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This is Info file elisp, produced by Makeinfo-1.55 from the input file elisp.texi. This is edition 2.0 of the GNU Emacs Lisp Reference Manual, for Emacs Version 19. Published by the Free Software Foundation, 675 Massachusetts Avenue, Cambridge, MA 02139 USA Copyright (C) 1990, 1991, 1992, 1993 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. File: elisp, Node: The Kill Ring, Next: Undo, Prev: User-Level Deletion, Up: Text The Kill Ring ============= "Kill" functions delete text like the deletion functions, but save it so that the user can reinsert it by "yanking". Most of these functions have `kill-' in their name. By contrast, the functions whose names start with `delete-' normally do not save text for yanking (though they can still be undone); these are "deletion" functions. Most of the kill commands are primarily for interactive use, and are not described here. What we do describe are the functions provided for use in writing such commands. When deleting text for internal purposes within a Lisp function, you should normally use deletion functions, so as not to disturb the kill ring contents. *Note Deletion::. Emacs saves the last several batches of killed text in a list. We call it the "kill ring" because, in yanking, the elements are considered to be in a cyclic order. The list is kept in the variable `kill-ring', and can be operated on with the usual functions for lists; there are also specialized functions, described in this section, which treat it as a ring. Some people think use of the word "kill" in Emacs is unfortunate, since it refers to processes which specifically *do not* destroy the entities "killed". This is in sharp contrast to ordinary life, in which death is permanent and "killed" entities do not come back to life. Therefore, other metaphors have been proposed. For example, the term "cut ring" makes sense to people who, in pre-computer days, used scissors and paste to cut up and rearrange manuscripts. However, it would be difficult to change now. * Menu: * Kill Ring Concepts:: What text looks like in the kill ring. * Kill Functions:: Functions that kill text. * Yank Commands:: Commands that access the kill ring. * Low Level Kill Ring:: Functions and variables for kill ring access. * Internals of Kill Ring:: Variables that hold kill-ring data. File: elisp, Node: Kill Ring Concepts, Next: Kill Functions, Up: The Kill Ring Kill Ring Concepts ------------------ The kill ring records killed text as strings in a list. A short kill ring, for example, might look like this: ("some text" "a different piece of text" "yet more text") New entries in the kill ring go at the front of the list. When the list reaches `kill-ring-max' entries in length, adding a new entry automatically deletes the last entry. When kill commands are interwoven with other commands, the killed portions of text are put into separate entries in the kill ring. But when two or more kill commands are executed in succession, the text they kill forms a single entry, because the second and subsequent consecutive kill commands append to the entry made by the first one. The user can reinsert or "yank" text from any element in the kill ring. One of the entries in the ring is considered the "front", and the simplest yank command yanks that entry. Other yank commands "rotate" the ring by designating other entries as the "front". File: elisp, Node: Kill Functions, Next: Yank Commands, Prev: Kill Ring Concepts, Up: The Kill Ring Functions for Killing --------------------- `kill-region' is the usual subroutine for killing text. Any command that calls this function is a "kill command" (and should probably have `kill' in its name). `kill-region' puts the newly killed text in a new element at the beginning of the kill ring or adds it to the most recent element. It uses the `last-command' variable to keep track of whether the previous was a kill command, and in such cases appends the killed text to the most recent entry. - Command: kill-region START END This function kills the text in the region defined by START and END. The text is deleted but saved in the kill ring. The value is always `nil'. In an interactive call, START and END are point and the mark. If the buffer is read-only, `kill-region' modifies the kill ring just the same, then signals an error without modifying the buffer. This is convenient because it lets the user use all the kill commands to copy text into the kill ring from a read-only buffer. - Command: copy-region-as-kill START END This function saves the region defined by START and END on the kill ring, but does not delete the text from the buffer. It returns `nil'. It also indicates the extent of the text copied by moving the cursor momentarily, or by displaying a message in the echo area. Don't use this command in Lisp programs; use `kill-new' or `kill-append' instead. *Note Low Level Kill Ring::. In an interactive call, START and END are point and the mark. File: elisp, Node: Yank Commands, Next: Low Level Kill Ring, Prev: Kill Functions, Up: The Kill Ring Functions for Yanking --------------------- - Command: yank &optional ARG This function inserts the text in the first entry in the kill ring directly before point. After the yank, the mark is positioned at the beginning and point is positioned after the end of the inserted text. If ARG is a list (which occurs interactively when the user types `C-u' with no digits), then `yank' inserts the text as described above, but