This is Info file ../../info/lispref.info, produced by Makeinfo version 1.68 from the input file lispref.texi. INFO-DIR-SECTION XEmacs Editor START-INFO-DIR-ENTRY * Lispref: (lispref). XEmacs Lisp Reference Manual. END-INFO-DIR-ENTRY 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 XEmacs Lisp Reference Manual (for 19.14 and 20.0) v3.1, March 1996 XEmacs Lisp Reference Manual (for 19.15 and 20.1, 20.2, 20.3) v3.2, April, May, November 1997 XEmacs Lisp Reference Manual (for 21.0) v3.3, April 1998 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995, 1996 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: Auto Major Mode, Next: Mode Help, Prev: Example Major Modes, Up: Major Modes How XEmacs Chooses a Major Mode ------------------------------- Based on information in the file name or in the file itself, XEmacs automatically selects a major mode for the new buffer when a file is visited. - Command: fundamental-mode Fundamental mode is a major mode that is not specialized for anything in particular. Other major modes are defined in effect by comparison with this one--their definitions say what to change, starting from Fundamental mode. The `fundamental-mode' function does *not* run any hooks; you're not supposed to customize it. (If you want Emacs to behave differently in Fundamental mode, change the *global* state of Emacs.) - Command: normal-mode &optional FIND-FILE This function establishes the proper major mode and local variable bindings for the current buffer. First it calls `set-auto-mode', then it runs `hack-local-variables' to parse, and bind or evaluate as appropriate, any local variables. If the FIND-FILE argument to `normal-mode' is non-`nil', `normal-mode' assumes that the `find-file' function is calling it. In this case, it may process a local variables list at the end of the file and in the `-*-' line. The variable `enable-local-variables' controls whether to do so. If you run `normal-mode' interactively, the argument FIND-FILE is normally `nil'. In this case, `normal-mode' unconditionally processes any local variables list. *Note Local Variables in Files: (emacs)File variables, for the syntax of the local variables section of a file. `normal-mode' uses `condition-case' around the call to the major mode function, so errors are caught and reported as a `File mode specification error', followed by the original error message. - User Option: enable-local-variables This variable controls processing of local variables lists in files being visited. A value of `t' means process the local variables lists unconditionally; `nil' means ignore them; anything else means ask the user what to do for each file. The default value is `t'. - Variable: ignored-local-variables This variable holds a list of variables that should not be set by a local variables list. Any value specified for one of these variables is ignored. In addition to this list, any variable whose name has a non-`nil' `risky-local-variable' property is also ignored. - User Option: enable-local-eval This variable controls processing of `Eval:' in local variables lists in files being visited. A value of `t' means process them unconditionally; `nil' means ignore them; anything else means ask the user what to do for each file. The default value is `maybe'. - Function: set-auto-mode This function selects the major mode that is appropriate for the current buffer. It may base its decision on the value of the `-*-' line, on the visited file name (using `auto-mode-alist'), or on the value of a local variable. However, this function does not look for the `mode:' local variable near the end of a file; the `hack-local-variables' function does that. *Note How Major Modes are Chosen: (emacs)Choosing Modes. - User Option: default-major-mode This variable holds the default major mode for new buffers. The standard value is `fundamental-mode'. If the value of `default-major-mode' is `nil', XEmacs uses the (previously) current buffer's major mode for the major mode of a new buffer. However, if the major mode symbol has a `mode-class' property with value `special', then it is not used for new buffers; Fundamental mode is used instead. The modes that have this property are those such as Dired and Rmail that are useful only with text that has been specially prepared. - Function: set-buffer-major-mode BUFFER This function sets the major mode of BUFFER to the value of `default-major-mode'. If that variable is `nil', it uses the current buffer's major mode (if that is suitable). The low-level primitives for creating buffers do not use this function, but medium-level commands such as `switch-to-buffer' and `find-file-noselect' use it whenever they create buffers. - Variable: initial-major-mode The value of this variable determines the major mode of the initial `*scratch*' buffer. The value should be a symbol that is a major mode command name. The default value is `lisp-interaction-mode'. - Variable: auto-mode-alist This variable contains an association list of file name patterns (regular expressions; *note Regular Expressions::.) and corresponding major mode functions. Usually, the file name patterns test for suffixes, such as `.el' and `.c', but this need not be the case. An ordinary element of the alist looks like `(REGEXP . MODE-FUNCTION)'. For