright to the Foundation, then place your name in the copyright notice in place of the Foundation's name. File: lispref.info, Node: Compilation Tips, Next: Documentation Tips, Prev: Style Tips, Up: Tips Tips for Making Compiled Code Fast ================================== Here are ways of improving the execution speed of byte-compiled Lisp programs. * Use the `profile' library to profile your program. See the file `profile.el' for instructions. * Use iteration rather than recursion whenever possible. Function calls are slow in Emacs Lisp even when a compiled function is calling another compiled function. * Using the primitive list-searching functions `memq', `member', `assq', or `assoc' is even faster than explicit iteration. It may be worth rearranging a data structure so that one of these primitive search functions can be used. * Certain built-in functions are handled specially in byte-compiled code, avoiding the need for an ordinary function call. It is a good idea to use these functions rather than alternatives. To see whether a function is handled specially by the compiler, examine its `byte-compile' property. If the property is non-`nil', then the function is handled specially. For example, the following input will show you that `aref' is compiled specially (*note Array Functions::.) while `elt' is not (*note Sequence Functions::.): (get 'aref 'byte-compile) => byte-compile-two-args (get 'elt 'byte-compile) => nil * If calling a small function accounts for a substantial part of your program's running time, make the function inline. This eliminates the function call overhead. Since making a function inline reduces the flexibility of changing the program, don't do it unless it gives a noticeable speedup in something slow enough that users care about the speed. *Note Inline Functions::. File: lispref.info, Node: Documentation Tips, Next: Comment Tips, Prev: Compilation Tips, Up: Tips Tips for Documentation Strings ============================== Here are some tips for the writing of documentation strings. * Every command, function, or variable intended for users to know about should have a documentation string. * An internal variable or subroutine of a Lisp program might as well have a documentation string. In earlier Emacs versions, you could save space by using a comment instead of a documentation string, but that is no longer the case. * The first line of the documentation string should consist of one or two complete sentences that stand on their own as a summary. `M-x apropos' displays just the first line, and if it doesn't stand on its own, the result looks bad. In particular, start the first line with a capital letter and end with a period. The documentation string can have additional lines that expand on the details of how to use the function or variable. The additional lines should be made up of complete sentences also, but they may be filled if that looks good. * For consistency, phrase the verb in the first sentence of a documentation string as an infinitive with "to" omitted. For instance, use "Return the cons of A and B." in preference to "Returns the cons of A and B." Usually it looks good to do likewise for the rest of the first paragraph. Subsequent paragraphs usually look better if they have proper subjects. * Write documentation strings in the active voice, not the passive, and in the present tense, not the future. For instance, use "Return a list containing A and B." instead of "A list containing A and B will be returned." * Avoid using the word "cause" (or its equivalents) unnecessarily. Instead of, "Cause Emacs to display text in boldface," write just "Display text in boldface." * Do not start or end a documentation string with whitespace. * Format the documentation string so that it fits in an Emacs window on an 80-column screen. It is a good idea for most lines to be no wider than 60 characters. The first line can be wider if necessary to fit the information that ought to be there. However, rather than simply filling the entire documentation string, you can make it much more readable by choosing line breaks with care. Use blank lines between topics if the documentation string is long. * *Do not* indent subsequent lines of a documentation string so that the text is lined up in the source code with the text of the first line. This looks nice in the source code, but looks bizarre when users view the documentation. Remember that the indentation before the starting double-quote is not part of the string! * A variable's documentation string should start with `*' if the variable is one that users would often want to set interactively. If the value is a long list, or a function, or if the variable would be set only in init files, then don't start the documentation string with `*'. *Note Defining Variables::. * The documentation string for a variable that is a yes-or-no flag should start with words such as "Non-nil means...", to make it clear that all non-`nil' values are equivalent and indicate explicitly what `nil' and non-`nil' mean. * When a function's documentation string mentions the value of an argument of the function, use the argument name in capital letters as if it were a name for that value. Thus, the documentation string of the function `/' refers to its second argument as `DIVISOR', because the actual argument name is `divisor'. Also use all caps for meta-syntactic variables, such as when you show the decomposition of a list or vector into subunits, some of which may