puts point before the yanked text and puts the mark after it. If ARG is a number, then `yank' inserts the ARGth most recently killed text. `yank' does not alter the contents of the kill ring or rotate it. It returns `nil'. - Command: yank-pop ARG This function replaces the just-yanked text with another batch of killed text--another element of the kill ring. This command is allowed only immediately after a `yank' or a `yank-pop'. At such a time, the region contains text that was just inserted by the previous `yank'. `yank-pop' deletes that text and inserts in its place a different stretch of killed text. The text that is deleted is not inserted into the kill ring, since it is already in the kill ring somewhere. If ARG is `nil', then the existing region contents are replaced with the previous element of the kill ring. If ARG is numeric, then the ARGth previous kill is the replacement. If ARG is negative, a more recent kill is the replacement. The sequence of kills in the kill ring wraps around, so that after the oldest one comes the newest one, and before the newest one goes the oldest. The value is always `nil'. File: elisp, Node: Low Level Kill Ring, Next: Internals of Kill Ring, Prev: Yank Commands, Up: The Kill Ring Low Level Kill Ring ------------------- These functions and variables provide access to the kill ring at a lower level, but still convenient for use in Lisp programs. They take care of interaction with X Window selections. They do not exist in Emacs version 18. - Function: current-kill N &optional DO-NOT-MOVE The function `current-kill' rotates the yanking pointer in the kill ring by N places, and returns the text at that place in the ring. If the optional second argument DO-NOT-MOVE is non-`nil', then `current-kill' doesn't alter the yanking pointer; it just returns the Nth kill forward from the current yanking pointer. If N is zero, indicating a request for the latest kill, `current-kill' calls the value of `interprogram-paste-function' (documented below) before consulting the kill ring. - Function: kill-new STRING This function puts the text STRING into the kill ring as a new entry at the front of the ring. It also discards the oldest entry if appropriate. It also invokes the value of `interprogram-cut-function' (see below). - Function: kill-append STRING BEFORE-P This function appends the text STRING to the first entry in the kill ring. Normally STRING goes at the end of the entry, but if BEFORE-P is non-`nil', it goes at the beginning. This function also invokes the value of `interprogram-cut-function' (see below). - Variable: interprogram-paste-function This variable provides a way of transferring killed text from other programs, when you are using a window system. Its value should be `nil' or a function of no arguments. If the value is a function, it is called when the "most recent kill" value is called for. If the function returns a non-`nil' values, then that value is used as the "most recent kill". If it returns `nil', then the first element of the kill ring is used. - Variable: interprogram-cut-function This variable provides a way of communicating killed text to and from other programs, when you are using a window system. Its value should be `nil' or a function of one argument. If the value is a function, it is called whenever the "most recent kill" is changed, with the new string of killed text as an argument. File: elisp, Node: Internals of Kill Ring, Prev: Low Level Kill Ring, Up: The Kill Ring Internals of the Kill Ring -------------------------- The variable `kill-ring' holds the kill ring contents, in the form of a list of strings. The most recent kill is always at the front of the list. The `kill-ring-yank-pointer' variable points to a link in the kill ring list, whose CAR is the text that "yank" functions should copy. Moving `kill-ring-yank-pointer' to a different link is called "rotating the kill ring". We call the kill ring a "ring" because the functions that move the yank pointer wrap around from the end of the list to the beginning, or vice-versa. Rotating the ring does not change the value of `kill-ring'. Both `kill-ring' and `kill-ring-yank-pointer' are Lisp variables whose values are normally lists. The word "pointer" in the name of the `kill-ring-yank-pointer' indicates that the variable's purpose is to identify one element of the list for use by the next yank command. The value of `kill-ring-yank-pointer' is always `eq' to one of the links in the kill ring list. The element it identifies is the CAR of that link. Commands which change the text in the kill ring also set this variable from `kill-ring'. The effect is to rotate the ring so that the newly killed text is at front. Here is a diagram that shows the variable `kill-ring-yank-pointer' pointing to the second entry in the kill ring `("some text" "a different piece of text" "yet more text")'. kill-ring kill-ring-yank-pointer | | | ___ ___ ---> ___ ___ ___ ___ --> |___|___|------> |___|___|--> |___|___|--> nil | | | | | | | | -->"yet more text" | | | --> "a different piece of text" | --> "some text" This circumstance might occur after `C-y' (`yank') immediately followed by `M-y' (`yank-pop'). - Variable: kill-ring List of killed text sequences, most recently killed first. - Variable: kill-ring-yank-pointer This variable's value indicates which element of the kill ring is at the "front" of the ring for yanking. More precisely, the value is a sublist of the value of `kill-ring', and its CAR is the kill string that `C-y' should yank. - User Option: kill-ring-max The value of this variable is the maximum length to which the kill ring can grow, before elements are thrown away at the end. The default value for `kill-ring-max' is 30. File: elisp, Node: Undo, Next: Maintaining Undo, Prev: The Kill Ring, Up: Text Undo ==== Most buffers have an "undo list" which records all changes made to the buffer's text so that they can be undone. (The buffers which don't have one are usually special-purpose buffers for which Emacs assumes that undoing is not useful.) All the primitives which modify the text in the buffer automatically add elements to the front of the undo list, which you can find in the variable `buffer-undo-list'. - Variable: buffer-undo-list This variable's value is the undo list of the current buffer. A value of `t' disables the recording of undo information. Here are the kinds of elements an undo list can have: `INTEGER' This kind of element records a previous value of point. Ordinary cursor motion does not get any sort of undo record, but these entries are used to record where point was before a deletion. `(BEG . END)' This kind of element indicates how to delete text that was inserted. Upon insertion, the text occupied the range BEG-END in the buffer. `(POS . DELETED)' This kind of element indicates how to reinsert text that was deleted. The deleted text itself is the string DELETED. The place to reinsert it is POS. `(t HIGH . LOW)' This kind of element indicates that an unmodified buffer became modified. The elements HIGH and LOW are two integers, each recording 16 bits of the visited file's modification time as of when it was previously visited or saved. `primitive-undo' uses those values to determine whether to mark the buffer as unmodified once again; it does so only if the file's modification time matches those numbers. `(nil PROPERTY VALUE BEG . END)' This kind of element records a change in a text property. Here's how you might undo the change: (put-text-property BEG END PROPERTY VALUE) `nil' This element is a boundary. The function `undo-boundary' adds these elements. The elements between two boundaries are called a "change group"; normally, each change group corresponds to one keyboard command, and undo commands normally undo an entire group as a unit. - Function: undo-boundary This function places a boundary element in the undo list. The undo command stops at such a boundary, and successive undo commands undo to earlier and earlier boundaries. This function returns `nil'. The editor command loop automatically creates an undo boundary between keystroke commands. Thus, each undo normally undoes the effects of one command. Calling this function explicitly is useful for splitting the effects of a command into more than one unit. For example, `query-replace' calls this function after each replacement so that the user can undo individual replacements one by one. - Function: primitive-undo COUNT LIST This is the basic function for undoing elements of an undo list. It undoes the first COUNT elements of LIST, returning the rest of LIST. You could write this function in Lisp, but it is convenient to have it in C. `primitive-undo' adds elements to the buffer's undo list. Undo commands avoid confusion by saving the undo list value at the beginning of a sequence of undo operations. Then the undo operations use and update the saved value. The new elements added by undoing never get into the saved value, so they don't cause any trouble. File: elisp, Node: Maintaining Undo, Next: Auto Filling, Prev: Undo, Up: Text Maintaining Undo Lists ====================== This section describes how to enable and disable undo information for a given buffer. It also explains how data from the undo list is discarded automatically so it doesn't get too big. Recording of undo information in a newly created buffer is normally enabled to start with; but if the buffer name starts with a space, the undo recording is initially disabled. You can explicitly enable or disable undo recording with the following two functions, or by setting `buffer-undo-list' yourself. - Command: buffer-enable-undo &optional BUFFER-OR-NAME This function enables recording undo information for buffer BUFFER-OR-NAME, so that subsequent changes can be undone. If no argument is supplied, then the current buffer is used. This function does nothing if undo recording is already enabled in the buffer. It returns `nil'. In an interactive call, BUFFER-OR-NAME is the current buffer. You cannot specify any other buffer. - Function: buffer-disable-undo BUFFER - Function: buffer-flush-undo BUFFER This function discards the undo list of BUFFER, and disables further recording of undo information. As a result, it is no longer possible to undo either previous changes or any subsequent changes. If the undo list of BUFFER is already disabled, this function has no effect. This function returns `nil'. It cannot be called interactively. The name `buffer-flush-undo' is not considered obsolete, but the preferred name `buffer-disable-undo' was not provided in Emacs versions 18 and earlier. As editing continues, undo lists get longer and longer. To prevent them from using up all available memory space, garbage collection trims them back to size limits you can set. (For this purpose, the "size" of an undo list measures the cons cells that make up the list, plus the strings of deleted text.) Two variables control the range of acceptable sizes: `undo-limit' and `undo-strong-limit'. - Variable: