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* doc/lispref/modes.texi (Auto-Indentation): New section to document SMIE.

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(Major Mode Conventions):
* doc/lispref/text.texi (Mode-Specific Indent): Refer to it.
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Stefan Monnier 2010-12-07 14:44:38 -05:00
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206
doc/lispref/ChangeLog
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@ -1,3 +1,9 @@
2010-12-07 Stefan Monnier <monnier@iro.umontreal.ca>
* modes.texi (Auto-Indentation): New section to document SMIE.
(Major Mode Conventions):
* text.texi (Mode-Specific Indent): Refer to it.
2010-12-04 Eli Zaretskii <eliz@gnu.org>
* display.texi (Other Display Specs): Document left-fringe and
@ -12,8 +18,8 @@
2010-11-21 Chong Yidong <cyd@stupidchicken.com>
* nonascii.texi (Converting Representations): Document
byte-to-string.
* nonascii.texi (Converting Representations):
Document byte-to-string.
* strings.texi (Creating Strings): Don't mention semi-obsolete
function char-to-string.
@ -44,8 +50,8 @@
* customize.texi (Composite Types): Lower-case index entry.
* loading.texi (How Programs Do Loading): Document
load-file-name. (Bug#7346)
* loading.texi (How Programs Do Loading):
Document load-file-name. (Bug#7346)
2010-11-10 Glenn Morris <rgm@gnu.org>
@ -152,8 +158,8 @@
* keymaps.texi (Menu Bar): Document :advertised-binding property.
* functions.texi (Obsolete Functions): Document
set-advertised-calling-convention.
* functions.texi (Obsolete Functions):
Document set-advertised-calling-convention.
* minibuf.texi (Basic Completion): Document completion-in-region.
(Programmed Completion): Document completion-annotate-function.
@ -278,8 +284,8 @@
* minibuf.texi (Basic Completion): 4th arg to all-completions is
obsolete.
* processes.texi (Process Buffers): Document
process-kill-buffer-query-function.
* processes.texi (Process Buffers):
Document process-kill-buffer-query-function.
2009-12-05 Glenn Morris <rgm@gnu.org>
@ -726,8 +732,8 @@
(Suspending Emacs): Mark suspend-emacs as a command.
(Processor Run Time): Mark emacs-uptime and emacs-init-time as
commands.
(Terminal Output): Remove obsolete function baud-rate. Document
TERMINAL arg for send-string-to-terminal.
(Terminal Output): Remove obsolete function baud-rate.
Document TERMINAL arg for send-string-to-terminal.
* nonascii.texi (Terminal I/O Encoding): Document TERMINAL arg for
terminal-coding-system and set-terminal-coding-system.
@ -831,8 +837,8 @@
2009-05-09 Eli Zaretskii <eliz@gnu.org>
* nonascii.texi (Default Coding Systems): Document
find-auto-coding, set-auto-coding, and auto-coding-alist. Add
indexing.
find-auto-coding, set-auto-coding, and auto-coding-alist.
Add indexing.
(Lisp and Coding Systems): Add index entries.
2009-05-09 Martin Rudalics <rudalics@gmx.at>
@ -874,8 +880,8 @@
2009-04-22 Chong Yidong <cyd@stupidchicken.com>
* os.texi (Command-Line Arguments): Document
command-line-args-left.
* os.texi (Command-Line Arguments):
Document command-line-args-left.
(Suspending Emacs): Adapt text to multi-tty case. Document use of
terminal objects for tty arguments.
(Startup Summary): Add xref to Session Management.
@ -951,13 +957,13 @@
2009-04-09 Chong Yidong <cyd@stupidchicken.com>
* text.texi (Yank Commands): Note that yank uses push-mark.
(Filling): Clarify REGION argument of fill-paragraph. Document
fill-forward-paragraph-function.
(Filling): Clarify REGION argument of fill-paragraph.
Document fill-forward-paragraph-function.
(Special Properties): Remove "new in Emacs 22" declaration.
(Clickable Text): Merge with Links and Mouse-1 node.
* display.texi (Button Properties, Button Buffer Commands): Change
xref to Clickable Text.
* display.texi (Button Properties, Button Buffer Commands):
Change xref to Clickable Text.
* tips.texi (Key Binding Conventions): Change xref to Clickable
Text.
@ -1019,8 +1025,8 @@
2009-03-29 Chong Yidong <cyd@stupidchicken.com>
* help.texi (Accessing Documentation, Help Functions): Remove
information about long-obsolete Emacs versions.