example, (("^/tmp/fol/" . text-mode) ("\\.texinfo\\'" . texinfo-mode) ("\\.texi\\'" . texinfo-mode) ("\\.el\\'" . emacs-lisp-mode) ("\\.c\\'" . c-mode) ("\\.h\\'" . c-mode) ...) When you visit a file whose expanded file name (*note File Name Expansion::.) matches a REGEXP, `set-auto-mode' calls the corresponding MODE-FUNCTION. This feature enables XEmacs to select the proper major mode for most files. If an element of `auto-mode-alist' has the form `(REGEXP FUNCTION t)', then after calling FUNCTION, XEmacs searches `auto-mode-alist' again for a match against the portion of the file name that did not match before. This match-again feature is useful for uncompression packages: an entry of the form `("\\.gz\\'" . FUNCTION)' can uncompress the file and then put the uncompressed file in the proper mode according to the name sans `.gz'. Here is an example of how to prepend several pattern pairs to `auto-mode-alist'. (You might use this sort of expression in your `.emacs' file.) (setq auto-mode-alist (append ;; File name starts with a dot. '(("/\\.[^/]*\\'" . fundamental-mode) ;; File name has no dot. ("[^\\./]*\\'" . fundamental-mode) ;; File name ends in `.C'. ("\\.C\\'" . c++-mode)) auto-mode-alist)) - Variable: interpreter-mode-alist This variable specifies major modes to use for scripts that specify a command interpreter in an `#!' line. Its value is a list of elements of the form `(INTERPRETER . MODE)'; for example, `("perl" . perl-mode)' is one element present by default. The element says to use mode MODE if the file specifies INTERPRETER. This variable is applicable only when the `auto-mode-alist' does not indicate which major mode to use. - Function: hack-local-variables &optional FORCE This function parses, and binds or evaluates as appropriate, any local variables for the current buffer. The handling of `enable-local-variables' documented for `normal-mode' actually takes place here. The argument FORCE usually comes from the argument FIND-FILE given to `normal-mode'.  File: lispref.info, Node: Mode Help, Next: Derived Modes, Prev: Auto Major Mode, Up: Major Modes Getting Help about a Major Mode ------------------------------- The `describe-mode' function is used to provide information about major modes. It is normally called with `C-h m'. The `describe-mode' function uses the value of `major-mode', which is why every major mode function needs to set the `major-mode' variable. - Command: describe-mode This function displays the documentation of the current major mode. The `describe-mode' function calls the `documentation' function using the value of `major-mode' as an argument. Thus, it displays the documentation string of the major mode function. (*Note Accessing Documentation::.) - Variable: major-mode This variable holds the symbol for the current buffer's major mode. This symbol should have a function definition that is the command to switch to that major mode. The `describe-mode' function uses the documentation string of the function as the documentation of the major mode.  File: lispref.info, Node: Derived Modes, Prev: Mode Help, Up: Major Modes Defining Derived Modes ---------------------- It's often useful to define a new major mode in terms of an existing one. An easy way to do this is to use `define-derived-mode'. - Macro: define-derived-mode VARIANT PARENT NAME DOCSTRING BODY... This construct defines VARIANT as a major mode command, using NAME as the string form of the mode name. The new command VARIANT is defined to call the function PARENT, then override certain aspects of that parent mode: * The new mode has its own keymap, named `VARIANT-map'. `define-derived-mode' initializes this map to inherit from `PARENT-map', if it is not already set. * The new mode has its own syntax table, kept in the variable `VARIANT-syntax-table'. `define-derived-mode' initializes this variable by copying `PARENT-syntax-table', if it is not already set. * The new mode has its own abbrev table, kept in the variable `VARIANT-abbrev-table'. `define-derived-mode' initializes this variable by copying `PARENT-abbrev-table', if it is not already set. * The new mode has its own mode hook, `VARIANT-hook', which it runs in standard fashion as the very last thing that it does. (The new mode also runs the mode hook of PARENT as part of calling PARENT.) In addition, you can specify how to override other aspects of PARENT with BODY. The command VARIANT evaluates the forms in BODY after setting up all its usual overrides, just before running `VARIANT-hook'. The argument DOCSTRING specifies the documentation string for the new mode. If you omit DOCSTRING, `define-derived-mode' generates a documentation string. Here is a hypothetical example: (define-derived-mode hypertext-mode text-mode "Hypertext" "Major mode for hypertext. \\{hypertext-mode-map}" (setq case-fold-search nil)) (define-key hypertext-mode-map [down-mouse-3] 'do-hyper-link)  File: lispref.info, Node: Minor Modes, Next: Modeline Format, Prev: Major Modes, Up: Modes Minor Modes =========== A "minor mode" provides features that users may enable or disable independently of the choice of major mode. Minor modes can be enabled individually or in combination. Minor modes would be better named "Generally available, optional feature modes" except that such a name