undo-limit This is the soft limit for the acceptable size of an undo list. The change group at which this size is exceeded is the last one kept. - Variable: undo-strong-limit The upper limit for the acceptable size of an undo list. The change group at which this size is exceeded is discarded itself (along with all subsequent changes). There is one exception: garbage collection always keeps the very last change group no matter how big it is. File: elisp, Node: Filling, Next: Sorting, Prev: Auto Filling, Up: Text Filling ======= "Filling" means adjusting the lengths of lines (by moving words between them) so that they are nearly (but no greater than) a specified maximum width. Additionally, lines can be "justified", which means that spaces are inserted between words to make the line exactly the specified width. The width is controlled by the variable `fill-column'. For ease of reading, lines should be no longer than 70 or so columns. You can use Auto Fill mode (*note Auto Filling::.) to fill text automatically as you insert it, but changes to existing text may leave it improperly filled. Then you must fill the text explicitly. Most of the functions in this section return values that are not meaningful. - Command: fill-paragraph JUSTIFY-FLAG This function fills the paragraph at or after point. If JUSTIFY-FLAG is non-`nil', each line is justified as well. It uses the ordinary paragraph motion commands to find paragraph boundaries. - Command: fill-region START END &optional JUSTIFY-FLAG This function fills each of the paragraphs in the region from START to END. It justifies as well if JUSTIFY-FLAG is non-`nil'. (In an interactive call, this is true if there is a prefix argument.) The variable `paragraph-separate' controls how to distinguish paragraphs. - Command: fill-individual-paragraphs START END &optional JUSTIFY-FLAG MAIL-FLAG This function fills each paragraph in the region according to its individual fill prefix. Thus, if the lines of a paragraph are indented with spaces, the filled paragraph will continue to be indented in the same fashion. The first two arguments, START and END, are the beginning and end of the region that will be filled. The third and fourth arguments, JUSTIFY-FLAG and MAIL-FLAG, are optional. If JUSTIFY-FLAG is non-`nil', the paragraphs are justified as well as filled. If MAIL-FLAG is non-`nil', the function is told that it is operating on a mail message and therefore should not fill the header lines. Ordinarily, `fill-individual-paragraphs' regards each change in indentation as starting a new paragraph. If `fill-individual-varying-indent' is non-`nil', then only separator lines separate paragraphs. That mode can handle paragraphs with extra indentation on the first line. - User Option: fill-individual-varying-indent This variable alters the action of `fill-individual-paragraphs' as described above. - Command: fill-region-as-paragraph START END &optional JUSTIFY-FLAG This function considers a region of text as a paragraph and fills it. If the region was made up of many paragraphs, the blank lines between paragraphs are removed. This function justifies as well as filling when JUSTIFY-FLAG is non-`nil'. In an interactive call, any prefix argument requests justification. In Adaptive Fill mode, which is enabled by default, `fill-region-as-paragraph' on an indented paragraph when there is no fill prefix uses the indentation of the second line of the paragraph as the fill prefix. - Command: justify-current-line This function inserts spaces between the words of the current line so that the line ends exactly at `fill-column'. It returns `nil'. - User Option: fill-column This buffer-local variable specifies the maximum width of filled lines. Its value should be an integer, which is a number of columns. All the filling, justification and centering commands are affected by this variable, including Auto Fill mode (*note Auto Filling::.). As a practical matter, if you are writing text for other people to read, you should set `fill-column' to no more than 70. Otherwise the line will be too long for people to read comfortably, and this can make the text seem clumsy. - Variable: default-fill-column The value of this variable is the default value for `fill-column' in buffers that do not override it. This is the same as `(default-value 'fill-column)'. The default value for `default-fill-column' is 70. File: elisp, Node: Auto Filling, Next: Filling, Prev: Maintaining Undo, Up: Text Auto Filling ============ "Filling" breaks text into lines that are no more than a specified number of columns wide. Filled lines end between words, and therefore may have to be shorter than the maximum width. Auto Fill mode is a minor mode in which Emacs fills lines automatically as text as inserted. This section describes the hook and the two variables used by Auto Fill mode. For a description of functions that you can call manually to fill and justify text, see *Note Filling::. - Variable: auto-fill-function The value of this variable should be a function (of no arguments) to be called after self-inserting a space at a column beyond `fill-column'. It may be `nil', in which case nothing special is done. The default value for `auto-fill-function' is `do-auto-fill', a function whose sole purpose is to implement the usual strategy for breaking a line. In older Emacs versions, this variable was named `auto-fill-hook', but since it is not called with the standard convention for hooks, it was renamed to `auto-fill-function' in