vary. * When a documentation string refers to a Lisp symbol, write it as it would be printed (which usually means in lower case), with single-quotes around it. For example: `lambda'. There are two exceptions: write t and nil without single-quotes. (In this manual, we normally do use single-quotes for those symbols.) * Don't write key sequences directly in documentation strings. Instead, use the `\\[...]' construct to stand for them. For example, instead of writing `C-f', write `\\[forward-char]'. When Emacs displays the documentation string, it substitutes whatever key is currently bound to `forward-char'. (This is normally `C-f', but it may be some other character if the user has moved key bindings.) *Note Keys in Documentation::. * In documentation strings for a major mode, you will want to refer to the key bindings of that mode's local map, rather than global ones. Therefore, use the construct `\\<...>' once in the documentation string to specify which key map to use. Do this before the first use of `\\[...]'. The text inside the `\\<...>' should be the name of the variable containing the local keymap for the major mode. It is not practical to use `\\[...]' very many times, because display of the documentation string will become slow. So use this to describe the most important commands in your major mode, and then use `\\{...}' to display the rest of the mode's keymap. File: lispref.info, Node: Comment Tips, Next: Library Headers, Prev: Documentation Tips, Up: Tips Tips on Writing Comments ======================== We recommend these conventions for where to put comments and how to indent them: `;' Comments that start with a single semicolon, `;', should all be aligned to the same column on the right of the source code. Such comments usually explain how the code on the same line does its job. In Lisp mode and related modes, the `M-;' (`indent-for-comment') command automatically inserts such a `;' in the right place, or aligns such a comment if it is already present. This and following examples are taken from the Emacs sources. (setq base-version-list ; there was a base (assoc (substring fn 0 start-vn) ; version to which file-version-assoc-list)) ; this looks like ; a subversion `;;' Comments that start with two semicolons, `;;', should be aligned to the same level of indentation as the code. Such comments usually describe the purpose of the following lines or the state of the program at that point. For example: (prog1 (setq auto-fill-function ... ... ;; update modeline (redraw-modeline))) Every function that has no documentation string (because it is use only internally within the package it belongs to), should have instead a two-semicolon comment right before the function, explaining what the function does and how to call it properly. Explain precisely what each argument means and how the function interprets its possible values. `;;;' Comments that start with three semicolons, `;;;', should start at the left margin. Such comments are used outside function definitions to make general statements explaining the design principles of the program. For example: ;;; This Lisp code is run in XEmacs ;;; when it is to operate as a server ;;; for other processes. Another use for triple-semicolon comments is for commenting out lines within a function. We use triple-semicolons for this precisely so that they remain at the left margin. (defun foo (a) ;;; This is no longer necessary. ;;; (force-mode-line-update) (message "Finished with %s" a)) `;;;;' Comments that start with four semicolons, `;;;;', should be aligned to the left margin and are used for headings of major sections of a program. For example: ;;;; The kill ring The indentation commands of the Lisp modes in XEmacs, such as `M-;' (`indent-for-comment') and TAB (`lisp-indent-line') automatically indent comments according to these conventions, depending on the the number of semicolons. *Note Manipulating Comments: (emacs)Comments. File: lispref.info, Node: Library Headers, Prev: Comment Tips, Up: Tips Conventional Headers for XEmacs Libraries ========================================= XEmacs has conventions for using special comments in Lisp libraries to divide them into sections and give information such as who wrote them. This section explains these conventions. First, an example: ;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers ;; Copyright (C) 1992 Free Software Foundation, Inc. ;; Author: Eric S. Raymond <esr@snark.thyrsus.com> ;; Maintainer: Eric S. Raymond <esr@snark.thyrsus.com> ;; Created: 14 Jul 1992 ;; Version: 1.2 ;; Keywords: docs ;; This file is part of XEmacs. COPYING PERMISSIONS... The very first line should have this format: ;;; FILENAME --- DESCRIPTION The description should be complete in one line. After the copyright notice come several "header comment" lines, each beginning with `;; HEADER-NAME:'. Here is a table of the conventional possibilities for HEADER-NAME: `Author' This line states the name and net address of at least the principal author of the library. If there are multiple authors, you can list them on continuation lines led by `;;' and a tab character, like this: ;; Author: Ashwin Ram <Ram-Ashwin@cs.yale.edu> ;; Dave Sill <de5@ornl.gov> ;; Dave Brennan <brennan@hal.com> ;; Eric Raymond <esr@snark.thyrsus.com> `Maintainer' This line should contain a single name/address as in the Author line, or an address only, or the string `FSF'. If there is no maintainer line, the person(s) in the Author field are presumed to be the maintainers. The example above is mildly bogus because the maintainer line is redundant. The idea behind the `Author' and `Maintainer' lines is to make possible a Lisp function to "send mail to the maintainer" without having to mine the name out by hand. Be sure to surround the network address with `<...