* help.texi (Accessing Documentation, Help Functions):
Remove information about long-obsolete Emacs versions.
* modes.texi (Mode Line Variables): The default values of the mode
line variables are now more complicated.
@ -1063,8 +1069,8 @@
2009-03-23 Chong Yidong <cyd@stupidchicken.com>
* minibuf.texi (Intro to Minibuffers): Remove long-obsolete info
about minibuffers in old Emacs versions. Copyedits. Emphasize
that enable-recursive-minibuffers defaults to nil.
about minibuffers in old Emacs versions. Copyedits.
Emphasize that enable-recursive-minibuffers defaults to nil.
(Text from Minibuffer): Simplify introduction.
2009-03-22 Alan Mackenzie <acm@muc.de>
@ -1118,8 +1124,8 @@
* customize.texi (Common Keywords): It's not necessary to use :tag
to remove hyphens, as custom-unlispify-tag-name does it
automatically.
(Variable Definitions): Link to File Local Variables. Document
customized-value symbol property.
(Variable Definitions): Link to File Local Variables.
Document customized-value symbol property.
(Customization Types): Move menu to end of node.
2009-03-10 Chong Yidong <cyd@stupidchicken.com>
@ -1230,8 +1236,8 @@
* text.texi (Commands for Insertion):
* commands.texi (Event Mod):
* keymaps.texi (Searching Keymaps):
* nonascii.texi (Translation of Characters): Reinstate
documentation of translation-table-for-input.
* nonascii.texi (Translation of Characters):
Reinstate documentation of translation-table-for-input.
(Explicit Encoding): Document the `charset' text property produced
by decode-coding-region and decode-coding-string.
@ -1260,8 +1266,8 @@
2009-01-22 Chong Yidong <cyd@stupidchicken.com>
* files.texi (Format Conversion Piecemeal): Clarify behavior of
write-region-annotate-functions. Document
write-region-post-annotation-function.
write-region-annotate-functions.
Document write-region-post-annotation-function.
2009-01-19 Chong Yidong <cyd@stupidchicken.com>
@ -1328,8 +1334,8 @@
* processes.texi (Serial Ports): Improve wording, suggested by RMS.
* nonascii.texi (Lisp and Coding Systems): Document
inhibit-null-byte-detection and inhibit-iso-escape-detection.
* nonascii.texi (Lisp and Coding Systems):
Document inhibit-null-byte-detection and inhibit-iso-escape-detection.
(Character Properties): Improve wording.
2009-01-09 Chong Yidong <cyd@stupidchicken.com>
@ -1337,8 +1343,8 @@
* display.texi (Font Lookup): Remove obsolete function
x-font-family-list. x-list-fonts accepts Fontconfig/GTK syntax.
(Low-Level Font): Rename from Fonts, move to end of Faces section.
(Font Selection): Reorder order of variable descriptions. Minor
clarifications.
(Font Selection): Reorder order of variable descriptions.
Minor clarifications.
* elisp.texi (Top): Update node listing.
@ -1359,8 +1365,8 @@
* elisp.texi: Update node listing.
* display.texi (Faces): Put Font Selection node after Auto Faces.
(Face Attributes): Don't link to Font Lookup. Document
font-family-list.
(Face Attributes): Don't link to Font Lookup.
Document font-family-list.
(Fonts): New node.
2009-01-08 Jason Rumney <jasonr@gnu.org>
@ -1588,8 +1594,8 @@
* windows.texi (Window Hooks): Remove *-end-trigger-functions
vars, which are obsolete. Mention jit-lock-register.
* modes.texi (Other Font Lock Variables): Document
jit-lock-register and jit-lock-unregister.
* modes.texi (Other Font Lock Variables):
Document jit-lock-register and jit-lock-unregister.
* frames.texi (Color Parameters): Document alpha parameter.
@ -1661,8 +1667,8 @@
2008-11-01 Eli Zaretskii <eliz@gnu.org>
* nonascii.texi (Text Representations): Rewrite to make consistent
with Emacs 23 internal representation of characters. Document
`unibyte-string'.
with Emacs 23 internal representation of characters.
Document `unibyte-string'.
2008-10-28 Chong Yidong <cyd@stupidchicken.com>
@ -1775,8 +1781,8 @@
* processes.texi (Synchronous Processes): Document `process-lines'.
* customize.texi (Variable Definitions): Document
`custom-reevaluate-setting'.