version 19. File: elisp, Node: Sorting, Next: Indentation, Prev: Filling, Up: Text Sorting Text ============ The sorting commands described in this section all rearrange text in a buffer. This is in contrast to the function `sort', which rearranges the order of the elements of a list (*note Rearrangement::.). The values returned by these commands are not meaningful. - Command: sort-regexp-fields REVERSE RECORD-REGEXP KEY-REGEXP START END This command sorts the region between START and END alphabetically as specified by RECORD-REGEXP and KEY-REGEXP. If REVERSE is a negative integer, then sorting is in reverse order. Alphabetical sorting means that two sort keys are compared by comparing the first characters of each, the second characters of each, and so on. If a mismatch is found, it means that the sort keys are unequal; the sort key whose character is less at the point of first mismatch is the lesser sort key. The individual characters are compared according to their numerical values. Since Emacs uses the ASCII character set, the ordering in that set determines alphabetical order. The value of the RECORD-REGEXP argument specifies the textual units or "records" that should be sorted. At the end of each record, a search is done for this regular expression, and the text that matches it is the next record. For example, the regular expression `^.+$', which matches lines with at least one character besides a newline, would make each such line into a sort record. *Note Regular Expressions::, for a description of the syntax and meaning of regular expressions. The value of the KEY-REGEXP argument specifies what part of each record is to be compared against the other records. The KEY-REGEXP could match the whole record, or only a part. In the latter case, the rest of the record has no effect on the sorted order of records, but it is carried along when the record moves to its new position. The KEY-REGEXP argument can refer to the text matched by a subexpression of RECORD-REGEXP, or it can be a regular expression on its own. If KEY-REGEXP is: `\DIGIT' then the text matched by the DIGITth `$...$' parenthesis grouping in RECORD-REGEXP is used for sorting. `\&' then the whole record is used for sorting. a regular expression then the function searches for a match for the regular expression within the record. If such a match is found, it is used for sorting. If a match for KEY-REGEXP is not found within a record then that record is ignored, which means its position in the buffer is not changed. (The other records may move around it.) For example, if you plan to sort all the lines in the region by the first word on each line starting with the letter `f', you should set RECORD-REGEXP to `^.*$' and set KEY-REGEXP to `\<f\w*\>'. The resulting expression looks like this: (sort-regexp-fields nil "^.*$" "\\<f\\w*\\>" (region-beginning) (region-end)) If you call `sort-regexp-fields' interactively, you are prompted for RECORD-REGEXP and KEY-REGEXP in the minibuffer. - Command: sort-subr REVERSE NEXTRECFUN ENDRECFUN &optional STARTKEYFUN ENDKEYFUN This command is the general text sorting routine that divides a buffer into records and sorts them. The functions `sort-lines', `sort-paragraphs', `sort-pages', `sort-fields', `sort-regexp-fields' and `sort-numeric-fields' all use `sort-subr'. To understand how `sort-subr' works, consider the whole accessible portion of the buffer as being divided into disjoint pieces called "sort records". A portion of each sort record (perhaps all of it) is designated as the sort key. The records are rearranged in the buffer in order by their sort keys. The records may or may not be contiguous. Usually, the records are rearranged in order of ascending sort key. If the first argument to the `sort-subr' function, REVERSE, is non-`nil', the sort records are rearranged in order of descending sort key. The next four arguments to `sort-subr' are functions that are called to move point across a sort record. They are called many times from within `sort-subr'. 1. NEXTRECFUN is called with point at the end of a record. This function moves point to the start of the next record. The first record is assumed to start at the position of point when `sort-subr' is called. (Therefore, you should usually move point to the beginning of the buffer before calling `sort-subr'.) This function can indicate there are no more sort records by leaving point at the end of the buffer. 2. ENDRECFUN is called with point within a record. It moves point to the end of the record. 3. STARTKEYFUN is called to move point from the start of a record to the start of the sort key. This argument is optional. If supplied, the function should either return a non-`nil' value to be used as the sort key, or return `nil' to indicate that the sort key is in the buffer starting at point. In the latter case, ENDKEYFUN is called to find the end of the sort key. 4. ENDKEYFUN is called to move point from the start of the sort key to the end of the sort key. This argument is optional. If STARTKEYFUN returns `nil' and this argument is omitted (or `nil'), then the sort key extends to the end of the record. There is no need for ENDKEYFUN if STARTKEYFUN returns a non-`nil' value. As an example of `sort-subr', here is the complete function definition for `sort-lines': ;; Note that the first two lines of doc string ;; are effectively one line when viewed by a user. (defun sort-lines (reverse beg end) "Sort lines in region alphabetically;\ argument means descending