>' if you include the person's full name as well as the network address. `Created' This optional line gives the original creation date of the file. For historical interest only. `Version' If you wish to record version numbers for the individual Lisp program, put them in this line. `Adapted-By' In this header line, place the name of the person who adapted the library for installation (to make it fit the style conventions, for example). `Keywords' This line lists keywords for the `finder-by-keyword' help command. This field is important; it's how people will find your package when they're looking for things by topic area. To separate the keywords, you can use spaces, commas, or both. Just about every Lisp library ought to have the `Author' and `Keywords' header comment lines. Use the others if they are appropriate. You can also put in header lines with other header names--they have no standard meanings, so they can't do any harm. We use additional stylized comments to subdivide the contents of the library file. Here is a table of them: `;;; Commentary:' This begins introductory comments that explain how the library works. It should come right after the copying permissions. `;;; Change log:' This begins change log information stored in the library file (if you store the change history there). For most of the Lisp files distributed with XEmacs, the change history is kept in the file `ChangeLog' and not in the source file at all; these files do not have a `;;; Change log:' line. `;;; Code:' This begins the actual code of the program. `;;; FILENAME ends here' This is the "footer line"; it appears at the very end of the file. Its purpose is to enable people to detect truncated versions of the file from the lack of a footer line. File: lispref.info, Node: XEmacs Internals, Next: Standard Errors, Prev: Tips, Up: Top XEmacs Internals **************** This chapter describes how the runnable XEmacs executable is dumped with the preloaded Lisp libraries in it, how storage is allocated, and some internal aspects of XEmacs that may be of interest to C programmers. * Menu: * Building XEmacs:: How to preload Lisp libraries into XEmacs. * Pure Storage:: A kludge to make preloaded Lisp functions sharable. * Garbage Collection:: Reclaiming space for Lisp objects no longer used. * Writing XEmacs Primitives:: Writing C code for XEmacs. * Object Internals:: Data formats of buffers, windows, processes. File: lispref.info, Node: Building XEmacs, Next: Pure Storage, Prev: XEmacs Internals, Up: XEmacs Internals Building XEmacs =============== This section explains the steps involved in building the XEmacs executable. You don't have to know this material to build and install XEmacs, since the makefiles do all these things automatically. This information is pertinent to XEmacs maintenance. Compilation of the C source files in the `src' directory produces an executable file called `temacs', also called a "bare impure XEmacs". It contains the Emacs Lisp interpreter and I/O routines, but not the editing commands. The command `temacs -l loadup' uses `temacs' to create the real runnable XEmacs executable. These arguments direct `temacs' to evaluate the Lisp files specified in the file `loadup.el'. These files set up the normal XEmacs editing environment, resulting in an XEmacs that is still impure but no longer bare. It takes a substantial time to load the standard Lisp files. Luckily, you don't have to do this each time you run XEmacs; `temacs' can dump out an executable program called `emacs' that has these files preloaded. `emacs' starts more quickly because it does not need to load the files. This is the XEmacs executable that is normally installed. To create `emacs', use the command `temacs -batch -l loadup dump'. The purpose of `-batch' here is to prevent `temacs' from trying to initialize any of its data on the terminal; this ensures that the tables of terminal information are empty in the dumped XEmacs. The argument `dump' tells `loadup.el' to dump a new executable named `emacs'. Some operating systems don't support dumping. On those systems, you must start XEmacs with the `temacs -l loadup' command each time you use it. This takes a substantial time, but since you need to start Emacs once a day at most--or once a week if you never log out--the extra time is not too severe a problem. You can specify additional files to preload by writing a library named `site-load.el' that loads them. You may need to increase the value of `PURESIZE', in `src/puresize.h', to make room for the additional files. (Try adding increments of 20000 until it is big enough.) However, the advantage of preloading additional files decreases as machines get faster. On modern machines, it is usually not advisable. You can specify other Lisp expressions to execute just before dumping by putting them in a library named `site-init.el'. However, if they might alter the behavior that users expect from an ordinary unmodified XEmacs, it is better to put them in `default.el', so that users can override them if they wish. *Note Start-up Summary::. Before `loadup.el' dumps the new executable, it finds the documentation strings for primitive and preloaded functions (and