This is Info file elisp, produced by Makeinfo version 1.68 from the input file elisp.texi. INFO-DIR-SECTION Editors START-INFO-DIR-ENTRY * Elisp: (elisp). The Emacs Lisp Reference Manual. END-INFO-DIR-ENTRY This version is the edition 2.5 of the GNU Emacs Lisp Reference Manual. It corresponds to Emacs Version 20.3 Published by the Free Software Foundation 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998 Free Software Foundation, Inc. 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: elisp, 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" 'indent-relative) (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) (setq local-abbrev-table text-mode-abbrev-table) (set-syntax-table text-mode-syntax-table) (make-local-variable 'paragraph-start) (setq paragraph-start (concat "[ \t]*$\\|" page-delimiter)) (make-local-variable 'paragraph-separate) (setq paragraph-separate paragraph-start) (setq mode-name "Text") (setq major-mode 'text-mode) (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) (cond (lisp-syntax (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) (setq paragraph-start (concat page-delimiter "\\|$" )) (make-local-variable 'paragraph-separate) (setq paragraph-separate paragraph-start) ... (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-z' to `run-lisp', but the other Lisp modes do not. However, all Lisp modes have some commands in common. The following code sets up the common commands: (defvar shared-lisp-mode-map () "Keymap for commands shared by all sorts of Lisp modes.") (if shared-lisp-mode-map () (setq shared-lisp-mode-map (make-sparse-keymap)) (define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp) (define-key shared-lisp-mode-map "\177" 'backward-delete-char-untabify)) And here is the code to set up the keymap for Lisp mode: (defvar lisp-mode-map () "Keymap for ordinary Lisp mode....") (if lisp-mode-map () (setq lisp-mode-map (make-sparse-keymap)) (set-keymap-parent lisp-mode-map shared-lisp-mode-map) (define-key lisp-mode-map "\e\C-x" 'lisp-eval-defun) (define-key lisp-mode-map "\C-c\C-z" 'run-lisp)) Finally, here is the complete major mode function definition for Emacs Lisp mode. (defun lisp-mode () "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp. Commands: Delete converts tabs to spaces as it moves back. Blank lines separate paragraphs. Semicolons start comments. \\{lisp-mode-map} Note that `run-lisp' may be used either to start an inferior Lisp job or to switch back to an existing one. Entry to this mode calls the value of `lisp-mode-hook' if that value is non-nil." (interactive) (kill-all-local-variables) (use-local-map lisp-mode-map) ; Select the mode's keymap. (setq major-mode 'lisp-mode) ; This is how `describe-mode' ; finds out what to describe. (setq mode-name "Lisp") ; This goes into the mode line. (lisp-mode-variables t) ; This defines various variables. (setq imenu-case-fold-search t) (set-syntax-table lisp-mode-syntax-table) (run-hooks 'lisp-mode-hook)) ; This permits the user to use a ; hook to customize the mode.  File: elisp, Node: Auto Major Mode, Next: Mode Help, Prev: Example Major Modes, Up: Major Modes How Emacs Chooses a Major Mode ------------------------------ Based on information in the file name or in the file itself, Emacs automatically selects a major mode for the new buffer when a file is visited. It also processes local variables specified in the file text. - 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 buffer-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, the file's 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. *Note Local Variables in Files: (emacs)File variables, for the syntax of the local variables section of a file. If you run `normal-mode' interactively, the argument FIND-FILE is normally `nil'. In this case, `normal-mode' unconditionally processes any local variables list. `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 file's 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'), on the `#!' line (using `interpreter-mode-alist'), or on the file's local variables list. 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', Emacs uses the (previously) current buffer's major mode for the major mode of a new buffer. However, if that 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. 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 commands. 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 Emacs 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, Emacs searches `auto-mode-alist' again for a match against the portion of the file name that did not match before. This feature is useful for uncompression packages: an entry of the form `("\\.gz\\'" FUNCTION t)' 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 (within directory) 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 an interpreter which matches INTERPRETER. The value of INTERPRETER is actually a regular expression. 