order. Called from a program, there are three arguments: REVERSE (non-nil means reverse order), and BEG and END (the region to sort)." (interactive "P\nr") (save-restriction (narrow-to-region beg end) (goto-char (point-min)) (sort-subr reverse 'forward-line 'end-of-line))) Here `forward-line' moves point to the start of the next record, and `end-of-line' moves point to the end of record. We do not pass the arguments STARTKEYFUN and ENDKEYFUN, because the entire record is used as the sort key. The `sort-paragraphs' function is very much the same, except that its `sort-subr' call looks like this: (sort-subr reverse (function (lambda () (skip-chars-forward "\n \t\f"))) 'forward-paragraph) - Command: sort-lines REVERSE START END This command sorts lines in the region between START and END alphabetically. If REVERSE is non-`nil', the sort is in reverse order. - Command: sort-paragraphs REVERSE START END This command sorts paragraphs in the region between START and END alphabetically. If REVERSE is non-`nil', the sort is in reverse order. - Command: sort-pages REVERSE START END This command sorts pages in the region between START and END alphabetically. If REVERSE is non-`nil', the sort is in reverse order. - Command: sort-fields FIELD START END This command sorts lines in the region between START and END, comparing them alphabetically by the FIELDth field of each line. Fields are separated by whitespace and numbered starting from 1. If FIELD is negative, sorting is by the -FIELDth field from the end of the line. This command is useful for sorting tables. - Command: sort-numeric-fields FIELD START END This command sorts lines in the region between START and END, comparing them numerically by the FIELDth field of each line. Fields are separated by whitespace and numbered starting from 1. The specified field must contain a number in each line of the region. If FIELD is negative, sorting is by the -FIELDth field from the end of the line. This command is useful for sorting tables. - Command: sort-columns REVERSE &optional BEG END This command sorts the lines in the region between BEG and END, comparing them alphabetically by a certain range of columns. The column positions of BEG and END bound the range of columns to sort on. If REVERSE is non-`nil', the sort is in reverse order. One unusual thing about this command is that the entire line containing position BEG, and the entire line containing position END, are included in the region sorted. Note that `sort-columns' uses the `sort' utility program, and so cannot work properly on text containing tab characters. Use `M-x `untabify'' to convert tabs to spaces before sorting. The `sort-columns' function did not work on VMS prior to Emacs 19. File: elisp, Node: Indentation, Next: Columns, Prev: Sorting, Up: Text Indentation =========== The indentation functions are used to examine, move to, and change whitespace that is at the beginning of a line. Some of the functions can also change whitespace elsewhere on a line. Indentation always counts from zero at the left margin. * Menu: * Primitive Indent:: Functions used to count and insert indentation. * Mode-Specific Indent:: Customize indentation for different modes. * Region Indent:: Indent all the lines in a region. * Relative Indent:: Indent the current line based on previous lines. * Indent Tabs:: Adjustable, typewriter-like tab stops. * Motion by Indent:: Move to first non-blank character. File: elisp, Node: Primitive Indent, Next: Mode-Specific Indent, Up: Indentation Indentation Primitives ---------------------- This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives. - Function: current-indentation This function returns the indentation of the current line, which is the horizontal position of the first nonblank character. If the contents are entirely blank, then this is the horizontal position of the end of the line. - Command: indent-to COLUMN &optional MINIMUM This function indents from point with tabs and spaces until COLUMN is reached. If MINIMUM is specified and non-`nil', then at least that many spaces are inserted even if this requires going beyond COLUMN. The value is the column at which the inserted indentation ends. - User Option: indent-tabs-mode If this variable is non-`nil', indentation functions can insert tabs as well as spaces. Otherwise, they insert only spaces. Setting this variable automatically makes it local to the current buffer. File: elisp, Node: Mode-Specific Indent, Next: Region Indent, Prev: Primitive Indent, Up: Indentation Indentation Controlled by Major Mode ------------------------------------ An important function of each major mode is to customize the TAB key to indent properly for the language being edited. This section describes the mechanism of the TAB key and how to control it. The functions in this section return unpredictable values. - Variable: indent-line-function This variable's value is the function to be used by TAB (and various commands) to indent the current line. The command `indent-according-to-mode' does no more than call this function. In Lisp mode, the value is the symbol `lisp-indent-line'; in C mode, `c-indent-line'; in Fortran mode, `fortran-indent-line'. In Fundamental mode, Text mode, and many other modes with no standard for indentation, the value is `indent-to-left-margin' (which is the default value). - Command: indent-according-to-mode This command calls the function in `indent-line-function' to indent the current line in a way appropriate for the current