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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: Major Mode Conventions, Next: Example Major Modes, Up: Major Modes Major Mode Conventions ---------------------- The code for existing major modes follows various coding conventions, including conventions for local keymap and syntax table initialization, global names, and hooks. Please follow these conventions when you define a new major mode: * Define a command whose name ends in `-mode', with no arguments, that switches to the new mode in the current buffer. This command should set up the keymap, syntax table, and local variables in an existing buffer without changing the buffer's text. * Write a documentation string for this command that describes the special commands available in this mode. `C-h m' (`describe-mode') in your mode will display this string. The documentation string may include the special documentation substrings, `\[COMMAND]', `\{KEYMAP}', and `\<KEYMAP>', that enable the documentation to adapt automatically to the user's own key bindings. *Note Keys in Documentation::. * The major mode command should start by calling `kill-all-local-variables'. This is what gets rid of the local variables of the major mode previously in effect. * The major mode command should set the variable `major-mode' to the major mode command symbol. This is how `describe-mode' discovers which documentation to print. * The major mode command should set the variable `mode-name' to the "pretty" name of the mode, as a string. This appears in the mode line. * Since all global names are in the same name space, all the global variables, constants, and functions that are part of the mode should have names that start with the major mode name (or with an abbreviation of it if the name is long). *Note Style Tips::. * The major mode should usually have its own keymap, which is used as the local keymap in all buffers in that mode. The major mode function should call `use-local-map' to install this local map. *Note Active Keymaps::, for more information. This keymap should be kept in a global variable named `MODENAME-mode-map'. Normally the library that defines the mode sets this variable. * The mode may have its own syntax table or may share one with other related modes. If it has its own syntax table, it should store this in a variable named `MODENAME-mode-syntax-table'. *Note Syntax Tables::. * The mode may have its own abbrev table or may share one with other related modes. If it has its own abbrev table, it should store this in a variable named `MODENAME-mode-abbrev-table'. *Note Abbrev Tables::. * Use `defvar' to set mode-related variables, so that they are not reinitialized if they already have a value. (Such reinitialization could discard customizations made by the user.) * To make a buffer-local binding for an Emacs customization variable, use `make-local-variable' in the major mode command, not `make-variable-buffer-local'. The latter function would make the variable local to every buffer in which it is subsequently set, which would affect buffers that do not use this mode. It is undesirable for a mode to have such global effects. *Note Buffer-Local Variables::. It's ok to use `make-variable-buffer-local', if you wish, for a variable used only within a single Lisp package. * Each major mode should have a "mode hook" named `MODENAME-mode-hook'. The major mode command should run that hook, with `run-hooks', as the very last thing it does. *Note Hooks::. * The major mode command may also run the hooks of some more basic modes. For example, `indented-text-mode' runs `text-mode-hook' as well as `indented-text-mode-hook'. It may run these other hooks immediately before the mode's own hook (that is, after everything else), or it may run them earlier. * If something special should be done if the user switches a buffer from this mode to any other major mode, the mode can set a local value for `change-major-mode-hook'. * If this mode is appropriate only for specially-prepared text, then the major mode command symbol should have a property named `mode-class' with value `special', put on as follows: (put 'funny-mode 'mode-class 'special) This tells XEmacs that new buffers created while the current buffer has Funny mode should not inherit Funny mode. Modes such as Dired, Rmail, and Buffer List use this feature. * If you want to make the new mode the default for files with certain recognizable names, add an element to `auto-mode-alist' to select the mode for those file names. If you define the mode command to autoload, you should add this element in the same file that calls `autoload'. Otherwise, it is sufficient to add the element in the file that contains the mode definition. *Note Auto Major Mode::. * In the documentation, you should provide a sample `autoload' form and an example of how to add to `auto-mode-alist', that users can include in their `.emacs' files. * The top-level forms in the file defining the mode should be written so that they may be evaluated more than once without adverse consequences. Even if you never load the file more than once, someone else will. - Variable: change-major-mode-hook This normal hook is run by `kill-all-local-variables' before it does anything else. This gives major modes a way to arrange for something special to be done if the user switches to a different major mode. For best results, make this variable buffer-local, so that it will disappear after doing its job and will not interfere with the subsequent major mode. *Note Hooks::. File: lispref.info, Node: Example Major Modes, Next: Auto Major Mode, Prev: Major Mode Conventions, Up: Major Modes Major Mode Examples ------------------- Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts from `text-mode.el' that illustrate many of the conventions listed above: ;; Create mode-specific tables. (defvar text-mode-syntax-table nil "Syntax table used while in text mode.") (if text-mode-syntax-table () ; Do not change the table if it is already set up. (setq text-mode-syntax-table (make-syntax-table)) (modify-syntax-entry ?