is unwieldy. A minor mode is not usually a modification of single major mode. For example, Auto Fill mode may be used in any major mode that permits text insertion. To be general, a minor mode must be effectively independent of the things major modes do. A minor mode is often much more difficult to implement than a major mode. One reason is that you should be able to activate and deactivate minor modes in any order. A minor mode should be able to have its desired effect regardless of the major mode and regardless of the other minor modes in effect. Often the biggest problem in implementing a minor mode is finding a way to insert the necessary hook into the rest of XEmacs. Minor mode keymaps make this easier than it used to be. * Menu: * Minor Mode Conventions:: Tips for writing a minor mode. * Keymaps and Minor Modes:: How a minor mode can have its own keymap.  File: lispref.info, Node: Minor Mode Conventions, Next: Keymaps and Minor Modes, Up: Minor Modes Conventions for Writing Minor Modes ----------------------------------- There are conventions for writing minor modes just as there are for major modes. Several of the major mode conventions apply to minor modes as well: those regarding the name of the mode initialization function, the names of global symbols, and the use of keymaps and other tables. In addition, there are several conventions that are specific to minor modes. * Make a variable whose name ends in `-mode' to represent the minor mode. Its value should enable or disable the mode (`nil' to disable; anything else to enable.) We call this the "mode variable". This variable is used in conjunction with the `minor-mode-alist' to display the minor mode name in the modeline. It can also enable or disable a minor mode keymap. Individual commands or hooks can also check the variable's value. If you want the minor mode to be enabled separately in each buffer, make the variable buffer-local. * Define a command whose name is the same as the mode variable. Its job is to enable and disable the mode by setting the variable. The command should accept one optional argument. If the argument is `nil', it should toggle the mode (turn it on if it is off, and off if it is on). Otherwise, it should turn the mode on if the argument is a positive integer, a symbol other than `nil' or `-', or a list whose CAR is such an integer or symbol; it should turn the mode off otherwise. Here is an example taken from the definition of `transient-mark-mode'. It shows the use of `transient-mark-mode' as a variable that enables or disables the mode's behavior, and also shows the proper way to toggle, enable or disable the minor mode based on the raw prefix argument value. (setq transient-mark-mode (if (null arg) (not transient-mark-mode) (> (prefix-numeric-value arg) 0))) * Add an element to `minor-mode-alist' for each minor mode (*note Modeline Variables::.). This element should be a list of the following form: (MODE-VARIABLE STRING) Here MODE-VARIABLE is the variable that controls enabling of the minor mode, and STRING is a short string, starting with a space, to represent the mode in the modeline. These strings must be short so that there is room for several of them at once. When you add an element to `minor-mode-alist', use `assq' to check for an existing element, to avoid duplication. For example: (or (assq 'leif-mode minor-mode-alist) (setq minor-mode-alist (cons '(leif-mode " Leif") minor-mode-alist)))  File: lispref.info, Node: Keymaps and Minor Modes, Prev: Minor Mode Conventions, Up: Minor Modes Keymaps and Minor Modes ----------------------- Each minor mode can have its own keymap, which is active when the mode is enabled. To set up a keymap for a minor mode, add an element to the alist `minor-mode-map-alist'. *Note Active Keymaps::. One use of minor mode keymaps is to modify the behavior of certain self-inserting characters so that they do something else as well as self-insert. In general, this is the only way to do that, since the facilities for customizing `self-insert-command' are limited to special cases (designed for abbrevs and Auto Fill mode). (Do not try substituting your own definition of `self-insert-command' for the standard one. The editor command loop handles this function specially.)  File: lispref.info, Node: Modeline Format, Next: Hooks, Prev: Minor Modes, Up: Modes Modeline Format =============== Each Emacs window (aside from minibuffer windows) includes a modeline, which displays status information about the buffer displayed in the window. The modeline contains information about the buffer, such as its name, associated file, depth of recursive editing, and the major and minor modes. This section describes how the contents of the modeline are controlled. It is in the chapter on modes because much of the information displayed in the modeline relates to the enabled major and minor modes. `modeline-format' is a buffer-local variable that holds a template used to display the modeline of the current buffer. All windows for the same buffer use the same `modeline-format' and their modelines appear the same (except for scrolling percentages and line numbers). The modeline of a window is normally updated whenever a different buffer is shown in the window, or when the buffer's modified-status changes from `nil' to `t' or vice-versa. If you modify any of the variables referenced by `modeline-format' (*note Modeline Variables::.), you may want to force an update of the modeline so as to display the new information. - Function: redraw-modeline &optional ALL Force redisplay of the current buffer's modeline. If ALL is non-`nil', then force redisplay of all modelines. The modeline is usually displayed in inverse video. This is controlled using the `modeline' face. *Note Faces::. * Menu: * Modeline Data:: The data structure that controls the modeline. * Modeline Variables:: Variables used in that data structure. * %-Constructs:: Putting information into a modeline.  