major mode. - Command: indent-for-tab-command This command calls the function in `indent-line-function' to indent the current line, except that if that function is `indent-to-left-margin', `insert-tab' is called instead. (That is a trivial command which inserts a tab character.) - Variable: left-margin This variable is the column to which the default `indent-line-function' will indent. (That function is `indent-to-left-margin'.) In Fundamental mode, LFD indents to this column. This variable automatically becomes buffer-local when set in any fashion. - Function: indent-to-left-margin This is the default `indent-line-function', used in Fundamental mode, Text mode, etc. Its effect is to adjust the indentation at the beginning of the current line to the value specified by the variable `left-margin'. This may involve either inserting or deleting whitespace. - Command: newline-and-indent This function inserts a newline, then indents the new line (the one following the newline just inserted) according to the major mode. Indentation is done using the current `indent-line-function'. In programming language modes, this is the same thing TAB does, but in some text modes, where TAB inserts a tab, `newline-and-indent' indents to the column specified by `left-margin'. - Command: reindent-then-newline-and-indent This command reindents the current line, inserts a newline at point, and then reindents the new line (the one following the newline just inserted). Indentation of both lines is done according to the current major mode; this means that the current value of `indent-line-function' is called. In programming language modes, this is the same thing TAB does, but in some text modes, where TAB inserts a tab, `reindent-then-newline-and-indent' indents to the column specified by `left-margin'. File: elisp, Node: Region Indent, Next: Relative Indent, Prev: Mode-Specific Indent, Up: Indentation Indenting an Entire Region -------------------------- This section describes commands which indent all the lines in the region. They return unpredictable values. - Command: indent-region START END TO-COLUMN This command indents each nonblank line starting between START (inclusive) and END (exclusive). If TO-COLUMN is `nil', `indent-region' indents each nonblank line by calling the current mode's indentation function, the value of `indent-line-function'. If TO-COLUMN is non-`nil', it should be an integer specifying the number of columns of indentation; then this function gives each line exactly that much indentation, by either adding or deleting whitespace. If there is a fill prefix, `indent-region' indents each line by making it start with the fill prefix. - Variable: indent-region-function The value of this variable is a function that can be used by `indent-region' as a short cut. You should design the function so that it will produce the same results as indenting the lines of the region one by one (but presumably faster). If the value is `nil', there is no short cut, and `indent-region' actually works line by line. A short cut function is useful in modes such as C mode and Lisp mode, where the `indent-line-function' must scan from the beginning of the function: applying it to each line would be quadratic in time. The short cut can update the scan information as it moves through the lines indenting them; this takes linear time. If indenting a line individually is fast, there is no need for a short cut. `indent-region' with a non-`nil' argument has a different definition and does not use this variable. - Command: indent-rigidly START END COUNT This command indents all lines starting between START (inclusive) and END (exclusive) sideways by `count' columns. This "preserves the shape" of the affected region, moving it as a rigid unit. Consequently, this command is useful not only for indenting regions of unindented text, but also for indenting regions of formatted code. For example, if COUNT is 3, this command adds 3 columns of indentation to each of the lines beginning in the region specified. In Mail mode, `C-c C-y' (`mail-yank-original') uses `indent-rigidly' to indent the text copied from the message being replied to. - Function: indent-code-rigidly START END COLUMNS &optional NOCHANGE-REGEXP This is like `indent-rigidly', except that it doesn't alter lines that start within strings or comments. In addition, it doesn't alter a line if NOCHANGE-REGEXP matches at the beginning of the line (if NOCHANGE-REGEXP is non-`nil'). File: elisp, Node: Relative Indent, Next: Indent Tabs, Prev: Region Indent, Up: Indentation Indentation Relative to Previous Lines -------------------------------------- This section describes two commands which indent the current line based on the contents of previous lines. - Command: indent-relative &optional UNINDENTED-OK This function inserts whitespace at point, extending to the same column as the next "indent point" of the previous nonblank line. An indent point is a non-whitespace character following whitespace. The next indent point is the first one at a column greater than the current column of point. For example, if point is underneath and to the left of the first non-blank character of a line of text, it moves to that column by inserting whitespace. If the previous nonblank line has no next indent point (i.e., none at a great enough column position), this function either does nothing (if UNINDENTED-OK is non-`nil') or calls `tab-to-tab-stop'. Thus, if point is underneath and to the right of the last column of a short line of text, this function moves point to the next tab stop by inserting whitespace. This command returns an unpredictable value. In the following example, point is at the beginning of the second line: This line is indented twelve spaces. -!