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 specified by the contents of 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: elisp, 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: elisp, 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: elisp, Node: Minor Modes, Next: Mode Line 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 would be unwieldy. A minor mode is not usually a modification of single major mode. For example, Auto Fill mode works with 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 Emacs. 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. * Easy-Mmode:: A convenient facility for defining minor modes.  File: elisp, 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 control the minor mode. We call this the "mode variable". The minor mode command should set this variable (`nil' to disable; anything else to enable). If it is possible, implement the mode so that setting the variable automatically enables or disables the mode. Then the minor mode command does not need to do anything except set the variable. This variable is used in conjunction with the `minor-mode-alist' to display the minor mode name in the mode line. 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 Mode Line Variables::.), if you want to indicate the minor mode in the mode line. 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 mode line. 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))) You can also use `add-to-list' to add an element to this list just once (*note Setting Variables::.).  File: elisp, Node: Keymaps and Minor Modes, Next: Easy-Mmode, 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.) The key sequences bound in a minor mode should consist of `C-c' followed by a punctuation character *other than* `{', `}', `<', `>', `:' or `;'. (Those few punctuation characters are reserved for major modes.)  File: elisp, Node: Easy-Mmode, Prev: Keymaps and Minor Modes, Up: Minor Modes Easy-Mmode ---------- The easy-mmode package provides a convenient way of implementing a minor mode; with it, you can specify all about a simple minor mode in one self-contained definition. - Macro: easy-mmode-define-minor-mode MODE DOC &optional INIT-VALUE MODE-INDICATOR KEYMAP This macro defines a new minor mode whose name is MODE (a symbol). This macro defines a command named MODE which toggles the minor mode, and has DOC as its documentation string. It also defines a variable named MODE, which is set to `t' or `nil' by enabling or disabling the mode. The variable is initialized to INIT-VALUE. The string MODE-INDICATOR says what to display in the mode line when the mode is enabled; if it is `nil', the mode is not displayed in the mode line. The optional argument KEYMAP specifies the keymap for the minor mode. It can be a variable name, whose value is the keymap, or it can be an alist specifying bindings in this form: (KEY-SEQUENCE . DEFINITION) Here is an example of using `easy-mmode-define-minor-mode': (easy-mmode-define-minor-mode hungry-mode "Toggle Hungry mode. With no argument, this command toggles the mode. Non-null prefix argument turns on the mode. Null prefix argument turns off the mode. When Hungry mode is enabled, the control delete key gobbles all preceding whitespace except the last. See the command \\[hungry-electric-delete]." ;; The initial value. nil ;; The indicator for the mode line. " Hungry" ;; The minor mode bindings. '(("\C-\^?" . hungry-electric-delete) ("\C-\M-\^?" . (lambda () (interactive) (hungry-electric-delete t))))) This defines a minor mode named "Hungry mode", a command named `hungry-mode' to toggle it, a variable named `hungry-mode' which indicates whether the mode is enabled, and a variable named `hungry-mode-map' which holds the keymap that is active when the mode is enabled. It initializes the keymap with key bindings for `C-' and `C-M-'.  File: elisp, Node: Mode Line Format, Next: Imenu, Prev: Minor Modes, Up: Modes Mode Line Format ================ Each Emacs window (aside from minibuffer windows) includes a mode line, which displays status information about the buffer displayed in the window. The mode line 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 mode line are controlled. We include it in this chapter because much of the information displayed in the mode line relates to the enabled major and minor modes. `mode-line-format' is a buffer-local variable that holds a template used to display the mode line of the current buffer. All windows for the same buffer use the same `mode-line-format' and their mode lines appear the same (except for scrolling percentages, and line and column numbers). The mode line 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 `mode-line-format' (*note Mode Line Variables::.), or any other variables and data structures that affect how text is displayed (*note Display::.), you may want to force an update of the mode line so as to display the new information or display it in the new way. - Function: force-mode-line-update Force redisplay of the current buffer's mode line. The mode line is usually displayed in inverse video; see `mode-line-inverse-video' in *Note Inverse Video::. * Menu: * Mode Line Data:: The data structure that controls the mode line. * Mode Line Variables:: Variables used in that data structure. * %-Constructs:: Putting information into a mode line.  