variables) in the file where they are stored, by calling `Snarf-documentation' (*note Accessing Documentation::.). These strings were moved out of the `emacs' executable to make it smaller. *Note Documentation Basics::. - Function: dump-emacs TO-FILE FROM-FILE This function dumps the current state of XEmacs into an executable file TO-FILE. It takes symbols from FROM-FILE (this is normally the executable file `temacs'). If you use this function in an XEmacs that was already dumped, you must set `command-line-processed' to `nil' first for good results. *Note Command Line Arguments::. - Command: emacs-version This function returns a string describing the version of XEmacs that is running. It is useful to include this string in bug reports. (emacs-version) => "XEmacs 19.13 of Mon Aug 21 1995 on willow (usg-unix-v) [formerly Lucid Emacs]" Called interactively, the function prints the same information in the echo area. - Variable: emacs-build-time The value of this variable is the time at which XEmacs was built at the local site. emacs-build-time => "Tue Jun 6 14:55:57 1995" - Variable: emacs-version The value of this variable is the version of Emacs being run. It is a string, e.g. `"19.13 XEmacs Lucid"'. The following two variables did not exist before Emacs version 19.23, which reduces their usefulness at present, but we hope they will be convenient in the future. - Variable: emacs-major-version The major version number of Emacs, as an integer. For XEmacs version 19.13, the value is 19. - Variable: emacs-minor-version The minor version number of Emacs, as an integer. For XEmacs version 19.13, the value is 13. File: lispref.info, Node: Pure Storage, Next: Garbage Collection, Prev: Building XEmacs, Up: XEmacs Internals Pure Storage ============ Emacs Lisp uses two kinds of storage for user-created Lisp objects: "normal storage" and "pure storage". Normal storage is where all the new data created during an XEmacs session is kept; see the following section for information on normal storage. Pure storage is used for certain data in the preloaded standard Lisp files--data that should never change during actual use of XEmacs. Pure storage is allocated only while `temacs' is loading the standard preloaded Lisp libraries. In the file `emacs', it is marked as read-only (on operating systems that permit this), so that the memory space can be shared by all the XEmacs jobs running on the machine at once. Pure storage is not expandable; a fixed amount is allocated when XEmacs is compiled, and if that is not sufficient for the preloaded libraries, `temacs' crashes. If that happens, you must increase the compilation parameter `PURESIZE' in the file `src/puresize.h'. This normally won't happen unless you try to preload additional libraries or add features to the standard ones. - Function: purecopy OBJECT This function makes a copy of OBJECT in pure storage and returns it. It copies strings by simply making a new string with the same characters in pure storage. It recursively copies the contents of vectors and cons cells. It does not make copies of other objects such as symbols, but just returns them unchanged. It signals an error if asked to copy markers. This function is a no-op except while XEmacs is being built and dumped; it is usually called only in the file `emacs/lisp/loaddefs.el', but a few packages call it just in case you decide to preload them. - Variable: pure-bytes-used The value of this variable is the number of bytes of pure storage allocated so far. Typically, in a dumped XEmacs, this number is very close to the total amount of pure storage available--if it were not, we would preallocate less. - Variable: purify-flag This variable determines whether `defun' should make a copy of the function definition in pure storage. If it is non-`nil', then the function definition is copied into pure storage. This flag is `t' while loading all of the basic functions for building XEmacs initially (allowing those functions to be sharable and non-collectible). Dumping XEmacs as an executable always writes `nil' in this variable, regardless of the value it actually has before and after dumping. You should not change this flag in a running XEmacs. File: lispref.info, Node: Garbage Collection, Next: Writing XEmacs Primitives, Prev: Pure Storage, Up: XEmacs Internals Garbage Collection ================== When a program creates a list or the user defines a new function (such as by loading a library), that data is placed in normal storage. If normal storage runs low, then XEmacs asks the operating system to allocate more memory in blocks of 1k bytes. Each block is used for one type of Lisp object, so symbols, cons cells, markers, etc., are segregated in distinct blocks in memory. (Vectors, long strings, buffers and certain other editing types, which are fairly large, are allocated in individual blocks, one per object, while small strings are packed into blocks of 8k bytes.) It is quite common to use some storage for a while, then release it by (for example) killing a buffer or deleting the last pointer to an object. XEmacs provides a "garbage collector" to reclaim this abandoned storage. (This name is traditional, but "garbage recycler" might be a more intuitive metaphor for this facility.) The garbage collector operates by finding and marking all Lisp objects that are still accessible to Lisp programs. To begin with, it assumes all the symbols, their values and associated function definitions, and any data presently on the stack, are