File: lispref.info, Node: Modeline Data, Next: Modeline Variables, Up: Modeline Format The Data Structure of the Modeline ---------------------------------- The modeline contents are controlled by a data structure of lists, strings, symbols, and numbers kept in the buffer-local variable `mode-line-format'. The data structure is called a "modeline construct", and it is built in recursive fashion out of simpler modeline constructs. The same data structure is used for constructing frame titles (*note Frame Titles::.). - Variable: modeline-format The value of this variable is a modeline construct with overall responsibility for the modeline format. The value of this variable controls which other variables are used to form the modeline text, and where they appear. A modeline construct may be as simple as a fixed string of text, but it usually specifies how to use other variables to construct the text. Many of these variables are themselves defined to have modeline constructs as their values. The default value of `modeline-format' incorporates the values of variables such as `mode-name' and `minor-mode-alist'. Because of this, very few modes need to alter `modeline-format'. For most purposes, it is sufficient to alter the variables referenced by `modeline-format'. A modeline construct may be a list, a symbol, or a string. If the value is a list, each element may be a list, a symbol, or a string. `STRING' A string as a modeline construct is displayed verbatim in the mode line except for "`%'-constructs". Decimal digits after the `%' specify the field width for space filling on the right (i.e., the data is left justified). *Note %-Constructs::. `SYMBOL' A symbol as a modeline construct stands for its value. The value of SYMBOL is used as a modeline construct, in place of SYMBOL. However, the symbols `t' and `nil' are ignored; so is any symbol whose value is void. There is one exception: if the value of SYMBOL is a string, it is displayed verbatim: the `%'-constructs are not recognized. `(STRING REST...) or (LIST REST...)' A list whose first element is a string or list means to process all the elements recursively and concatenate the results. This is the most common form of mode line construct. `(SYMBOL THEN ELSE)' A list whose first element is a symbol is a conditional. Its meaning depends on the value of SYMBOL. If the value is non-`nil', the second element, THEN, is processed recursively as a modeline element. But if the value of SYMBOL is `nil', the third element, ELSE, is processed recursively. You may omit ELSE; then the mode line element displays nothing if the value of SYMBOL is `nil'. `(WIDTH REST...)' A list whose first element is an integer specifies truncation or padding of the results of REST. The remaining elements REST are processed recursively as modeline constructs and concatenated together. Then the result is space filled (if WIDTH is positive) or truncated (to -WIDTH columns, if WIDTH is negative) on the right. For example, the usual way to show what percentage of a buffer is above the top of the window is to use a list like this: `(-3 "%p")'. If you do alter `modeline-format' itself, the new value should use the same variables that appear in the default value (*note Modeline Variables::.), rather than duplicating their contents or displaying the information in another fashion. This way, customizations made by the user or by Lisp programs (such as `display-time' and major modes) via changes to those variables remain effective. Here is an example of a `modeline-format' that might be useful for `shell-mode', since it contains the hostname and default directory. (setq modeline-format (list "" 'modeline-modified "%b--" (getenv "HOST") ; One element is not constant. ":" 'default-directory " " 'global-mode-string " %[(" 'mode-name 'modeline-process 'minor-mode-alist "%n" ")%]----" '(line-number-mode "L%l--") '(-3 . "%p") "-%-"))  File: lispref.info, Node: Modeline Variables, Next: %-Constructs, Prev: Modeline Data, Up: Modeline Format Variables Used in the Modeline ------------------------------ This section describes variables incorporated by the standard value of `modeline-format' into the text of the mode line. There is nothing inherently special about these variables; any other variables could have the same effects on the modeline if `modeline-format' were changed to use them. - Variable: modeline-modified This variable holds the value of the modeline construct that displays whether the current buffer is modified. The default value of `modeline-modified' is `("--%1*%1+-")'. This means that the modeline displays `--**-' if the buffer