* customize.texi (Variable Definitions):
Document `custom-reevaluate-setting'.
2008-10-18 Martin Rudalics <rudalics@gmx.at>
@ -1792,13 +1798,13 @@
* maps.texi (Standard Keymaps): Document `multi-query-replace-map'
and `search-map'.
* searching.texi (Search and Replace): Document
`replace-search-function' and `replace-re-search-function'.
* searching.texi (Search and Replace):
Document `replace-search-function' and `replace-re-search-function'.
Document `multi-query-replace-map'.
* minibuf.texi (Text from Minibuffer): Document `read-regexp'.
(Completion Commands, Reading File Names): Rename
`minibuffer-local-must-match-filename-map' to
(Completion Commands, Reading File Names):
Rename `minibuffer-local-must-match-filename-map' to
`minibuffer-local-filename-must-match-map'.
(Minibuffer Completion): The `require-match' argument to
`completing-read' can now have the value `confirm-only'.
@ -2143,7 +2149,7 @@
2007-12-30 Richard Stallman <rms@gnu.org>
* commands.texi (Accessing Mouse): Renamed from Accessing Events.
* commands.texi (Accessing Mouse): Rename from Accessing Events.
(Accessing Scroll): New node broken out of Accessing Mouse.
2007-12-28 Richard Stallman <rms@gnu.org>
@ -2187,8 +2193,8 @@
2007-11-29 Glenn Morris <rgm@gnu.org>
* functions.texi (Declaring Functions): Add findex. Mention
`external' files.
* functions.texi (Declaring Functions): Add findex.
Mention `external' files.
2007-11-26 Juanma Barranquero <lekktu@gmail.com>
@ -2315,8 +2321,8 @@
* display.texi (Display Property): Explain some display specs
don't let you move point in.
* frames.texi (Cursor Parameters): Describe
cursor-in-non-selected-windows here. Explain more values.
* frames.texi (Cursor Parameters):
Describe cursor-in-non-selected-windows here. Explain more values.
* windows.texi (Basic Windows): Don't describe
cursor-in-non-selected-windows here.
@ -2395,8 +2401,8 @@
2007-08-16 Richard Stallman <rms@gnu.org>
* processes.texi (Asynchronous Processes): Clarify
doc of start-file-process.
* processes.texi (Asynchronous Processes):
Clarify doc of start-file-process.
2007-08-08 Martin Rudalics <rudalics@gmx.at>
@ -2463,8 +2469,8 @@
2007-06-27 Richard Stallman <rms@gnu.org>
* files.texi (Format Conversion Piecemeal): Clarify
`after-insert-file-functions' calling convention.
* files.texi (Format Conversion Piecemeal):
Clarify `after-insert-file-functions' calling convention.
2007-06-27 Michael Albinus <michael.albinus@gmx.de>
@ -2519,8 +2525,8 @@
2007-05-30 Nick Roberts <nickrob@snap.net.nz>
* commands.texi (Click Events): Layout more logically. Describe
width and height.
* commands.texi (Click Events): Layout more logically.
Describe width and height.
(Drag Events, Motion Events): Update to new format for position.
2007-06-02 Richard Stallman <rms@gnu.org>
@ -2926,8 +2932,8 @@
2007-03-05 Richard Stallman <rms@gnu.org>
* variables.texi (File Local Variables): Update
enable-local-variables values.
* variables.texi (File Local Variables):
Update enable-local-variables values.
2007-03-04 Richard Stallman <rms@gnu.org>
@ -2998,8 +3004,8 @@
2007-02-03 Eli Zaretskii <eliz@gnu.org>
* elisp.texi (Top): Make the detailed menu headers compliant with
Texinfo guidelines and with what texnfo-upd.el expects. Add
comments to prevent people from inadvertently modifying the key
Texinfo guidelines and with what texnfo-upd.el expects.
Add comments to prevent people from inadvertently modifying the key
parts needed by `texinfo-multiple-files-update'.
2007-02-02 Eli Zaretskii <eliz@gnu.org>
@ -3086,8 +3092,8 @@
2006-12-24 Richard Stallman <rms@gnu.org>
* customize.texi (Variable Definitions): Document
new name custom-add-frequent-value.
* customize.texi (Variable Definitions):
Document new name custom-add-frequent-value.