accessible. Any objects that can be reached indirectly through other accessible objects are also accessible. When marking is finished, all objects still unmarked are garbage. No matter what the Lisp program or the user does, it is impossible to refer to them, since there is no longer a way to reach them. Their space might as well be reused, since no one will miss them. The second ("sweep") phase of the garbage collector arranges to reuse them. The sweep phase puts unused cons cells onto a "free list" for future allocation; likewise for symbols and markers. It compacts the accessible strings so they occupy fewer 8k blocks; then it frees the other 8k blocks. Vectors, buffers, windows, and other large objects are individually allocated and freed using `malloc' and `free'. Common Lisp note: unlike other Lisps, Emacs Lisp does not call the garbage collector when the free list is empty. Instead, it simply requests the operating system to allocate more storage, and processing continues until `gc-cons-threshold' bytes have been used. This means that you can make sure that the garbage collector will not run during a certain portion of a Lisp program by calling the garbage collector explicitly just before it (provided that portion of the program does not use so much space as to force a second garbage collection). - Command: garbage-collect This command runs a garbage collection, and returns information on the amount of space in use. (Garbage collection can also occur spontaneously if you use more than `gc-cons-threshold' bytes of Lisp data since the previous garbage collection.) `garbage-collect' returns a list containing the following information: ((USED-CONSES . FREE-CONSES) (USED-SYMS . FREE-SYMS) (USED-MARKERS . FREE-MARKERS) USED-STRING-CHARS USED-VECTOR-SLOTS (PLIST)) (garbage-collect) => ((7285 . 3680) (5462 . 0) (47 . 1074) 135506 20902 (conses-used 7285 conses-free 3680 cons-storage 88064 symbols-used 5462 symbols-free 0 symbol-storage 133120 vectors-used 1005 vectors-total-length 20902 vector-storage 95668 bytecodes-used 508 bytecodes-free 30 bytecode-storage 16192 short-strings-used 3596 long-strings-used 0 strings-free 920 short-strings-total-length 135506 short-string-storage 163840 long-strings-total-length 0 string-header-storage 55296 floats-used 0 floats-free 9 float-storage 2044 markers-used 47 markers-free 1074 marker-storage 18360 events-used 104 events-free 21 event-storage 15840 extents-used 0 extents-free 17 extent-storage 2032 extent-duplicates-used 0 extent-duplicates-free 0 extent-duplicate-storage 0 processs-used 1 process-storage 80 frames-used 1 frame-storage 188 menubar-datas-used 1 menubar-data-storage 24 pixmaps-used 10 pixmap-storage 560 faces-used 44 face-storage 1232 pixels-used 14 pixel-storage 448 fonts-used 7 font-storage 280 tooltalk-patterns-used 23 tooltalk-pattern-storage 368 cursors-used 5 cursor-storage 160 buffer-local-value-cells-used 33 buffer-local-value-cell-storage 1056 keymaps-used 128 keymap-storage 5120 hashtables-used 256 hashtable-storage 9216 buffers-used 11 buffers-freed 1 buffer-storage 2640 output-streams-used 0 output-streams-freed 1 output-stream-storage 0 windows-used 4 windows-freed 12 window-storage 576 window-configurations-used 0 window-configurations-freed 22 window-configuration-storage 0)) Here is a table explaining each element: USED-CONSES The number of cons cells in use. FREE-CONSES The number of cons cells for which space has been obtained from the operating system, but that are not currently being used. USED-SYMS The number of symbols in use. FREE-SYMS The number of symbols for which space has been obtained from the operating system, but that are not currently being used. USED-MARKERS The number of markers in use. FREE-MARKERS The number of markers for which space has been obtained from the operating system, but that are not currently being used. USED-STRING-CHARS The total size of all strings, in characters. USED-VECTOR-SLOTS The total number of elements of existing vectors. PLIST A list of alternating keyword/value pairs providing more detailed information. (As you can see above, quite a lot of information is provided.) - User Option: gc-cons-threshold The value of this variable is the number of bytes of storage that must be allocated for Lisp objects after one garbage collection in order to trigger another garbage collection. A cons cell counts as eight bytes, a string as one byte per character plus a few bytes of overhead, and so on; space allocated to the contents of buffers does not count. Note that the subsequent garbage collection does not happen immediately when the threshold is exhausted, but only the next time the Lisp evaluator is called. The initial threshold value is 300,000. If you specify a larger value, garbage collection will happen less often. This reduces the amount of time spent garbage collecting, but increases total memory use. You may want to do this when running a program that creates lots of Lisp data. You can make collections more frequent by specifying a smaller value, down to 10,000. A value less than 10,000 will remain in effect only until the subsequent garbage collection, at which time `garbage-collect' will set the threshold back to 10,000. - Function: memory-limit This function returns the address of the last byte XEmacs has allocated, divided by 1024. We divide the value by 1024 to make sure it fits in a Lisp integer. You can use this to get a general idea of how your actions affect the memory usage.