is modified, `-----' if the buffer is not modified, `--%%-' if the buffer is read only, and `--%*--' if the buffer is read only and modified. Changing this variable does not force an update of the modeline. - Variable: modeline-buffer-identification This variable identifies the buffer being displayed in the window. Its default value is `("%F: %17b")', which means that it usually displays `Emacs:' followed by seventeen characters of the buffer name. (In a terminal frame, it displays the frame name instead of `Emacs'; this has the effect of showing the frame number.) You may want to change this in modes such as Rmail that do not behave like a "normal" XEmacs. - Variable: global-mode-string This variable holds a modeline spec that appears in the mode line by default, just after the buffer name. The command `display-time' sets `global-mode-string' to refer to the variable `display-time-string', which holds a string containing the time and load information. The `%M' construct substitutes the value of `global-mode-string', but this is obsolete, since the variable is included directly in the modeline. - Variable: mode-name This buffer-local variable holds the "pretty" name of the current buffer's major mode. Each major mode should set this variable so that the mode name will appear in the modeline. - Variable: minor-mode-alist This variable holds an association list whose elements specify how the modeline should indicate that a minor mode is active. Each element of the `minor-mode-alist' should be a two-element list: (MINOR-MODE-VARIABLE MODELINE-STRING) More generally, MODELINE-STRING can be any mode line spec. It appears in the mode line when the value of MINOR-MODE-VARIABLE is non-`nil', and not otherwise. These strings should begin with spaces so that they don't run together. Conventionally, the MINOR-MODE-VARIABLE for a specific mode is set to a non-`nil' value when that minor mode is activated. The default value of `minor-mode-alist' is: minor-mode-alist => ((vc-mode vc-mode) (abbrev-mode " Abbrev") (overwrite-mode overwrite-mode) (auto-fill-function " Fill") (defining-kbd-macro " Def") (isearch-mode isearch-mode)) `minor-mode-alist' is not buffer-local. The variables mentioned in the alist should be buffer-local if the minor mode can be enabled separately in each buffer. - Variable: modeline-process This buffer-local variable contains the modeline information on process status in modes used for communicating with subprocesses. It is displayed immediately following the major mode name, with no intervening space. For example, its value in the `*shell*' buffer is `(": %s")', which allows the shell to display its status along with the major mode as: `(Shell: run)'. Normally this variable is `nil'. - Variable: default-modeline-format This variable holds the default `modeline-format' for buffers that do not override it. This is the same as `(default-value 'modeline-format)'. The default value of `default-modeline-format' is: ("" modeline-modified modeline-buffer-identification " " global-mode-string " %[(" mode-name modeline-process minor-mode-alist "%n" ")%]----" (line-number-mode "L%l--") (-3 . "%p") "-%-") - Variable: vc-mode The variable `vc-mode', local in each buffer, records whether the buffer's visited file is maintained with version control, and, if so, which kind. Its value is `nil' for no version control, or a string that appears in the mode line.  File: lispref.info, Node: %-Constructs, Prev: Modeline Variables, Up: Modeline Format `%'-Constructs in the ModeLine ------------------------------ The following table lists the recognized `%'-constructs and what they mean. In any construct except `%%', you can add a decimal integer after the `%' to specify how many characters to display. `%b' The current buffer name, obtained with the `buffer-name' function. *Note Buffer Names::. `%f' The visited file name, obtained with the `buffer-file-name' function. *Note Buffer File Name::. `%F' The name of the selected frame. `%c' The current column number of point. `%l' The current line number of point. `%*' `%' if the buffer is read only (see `buffer-read-only'); `*' if the buffer is modified (see `buffer-modified-p'); `-' otherwise. *Note Buffer Modification::. `%+' `*' if the buffer is modified (see `buffer-modified-p'); `%' if the buffer is read only (see `buffer-read-only'); `-' otherwise. This differs from `%*' only for a modified read-only buffer. *Note Buffer Modification::. `%&' `*' if the buffer is modified, and `-' otherwise. `%s' The status of the subprocess belonging to the current buffer, obtained with `process-status'. *Note Process Information::. `%l' the current line number. `%S' the name of the selected frame; this is only meaningful under the X Window System. *Note Frame Name::. `%t' Whether the visited file is a text file or a binary file. (This is a meaningful distinction only on certain operating systems.) `%p' The percentage of the buffer text above the *top* of window, or `Top', `Bottom' or `All'. `%P' The percentage of the buffer text that is above the *bottom* of the window (which includes the text visible in the window, as well as the text above the top), plus `Top' if the top of the buffer is visible on screen; or `Bottom' or `All'. `%n' `Narrow' when narrowing is in effect; nothing otherwise (see `narrow-to-region' in *Note Narrowing::). `%[' An indication of the depth of recursive editing levels (not counting minibuffer levels): one `[' for each editing level. *Note Recursive Editing::. `%]' One `]' for each recursive editing level (not counting minibuffer levels). `%%' The character `%'--this is how to include a literal `%' in a string in which `%'-constructs are allowed. `%-' Dashes sufficient to fill the remainder of the modeline. The following two `%'-constructs are still supported, but they are obsolete, since you can get the same results with the variables `mode-name' and `global-mode-string'. `%m' The value of `mode-name'. `%M' The value of `global-mode-string'. Currently, only `display-time' modifies the value of `global-mode-string'.  