File: elisp, Node: Mode Line Data, Next: Mode Line Variables, Up: Mode Line Format The Data Structure of the Mode Line ----------------------------------- The mode line 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 "mode line construct", and it is built in recursive fashion out of simpler mode line constructs. The same data structure is used for constructing frame titles (*note Frame Titles::.). - Variable: mode-line-format The value of this variable is a mode line construct with overall responsibility for the mode line format. The value of this variable controls which other variables are used to form the mode line text, and where they appear. A mode line 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 mode line constructs as their values. The default value of `mode-line-format' incorporates the values of variables such as `mode-name' and `minor-mode-alist'. Because of this, very few modes need to alter `mode-line-format' itself. For most purposes, it is sufficient to alter some of the variables that `mode-line-format' refers to. A mode line 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 mode line 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 mode line construct stands for its value. The value of SYMBOL is used as a mode line 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 mode line 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 mode line 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 `mode-line-format' itself, the new value should use the same variables that appear in the default value (*note Mode Line 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 `mode-line-format' that might be useful for `shell-mode', since it contains the host name and default directory. (setq mode-line-format (list "-" 'mode-line-mule-info 'mode-line-modified 'mode-line-frame-identification "%b--" ;; Note that this is evaluated while making the list. ;; It makes a mode line construct which is just a string. (getenv "HOST") ":" 'default-directory " " 'global-mode-string " %[(" 'mode-name 'mode-line-process 'minor-mode-alist "%n" ")%]--" '(which-func-mode ("" which-func-format "--")) '(line-number-mode "L%l--") '(column-number-mode "C%c--") '(-3 . "%p") "-%-")) (The variables `line-number-mode', `column-number-mode' and `which-func-mode' enable particular minor modes; as usual, these variable names are also the minor mode command names.)  File: elisp, Node: Mode Line Variables, Next: %-Constructs, Prev: Mode Line Data, Up: Mode Line Format Variables Used in the Mode Line ------------------------------- This section describes variables incorporated by the standard value of `mode-line-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 mode line if `mode-line-format' were changed to use them. - Variable: mode-line-mule-info This variable holds the value of the mode-line construct that displays information about the language environment, buffer coding system, and current input method. *Note Non-ASCII Characters::. - Variable: mode-line-modified This variable holds the value of the mode-line construct that displays whether the current buffer is modified. The default value of `mode-line-modified' is `("%1*%1+")'. This means that the mode line 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 mode line. - Variable: mode-line-frame-identification This variable identifies the current frame. The default value is `" "' if you are using a window system which can show multiple frames, or `"-%F "' on an ordinary terminal which shows only one frame at a time. - Variable: mode-line-buffer-identification This variable identifies the buffer being displayed in the window. Its default value is `("%12b")', which displays the buffer name, padded with spaces to at least 12 columns. - Variable: global-mode-string This variable holds a mode line 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 that is obsolete, since the variable is included in the mode line from `mode-line-format'. - 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 mode line. - Variable: minor-mode-alist This variable holds an association list whose elements specify how the mode line should indicate that a minor mode is active. Each element of the `minor-mode-alist' should be a two-element list: (MINOR-MODE-VARIABLE MODE-LINE-STRING) More generally, MODE-LINE-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' itself is not buffer-local. Each variable