2006-12-19 Kim F. Storm <storm@cua.dk>
@ -3386,8 +3392,8 @@
2006-09-01 Chong Yidong <cyd@stupidchicken.com>
* buffers.texi (Buffer Modification): Document
buffer-chars-modified-tick.
* buffers.texi (Buffer Modification):
Document buffer-chars-modified-tick.
2006-08-31 Richard Stallman <rms@gnu.org>
@ -3449,7 +3455,7 @@
2006-08-12 Chong Yidong <cyd@stupidchicken.com>
* text.texi (Near Point): Say "cursor" not "terminal cursor".
(Commands for Insertion): Removed split-line since it's not
(Commands for Insertion): Remove split-line since it's not
relevant for Lisp programming.
(Yank Commands): Rewrite introduction.
(Undo): Clarify.
@ -3480,7 +3486,7 @@
(Major Mode Basics): Mention define-derived-mode explicitly.
(Major Mode Conventions): Rebinding RET is OK for some modes.
Mention change-major-mode-hook and after-change-major-mode-hook.
(Example Major Modes): Moved to end of Modes section.
(Example Major Modes): Move to end of Modes section.
(Mode Line Basics): Clarify.
(Mode Line Data): Mention help-echo and local-map in strings.
Explain reason for treatment of non-risky variables.
@ -3979,7 +3985,7 @@
2006-05-25 Chong Yidong <cyd@stupidchicken.com>
* keymaps.texi (Key Sequences): Renamed from Keymap Terminology.
* keymaps.texi (Key Sequences): Rename from Keymap Terminology.
Explain string and vector representations of key sequences.
* keymaps.texi (Changing Key Bindings):
@ -4028,8 +4034,8 @@
2006-05-15 Oliver Scholz <epameinondas@gmx.de> (tiny change)
* nonascii.texi (Explicit Encoding): Fix
typo (encoding<->decoding).
* nonascii.texi (Explicit Encoding):
Fix typo (encoding<->decoding).
2006-05-14 Richard Stallman <rms@gnu.org>
@ -4079,8 +4085,8 @@
2006-05-09 Richard Stallman <rms@gnu.org>
* variables.texi (File Local Variables): Document
safe-local-eval-forms and safe-local-eval-function.
* variables.texi (File Local Variables):
Document safe-local-eval-forms and safe-local-eval-function.
2006-05-07 Kim F. Storm <storm@cua.dk>
@ -4564,8 +4570,8 @@
2005-12-03 Eli Zaretskii <eliz@gnu.org>
* hooks.texi (Standard Hooks): Add index entries. Mention
`compilation-finish-functions'.
* hooks.texi (Standard Hooks): Add index entries.
Mention `compilation-finish-functions'.
2005-11-27 Richard M. Stallman <rms@gnu.org>
@ -4788,8 +4794,8 @@
buffer-local.
(Undo): Note that buffer-undo-list is buffer-local.
* windows.texi (Buffers and Windows): Document
buffer-display-count.
* windows.texi (Buffers and Windows):
Document buffer-display-count.
2005-09-06 Richard M. Stallman <rms@gnu.org>
@ -5030,7 +5036,7 @@
* display.texi (Displaying Messages): New node, with most
of what was in The Echo Area.
(Progress): Moved under The Echo Area.
(Progress): Move under The Echo Area.
(Logging Messages): New node with new text.
(Echo Area Customization): New node, the rest of what was
in The Echo Area. Document message-truncate-lines with @defvar.
@ -6345,8 +6351,8 @@
(Scroll Bars): Add scroll-bar-mode and scroll-bar-width.
(Usual Display): Move tab-width up.
* customize.texi (Variable Definitions): Replace
show-paren-mode example with tooltip-mode.
* customize.texi (Variable Definitions):
Replace show-paren-mode example with tooltip-mode.
(Simple Types, Composite Types, Defining New Types):
Minor cleanups.
@ -6582,8 +6588,8 @@
(Display Fringe Bitmaps): New node.
(Images): Add 'Image Slices' to menu.
(Image Descriptors): Add `:pointer' and `:map' properties.
(Showing Images): Add slice arg to `insert-image'. Add
'insert-sliced-image'.
(Showing Images): Add slice arg to `insert-image'.
Add 'insert-sliced-image'.
2004-09-20 Richard M. Stallman <rms@gnu.org>
@ -6596,8 +6602,8 @@
2004-09-07 Luc Teirlinck <teirllm@auburn.edu>
* locals.texi (Standard Buffer-Local Variables): Add
`buffer-auto-save-file-format'.