File: lispref.info, Node: Hooks, Prev: Modeline Format, Up: Modes Hooks ===== A "hook" is a variable where you can store a function or functions to be called on a particular occasion by an existing program. XEmacs provides hooks for the sake of customization. Most often, hooks are set up in the `.emacs' file, but Lisp programs can set them also. *Note Standard Hooks::, for a list of standard hook variables. Most of the hooks in XEmacs are "normal hooks". These variables contain lists of functions to be called with no arguments. The reason most hooks are normal hooks is so that you can use them in a uniform way. You can usually tell when a hook is a normal hook, because its name ends in `-hook'. The recommended way to add a hook function to a normal hook is by calling `add-hook' (see below). The hook functions may be any of the valid kinds of functions that `funcall' accepts (*note What Is a Function::.). Most normal hook variables are initially void; `add-hook' knows how to deal with this. As for abnormal hooks, those whose names end in `-function' have a value that is a single function. Those whose names end in `-hooks' have a value that is a list of functions. Any hook that is abnormal is abnormal because a normal hook won't do the job; either the functions are called with arguments, or their values are meaningful. The name shows you that the hook is abnormal and that you should look at its documentation string to see how to use it properly. Major mode functions are supposed to run a hook called the "mode hook" as the last step of initialization. This makes it easy for a user to customize the behavior of the mode, by overriding the local variable assignments already made by the mode. But hooks are used in other contexts too. For example, the hook `suspend-hook' runs just before XEmacs suspends itself (*note Suspending XEmacs::.). Here's an expression that uses a mode hook to turn on Auto Fill mode when in Lisp Interaction mode: (add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill) The next example shows how to use a hook to customize the way XEmacs formats C code. (People often have strong personal preferences for one format or another.) Here the hook function is an anonymous lambda expression. (add-hook 'c-mode-hook (function (lambda () (setq c-indent-level 4 c-argdecl-indent 0 c-label-offset -4 c-continued-statement-indent 0 c-brace-offset 0 comment-column 40)))) (setq c++-mode-hook c-mode-hook) The final example shows how the appearance of the modeline can be modified for a particular class of buffers only. (add-hook 'text-mode-hook (function (lambda () (setq modeline-format '(modeline-modified "Emacs: %14b" " " default-directory " " global-mode-string "%[(" mode-name minor-mode-alist "%n" modeline-process ") %]---" (-3 . "%p") "-%-"))))) At the appropriate time, XEmacs uses the `run-hooks' function to run particular hooks. This function calls the hook functions you have added with `add-hooks'. - Function: run-hooks &rest HOOKVAR This function takes one or more hook variable names as arguments, and runs each hook in turn. Each HOOKVAR argument should be a symbol that is a hook variable. These arguments are processed in the order specified. If a hook variable has a non-`nil' value, that value may be a function or a list of functions. If the value is a function (either a lambda expression or a symbol with a function definition), it is called. If it is a list, the elements are called, in order. The hook functions are called with no arguments. For example, here's how `emacs-lisp-mode' runs its mode hook: (run-hooks 'emacs-lisp-mode-hook) - Function: add-hook HOOK FUNCTION &optional APPEND LOCAL This function is the handy way to add function FUNCTION to hook variable HOOK. The argument FUNCTION may be any valid Lisp function with the proper number of arguments. For example, (add-hook 'text-mode-hook 'my-text-hook-function) adds `my-text-hook-function' to the hook called `text-mode-hook'. You can use `add-hook' for abnormal hooks as well as for normal hooks. It is best to design your hook functions so that the order in which they are executed does not matter. Any dependence on the order is "asking for trouble." However, the order is predictable: normally, FUNCTION goes at the front of the hook list, so it will be executed first (barring another `add-hook' call). If the optional argument APPEND is non-`nil', the new hook function goes at the end of the hook list and will be executed last. If LOCAL is non-`nil', that says to