\" ". " text-mode-syntax-table) (modify-syntax-entry ?\\ ". " text-mode-syntax-table) (modify-syntax-entry ?' "w " text-mode-syntax-table)) (defvar text-mode-abbrev-table nil "Abbrev table used while in text mode.") (define-abbrev-table 'text-mode-abbrev-table ()) (defvar text-mode-map nil) ; Create a mode-specific keymap. (if text-mode-map () ; Do not change the keymap if it is already set up. (setq text-mode-map (make-sparse-keymap)) (define-key text-mode-map "\t" 'tab-to-tab-stop) (define-key text-mode-map "\es" 'center-line) (define-key text-mode-map "\eS" 'center-paragraph)) Here is the complete major mode function definition for Text mode: (defun text-mode () "Major mode for editing text intended for humans to read. Special commands: \\{text-mode-map} Turning on text-mode runs the hook `text-mode-hook'." (interactive) (kill-all-local-variables) (use-local-map text-mode-map) ; This provides the local keymap. (setq mode-name "Text") ; This name goes into the modeline. (setq major-mode 'text-mode) ; This is how `describe-mode' ; finds the doc string to print. (setq local-abbrev-table text-mode-abbrev-table) (set-syntax-table text-mode-syntax-table) (run-hooks 'text-mode-hook)) ; Finally, this permits the user to ; customize the mode with a hook. The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) have more features than Text mode and the code is correspondingly more complicated. Here are excerpts from `lisp-mode.el' that illustrate how these modes are written. ;; Create mode-specific table variables. (defvar lisp-mode-syntax-table nil "") (defvar emacs-lisp-mode-syntax-table nil "") (defvar lisp-mode-abbrev-table nil "") (if (not emacs-lisp-mode-syntax-table) ; Do not change the table ; if it is already set. (let ((i 0)) (setq emacs-lisp-mode-syntax-table (make-syntax-table)) ;; Set syntax of chars up to 0 to class of chars that are ;; part of symbol names but not words. ;; (The number 0 is `48' in the ASCII character set.) (while (< i ?0) (modify-syntax-entry i "_ " emacs-lisp-mode-syntax-table) (setq i (1+ i))) ... ;; Set the syntax for other characters. (modify-syntax-entry ? " " emacs-lisp-mode-syntax-table) (modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table) ... (modify-syntax-entry ?$ "() " emacs-lisp-mode-syntax-table) (modify-syntax-entry ?$ ")( " emacs-lisp-mode-syntax-table) ...)) ;; Create an abbrev table for lisp-mode. (define-abbrev-table 'lisp-mode-abbrev-table ()) Much code is shared among the three Lisp modes. The following function sets various variables; it is called by each of the major Lisp mode functions: (defun lisp-mode-variables (lisp-syntax) ;; The `lisp-syntax' argument is `nil' in Emacs Lisp mode, ;; and `t' in the other two Lisp modes. (cond (lisp-syntax (if (not lisp-mode-syntax-table) ;; The Emacs Lisp mode syntax table always exists, but ;; the Lisp Mode syntax table is created the first time a ;; mode that needs it is called. This is to save space. (progn (setq lisp-mode-syntax-table (copy-syntax-table emacs-lisp-mode-syntax-table)) ;; Change some entries for Lisp mode. (modify-syntax-entry ?\| "\" " lisp-mode-syntax-table) (modify-syntax-entry ?\[ "_ " lisp-mode-syntax-table) (modify-syntax-entry ?\] "_ " lisp-mode-syntax-table))) (set-syntax-table lisp-mode-syntax-table))) (setq local-abbrev-table lisp-mode-abbrev-table) ...) Functions such as `forward-paragraph' use the value of the `paragraph-start' variable. Since Lisp code is different from ordinary text, the `paragraph-start' variable needs to be set specially to handle Lisp. Also, comments are indented in a special fashion in Lisp and the Lisp modes need their own mode-specific `comment-indent-function'. The code to set these variables is the rest of `lisp-mode-variables'. (make-local-variable 'paragraph-start) ;; Having `^' is not clean, but `page-delimiter' ;; has them too, and removing those is a pain. (setq paragraph-start (concat "^$\\|" page-delimiter)) ... (make-local-variable 'comment-indent-function) (setq comment-indent-function 'lisp-comment-indent)) Each of the different Lisp modes has a slightly different keymap. For example, Lisp mode binds `C-c C-l' to `run-lisp', but the other Lisp modes do not. However, all Lisp modes have some commands in common. The following function adds these common commands to a given keymap. (defun lisp-mode-commands (map) (define-key map "\e\C-q" 'indent-sexp) (define-key map "\177" 'backward-delete-char-untabify) (define-key map "\t" 'lisp-indent-line)) Here is an example of using `lisp-mode-commands' to initialize a keymap, as part of the code for Emacs Lisp mode. First we declare a variable with `defvar' to hold the mode-specific keymap. When this `defvar' executes, it sets the variable to `nil' if it was void. Then we set up the keymap if the variable is `nil'. This code avoids changing the keymap or the variable if it is already set up. This lets the user customize the keymap. (defvar emacs-lisp-mode-map () "") (if emacs-lisp-mode-map () (setq emacs-lisp-mode-map (make-sparse-keymap)) (define-key emacs-lisp-mode-map "\e\C-x" 'eval-defun) (lisp-mode-commands emacs-lisp-mode-map)) Finally, here is the complete major mode function definition for Emacs Lisp mode. (defun emacs-lisp-mode () "Major mode for editing Lisp code to run in XEmacs. Commands: Delete converts tabs to spaces as it moves back. Blank lines separate paragraphs. Semicolons start comments. \\{emacs-lisp-mode-map} Entry to this mode runs the hook `emacs-lisp-mode-hook'." (interactive) (kill-all-local-variables) (use-local-map emacs-lisp-mode-map) ; This provides the local keymap. (set-syntax-table emacs-lisp-mode-syntax-table) (setq major-mode 'emacs-lisp-mode) ; This is how `describe-mode' ; finds out what to describe. (setq mode-name "Emacs-Lisp") ; This goes into the modeline. (lisp-mode-variables nil) ; This defines various variables. (run-hooks 'emacs-lisp-mode-hook)) ; This permits the user to use a ; hook to customize the mode. 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 specifes 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'.