mentioned in the alist should be buffer-local if its minor mode can be enabled separately in each buffer. - Variable: mode-line-process This buffer-local variable contains the mode line 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-mode-line-format This variable holds the default `mode-line-format' for buffers that do not override it. This is the same as `(default-value 'mode-line-format)'. The default value of `default-mode-line-format' is this list: ("-" mode-line-mule-info mode-line-modified mode-line-frame-identification mode-line-buffer-identification " " global-mode-string " %[(" mode-name mode-line-process minor-mode-alist "%n" ")%]--" (which-func-mode ("" which-func-format "--")) (line-number-mode "L%l--") (column-number-mode "C%c--") (-3 . "%p") "-%-") - Variable: vc-mode The variable `vc-mode', buffer-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: elisp, Node: %-Constructs, Prev: Mode Line Variables, Up: Mode Line Format `%'-Constructs in the Mode Line ------------------------------- 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 title (only on a window system) or the name of the selected frame. *Note Window Frame Parameters::. `%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::. `%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 mode line. 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: elisp, Node: Imenu, Next: Font Lock Mode, Prev: Mode Line Format, Up: Modes Imenu ===== "Imenu" is a feature that lets users select a definition or section in the buffer, from a menu which lists all of them, to go directly to that location in the buffer. Imenu works by constructing a buffer index which lists the names and positions of the definitions or portions of in the buffer, so the user can pick one of them to move to. This section explains how to customize Imenu for a major mode. The usual and simplest way is to set the variable `imenu-generic-expression': - Variable: imenu-generic-expression This variable, if non-`nil', specifies regular expressions for finding definitions for Imenu. In the simplest case, elements should look like this: (MENU-TITLE REGEXP SUBEXP) Here, if MENU-TITLE is non-`nil', it says that the matches for this element should go in a submenu of the buffer index; MENU-TITLE itself specifies the name for the submenu. If MENU-TITLE is `nil', the matches for this element go directly in the top level of the buffer index. The second item in the list, REGEXP, is a regular expression (*note Regular Expressions::.); wherever it matches, that is a definition to mention in the buffer index. The third item, SUBEXP, indicates which subexpression in REGEXP matches the definition's name. An element can also look like this: (MENU-TITLE REGEXP INDEX FUNCTION ARGUMENTS...) Each match for this element creates a special index item which, if selected by the user, calls FUNCTION with arguments ITEM-NAME, the buffer position, and ARGUMENTS. For Emacs Lisp mode, PATTERN could look like this: ((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2) ("*Vars*" "^\\s-*(def\\(var\\|const\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2) ("*Types*" "^\\s-*\ (def\\(type\\|struct\\|class\\|ine-condition\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2)) Setting this variable makes it buffer-local in the current buffer. - Variable: imenu-case-fold-search This variable controls whether matching against IMENU-GENERIC-EXPRESSION is case-sensitive: `t', the default, means matching should ignore case. Setting this variable makes it buffer-local in the current buffer. - Variable: imenu-syntax-alist This variable is an alist of syntax table modifiers to use while processing `imenu-generic-expression', to override the syntax table of the current buffer. Each element should have this form: (CHARACTERS . SYNTAX-DESCRIPTION) The CAR, CHARACTERS, can be either a character or a string. The element says to give that character or characters the syntax specified by SYNTAX-DESCRIPTION, which is passed to `modify-syntax-entry' (*note Syntax Table Functions::.). This feature is typically used to give word syntax to characters which normally have symbol syntax, and thus to simplify `imenu-generic-expression' and speed up matching. For example, Fortran mode uses it this way: (setq imenu-syntax-alist '(("_$" . "w"))) The `imenu-generic-expression' patterns can then use `\\sw+' instead of `\\(\\sw\\|\\s_\\)+'. Note that this technique may be inconvenient to use when the mode needs to limit the initial character of a name to a smaller set of characters than are allowed in the rest of a name. Setting this variable makes it buffer-local in the current buffer. Another way to customize Imenu for a major mode is to set the variables `imenu-prev-index-position-function' and `imenu-extract-index-name-function': - Variable: imenu-prev-index-position-function If this variable is non-`nil', its value should