make the new hook function local to the current buffer. Before you can do this, you must make the hook itself buffer-local by calling `make-local-hook' (*not* `make-local-variable'). If the hook itself is not buffer-local, then the value of LOCAL makes no difference--the hook function is always global. - Function: remove-hook HOOK FUNCTION &optional LOCAL This function removes FUNCTION from the hook variable HOOK. If LOCAL is non-`nil', that says to remove FUNCTION from the local hook list instead of from the global hook list. If the hook itself is not buffer-local, then the value of LOCAL makes no difference. - Function: make-local-hook HOOK This function makes the hook variable `hook' local to the current buffer. When a hook variable is local, it can have local and global hook functions, and `run-hooks' runs all of them. This function works by making `t' an element of the buffer-local value. That serves as a flag to use the hook functions in the default value of the hook variable as well as those in the local value. Since `run-hooks' understands this flag, `make-local-hook' works with all normal hooks. It works for only some non-normal hooks--those whose callers have been updated to understand this meaning of `t'. Do not use `make-local-variable' directly for hook variables; it is not sufficient.  File: lispref.info, Node: Documentation, Next: Files, Prev: Modes, Up: Top Documentation ************* XEmacs Lisp has convenient on-line help facilities, most of which derive their information from the documentation strings associated with functions and variables. This chapter describes how to write good documentation strings for your Lisp programs, as well as how to write programs to access documentation. Note that the documentation strings for XEmacs are not the same thing as the XEmacs manual. Manuals have their own source files, written in the Texinfo language; documentation strings are specified in the definitions of the functions and variables they apply to. A collection of documentation strings is not sufficient as a manual because a good manual is not organized in that fashion; it is organized in terms of topics of discussion. * Menu: * Documentation Basics:: Good style for doc strings. Where to put them. How XEmacs stores them. * Accessing Documentation:: How Lisp programs can access doc strings. * Keys in Documentation:: Substituting current key bindings. * Describing Characters:: Making printable descriptions of non-printing characters and key sequences. * Help Functions:: Subroutines used by XEmacs help facilities. * Obsoleteness:: Upgrading Lisp functionality over time.  File: lispref.info, Node: Documentation Basics, Next: Accessing Documentation, Up: Documentation Documentation Basics ==================== A documentation string is written using the Lisp syntax for strings, with double-quote characters surrounding the text of the string. This is because it really is a Lisp string object. The string serves as documentation when it is written in the proper place in the definition of a function or variable. In a function definition, the documentation string follows the argument list. In a variable definition, the documentation string follows the initial value of the variable. When you write a documentation string, make the first line a complete sentence (or two complete sentences) since some commands, such as `apropos', show only the first line of a multi-line documentation string. Also, you should not indent the second line of a documentation string, if you have one, because that looks odd when you use `C-h f' (`describe-function') or `C-h v' (`describe-variable'). *Note Documentation Tips::. Documentation strings may contain several special substrings, which stand for key bindings to be looked up in the current keymaps when the documentation is displayed. This allows documentation strings to refer to the keys for related commands and be accurate even when a user rearranges the key bindings. (*Note Accessing Documentation::.) Within the Lisp world, a documentation string is accessible through the function or variable that it describes: * The documentation for a function is stored in the function definition itself (*note Lambda Expressions::.). The function `documentation' knows how to extract it. * The documentation for a variable is stored in the variable's property list under the property name `variable-documentation'. The function `documentation-property' knows how to extract it. To save space, the documentation for preloaded functions and variables (including primitive functions and autoloaded functions) is stored in the "internal doc file" `DOC'. The documentation for functions and variables loaded during the XEmacs session from byte-compiled files is stored in those very same byte-compiled files (*note Docs and Compilation::.). XEmacs does not keep documentation strings in memory unless necessary. Instead, XEmacs maintains, for preloaded symbols, an integer offset into the internal doc file, and for symbols loaded from byte-compiled files, a list containing the filename of the byte-compiled file and an integer offset, in place of the documentation string. The functions `documentation' and `documentation-property' use that information to read the documentation from the appropriate file; this is transparent to the user. For information on the uses of documentation strings, see *Note Help: (emacs)Help. The `emacs/lib-src' directory contains two utilities that you can use to print nice-looking hardcopy for the file `emacs/etc/DOC-VERSION'. These are `sorted-doc.c' and `digest-doc.c'.  