-The quick brown fox jumped. Evaluation of the expression `(indent-relative nil)' produces the following: This line is indented twelve spaces. -!-The quick brown fox jumped. In this example, point is between the `m' and `p' of `jumped': This line is indented twelve spaces. The quick brown fox jum-!-ped. Evaluation of the expression `(indent-relative nil)' produces the following: This line is indented twelve spaces. The quick brown fox jum -!-ped. - Command: indent-relative-maybe This command indents the current line like the previous nonblank line. The function consists of a call to `indent-relative' with a non-`nil' value passed to the UNINDENTED-OK optional argument. The value is unpredictable. If the previous line has no indentation, the current line is given no indentation (any existing indentation is deleted); if the previous nonblank line has no indent points beyond the column at which point starts, nothing is changed. File: elisp, Node: Indent Tabs, Next: Motion by Indent, Prev: Relative Indent, Up: Indentation Adjustable "Tab Stops" ---------------------- This section explains the mechanism for user-specified "tab stops" and the mechanisms which use and set them. The name "tab stops" is used because the feature is similar to that of the tab stops on a typewriter. The feature works by inserting an appropriate number of spaces and tab characters to reach the designated position, like the other indentation functions; it does not affect the display of tab characters in the buffer (*note Usual Display::.). Note that the TAB character as input uses this tab stop feature only in a few major modes, such as Text mode. - Function: tab-to-tab-stop This function inserts spaces or tabs up to the next tab stop column defined by `tab-stop-list'. It searches the list for an element greater than the current column number, and uses that element as the column to indent to. If no such element is found, then nothing is done. - User Option: tab-stop-list This variable is the list of tab stop columns used by `tab-to-tab-stops'. The elements should be integers in increasing order. The tab stop columns need not be evenly spaced. Use `M-x edit-tab-stops' to edit the location of tab stops interactively. File: elisp, Node: Motion by Indent, Prev: Indent Tabs, Up: Indentation Indentation-Based Motion Commands --------------------------------- These commands, primarily for interactive use, act based on the indentation in the text. - Command: back-to-indentation This command moves point to the first non-whitespace character in the current line (which is the line in which point is located). It returns `nil'. - Command: backward-to-indentation ARG This command moves point backward ARG lines and then to the first nonblank character on that line. It returns `nil'. - Command: forward-to-indentation ARG This command moves point forward ARG lines and then to the first nonblank character on that line. It returns `nil'. File: elisp, Node: Columns, Next: Case Changes, Prev: Indentation, Up: Text Counting Columns ================ The column functions convert between a character position (counting characters from the beginning of the buffer) and a column position (counting screen characters from the beginning of a line). Column number computations ignore the width of the window and the amount of horizontal scrolling. Consequently, a column value can be arbitrarily high. The first (or leftmost) column is numbered 0. A character counts according to the number of columns it occupies on the screen. This means control characters count as occupying 2 or 4 columns, depending upon the value of `ctl-arrow', and tabs count as occupying a number of columns that depends on the value of `tab-width' and on the column where the tab begins. *Note Usual Display::. - Function: current-column This function returns the horizontal position of point, measured in columns, counting from 0 at the left margin. The column count is calculated by adding together the widths of all the displayed representations of the characters between the start of the current line and point. For a more complicated example of the use of `current-column', see the description of `count-lines' in *Note Text Lines::. - Function: move-to-column COLUMN &optional FORCE This function moves point to COLUMN in the current line. The calculation of COLUMN takes into account the widths of all the displayed representations of the characters between the start of the line and point. If the argument COLUMN is greater than the column position of the end of the line, point moves to the end of the line. If COLUMN is negative, point moves to the beginning of the line. If it is impossible to move to column COLUMN because that is in the middle of a multicolumn character such as a tab, point moves to the end of that character. However, if FORCE is non-`nil', and COLUMN is in the middle of a tab, then `move-to-column' converts the tab into spaces so that it can move precisely to column COLUMN. The argument FORCE also has an effect if the line isn't long enough to reach column COLUMN; in that case, it says to indent at the end of the line to reach that column. If COLUMN is not an integer, an error is signaled. The return value is the column number actually moved to.