be a function for finding the next definition to mention in the buffer index, moving backwards in the file. The function should leave point at the place to be connected to the index item; it should return `nil' if it doesn't find another item. Setting this variable makes it buffer-local in the current buffer. - Variable: imenu-extract-index-name-function If this variable is non-`nil', its value should be a function to return the name for a definition, assuming point is in that definition as the `imenu-prev-index-position-function' function would leave it. Setting this variable makes it buffer-local in the current buffer. The last way to customize Imenu for a major mode is to set the variables `imenu-create-index-function': - Variable: imenu-create-index-function This variable specifies the function to use for creating a buffer index. The function should take no arguments, and return an index for the current buffer. It is called within `save-excursion', so where it leaves point makes no difference. The default value is a function that uses `imenu-generic-expression' to produce the index alist. If you specify a different function, then `imenu-generic-expression' is not used. Setting this variable makes it buffer-local in the current buffer. - Variable: imenu-index-alist This variable holds the index alist for the current buffer. Setting it makes it buffer-local in the current buffer. Simple elements in the alist look like `(INDEX-NAME . INDEX-POSITION)'. Selecting a simple element has the effect of moving to position INDEX-POSITION in the buffer. Special elements look like `(INDEX-NAME POSITION FUNCTION ARGUMENTS...)'. Selecting a special element performs (funcall FUNCTION INDEX-NAME POSITION ARGUMENTS...) A nested sub-alist element looks like `(INDEX-NAME SUB-ALIST)'.  File: elisp, Node: Font Lock Mode, Next: Hooks, Prev: Imenu, Up: Modes Font Lock Mode ============== "Font Lock mode" is a feature that automatically attaches `face' properties to certain parts of the buffer based on their syntactic role. How it parses the buffer depends on the major mode; most major modes define syntactic criteria for which faces to use, in which contexts. This section explains how to customize Font Lock for a particular language--in other words, for a particular major mode. Font Lock mode finds text to highlight in two ways: through syntactic parsing based on the syntax table, and through searching (usually for regular expressions). Syntactic fontification happens first; it finds comments and string constants, and highlights them using `font-lock-comment-face' and `font-lock-string-face' (*note Faces for Font Lock::.); search-based fontification follows. * Menu: * Font Lock Basics:: * Search-based Fontification:: * Other Font Lock Variables:: * Levels of Font Lock:: * Faces for Font Lock:: * Syntactic Font Lock::  File: elisp, Node: Font Lock Basics, Next: Search-based Fontification, Up: Font Lock Mode Font Lock Basics ---------------- There are several variables that control how Font Lock mode highlights text. But major modes should not set any of these variables directly. Instead, it should set `font-lock-defaults' as a buffer-local variable. The value assigned to this variable is used, if and when Font Lock mode is enabled, to set all the other variables. - Variable: font-lock-defaults This variable is set by major modes, as a buffer-local variable, to specify how to fontify text in that mode. The value should look like this: (KEYWORDS KEYWORDS-ONLY CASE-FOLD SYNTAX-ALIST SYNTAX-BEGIN OTHER-VARS...) The first element, KEYWORDS, indirectly specifies the value of `font-lock-keywords'. It can be a symbol, a variable whose value is list to use for `font-lock-keywords'. It can also be a list of several such symbols, one for each possible level of fontification. The first symbol specifies how to do level 1 fontification, the second symbol how to do level 2, and so on. The second element, KEYWORDS-ONLY, specifies the value of the variable `font-lock-keywords-only'. If this is non-`nil', syntactic fontification (of strings and comments) is not performed. The third element, CASE-FOLD, specifies the value of `font-lock-case-fold-search'. If it is non-`nil', Font Lock mode ignores case when searching as directed by `font-lock-keywords'. If the fourth element, SYNTAX-ALIST, is non-`nil', it should be a list of cons cells of the form `(CHAR-OR-STRING . STRING)'. These are used to set up a syntax table for fontification (*note Syntax Table Functions::.). The resulting syntax table is stored in `font-lock-syntax-table'. The fifth element, SYNTAX-BEGIN, specifies the value of `font-lock-beginning-of-syntax-function' (see below). Any further elements OTHER-VARS are have form `(VARIABLE . VALUE)'. This kind of element means to make VARIABLE buffer-local and then set it to VALUE. This is used to set other variables that affect fontification.