File: lispref.info, Node: Accessing Documentation, Next: Keys in Documentation, Prev: Documentation Basics, Up: Documentation Access to Documentation Strings =============================== - Function: documentation-property SYMBOL PROPERTY &optional VERBATIM This function returns the documentation string that is recorded in SYMBOL's property list under property PROPERTY. It retrieves the text from a file if necessary, and runs `substitute-command-keys' to substitute actual key bindings. (This substitution is not done if VERBATIM is non-`nil'; the VERBATIM argument exists only as of Emacs 19.) (documentation-property 'command-line-processed 'variable-documentation) => "t once command line has been processed" (symbol-plist 'command-line-processed) => (variable-documentation 188902) - Function: documentation FUNCTION &optional VERBATIM This function returns the documentation string of FUNCTION. It reads the text from a file if necessary. Then (unless VERBATIM is non-`nil') it calls `substitute-command-keys', to return a value containing the actual (current) key bindings. The function `documentation' signals a `void-function' error if FUNCTION has no function definition. However, it is ok if the function definition has no documentation string. In that case, `documentation' returns `nil'. Here is an example of using the two functions, `documentation' and `documentation-property', to display the documentation strings for several symbols in a `*Help*' buffer. (defun describe-symbols (pattern) "Describe the XEmacs Lisp symbols matching PATTERN. All symbols that have PATTERN in their name are described in the `*Help*' buffer." (interactive "sDescribe symbols matching: ") (let ((describe-func (function (lambda (s) ;; Print description of symbol. (if (fboundp s) ; It is a function. (princ (format "%s\t%s\n%s\n\n" s (if (commandp s) (let ((keys (where-is-internal s))) (if keys (concat "Keys: " (mapconcat 'key-description keys " ")) "Keys: none")) "Function") (or (documentation s) "not documented")))) (if (boundp s) ; It is a variable. (princ (format "%s\t%s\n%s\n\n" s (if (user-variable-p s) "Option " "Variable") (or (documentation-property s 'variable-documentation) "not documented"))))))) sym-list) ;; Build a list of symbols that match pattern. (mapatoms (function (lambda (sym) (if (string-match pattern (symbol-name sym)) (setq sym-list (cons sym sym-list)))))) ;; Display the data. (with-output-to-temp-buffer "*Help*" (mapcar describe-func (sort sym-list 'string<)) (print-help-return-message)))) The `describe-symbols' function works like `apropos', but provides more information. (describe-symbols "goal") ---------- Buffer: *Help* ---------- goal-column Option *Semipermanent goal column for vertical motion, as set by C-x C-n, or nil. set-goal-column Command: C-x C-n Set the current horizontal position as a goal for C-n and C-p. Those commands will move to this position in the line moved to rather than trying to keep the same horizontal position. With a non-nil argument, clears out the goal column so that C-n and C-p resume vertical motion. The goal column is stored in the variable `goal-column'. temporary-goal-column Variable Current goal column for vertical motion. It is the column where point was at the start of current run of vertical motion commands. When the `track-eol' feature is doing its job, the value is 9999. ---------- Buffer: *Help* ---------- - Function: Snarf-documentation FILENAME This function is used only during XEmacs initialization, just before the runnable XEmacs is dumped. It finds the file offsets of the documentation strings stored in the file FILENAME, and records them in the in-core function definitions and variable property lists in place of the actual strings. *Note Building XEmacs::. XEmacs finds the file FILENAME in the `lib-src' directory. When the dumped XEmacs is later executed, the same file is found in the directory `doc-directory'. The usual value for FILENAME is `DOC', but this can be changed by modifying the variable `internal-doc-file-name'. - Variable: internal-doc-file-name This variable holds the name of the file containing documentation strings of built-in symbols, usually `DOC'. The full pathname of the internal doc file is `(concat doc-directory internal-doc-file-name)'. - Variable: doc-directory This variable holds the name of the directory which contains the "internal doc file" that contains documentation strings for built-in and preloaded functions and variables. In most cases, this is the same as `exec-directory'. They may be different when you run XEmacs from the directory where you built it, without actually installing it. See `exec-directory' in *Note Help Functions::. In older Emacs versions, `exec-directory' was used for this. - Variable: data-directory This variable holds the name of the directory in which XEmacs finds certain system independent documentation and text files that come with XEmacs. In older Emacs versions, `exec-directory' was used for this.