* locals.texi (Standard Buffer-Local Variables):
Add `buffer-auto-save-file-format'.
* internals.texi (Buffer Internals): Describe new
auto_save_file_format field of the buffer structure.
* files.texi (Format Conversion): `auto-save-file-format' has been
@ -6985,8 +6991,8 @@
2004-04-05 Jesper Harder <harder@ifa.au.dk>
* variables.texi (Variable Aliases): Mention
cyclic-variable-indirection.
* variables.texi (Variable Aliases):
Mention cyclic-variable-indirection.
* errors.texi (Standard Errors): Ditto.
@ -7165,7 +7171,7 @@
2004-02-07 Jan Djärv <jan.h.d@swipnet.se>
* positions.texi (Text Lines): Added missing end defun.
* positions.texi (Text Lines): Add missing end defun.
2004-02-07 Kim F. Storm <storm@cua.dk>
@ -7188,12 +7194,12 @@
read-minibuffer.
(Minibuffer History): Clarify description of cons values for
HISTORY arguments.
(Basic Completion): Various corrections and clarifications. Add
completion-regexp-list.
(Basic Completion): Various corrections and clarifications.
Add completion-regexp-list.
(Minibuffer Completion): Correct and clarify description of
completing-read.
(Completion Commands): Mention Partial Completion mode. Various
other minor changes.
(Completion Commands): Mention Partial Completion mode.
Various other minor changes.
(High-Level Completion): Various corrections and clarifications.
(Reading File Names): Ditto.
(Minibuffer Misc): Ditto.
@ -7268,8 +7274,8 @@
* functions.texi: Various small changes in addition to the
following.
(What Is a Function): `functionp' returns nil for macros. Clarify
behavior of this and following functions for symbol arguments.
(What Is a Function): `functionp' returns nil for macros.
Clarify behavior of this and following functions for symbol arguments.
(Function Documentation): Add `\' in front of (fn @var{arglist})
and explain why.
(Defining Functions): Mention DOCSTRING argument to `defalias'.
@ -8065,7 +8071,7 @@
2003-01-31 Joe Buehler <jhpb@draco.hekimian.com>
* os.texi (System Environment): Added cygwin system-type.
* os.texi (System Environment): Add cygwin system-type.
2003-01-25 Richard M. Stallman <rms@gnu.org>
@ -8098,7 +8104,7 @@
* README: Target for Info file is `make info'.
* files.texi (File Name Components): Fixed typos in
* files.texi (File Name Components): Fix typos in
`file-name-sans-extension'.
(Magic File Names): Complete list of operations for magic file
name handlers.
@ -8114,7 +8120,7 @@
2002-08-05 Per Abrahamsen <abraham@dina.kvl.dk>
* customize.texi (Splicing into Lists): Fixed example.
* customize.texi (Splicing into Lists): Fix example.
Reported by Fabrice Bauzac <fabrice.bauzac@wanadoo.fr>.
2002-06-17 Juanma Barranquero <lektu@terra.es>
@ -8154,8 +8160,8 @@
2001-11-17 Eli Zaretskii <eliz@is.elta.co.il>
* permute-index: Don't depend on csh-specific features. Replace
the interpreter name with /bin/sh.
* permute-index: Don't depend on csh-specific features.
Replace the interpreter name with /bin/sh.
* two-volume-cross-refs.txt: New file.
* two.el: New file.
@ -8293,8 +8299,8 @@
* numbers.texi (Integer Basics): Document CL style read syntax for
integers in bases other than 10.
* positions.texi (List Motion): Document
open-paren-in-column-0-is-defun-start.
* positions.texi (List Motion):
Document open-paren-in-column-0-is-defun-start.
* lists.texi (Sets And Lists): Document member-ignore-case.
@ -8489,7 +8495,7 @@
1995-06-19 Richard Stallman <rms@mole.gnu.ai.mit.edu>
* Makefile (VERSION): Update version number.
(maintainer-clean): Renamed from realclean.
(maintainer-clean): Rename from realclean.
1995-06-07 Karl Heuer <kwzh@nutrimat.gnu.ai.mit.edu>
@ -8561,11 +8567,11 @@
1991-11-26 Richard Stallman (rms@mole.gnu.ai.mit.edu)
* Makefile (srcs): Added index.perm.
* Makefile (srcs): Add index.perm.
(elisp.dvi): Remove erroneous shell comment.
Expect output of permute-index in permuted.fns.
Save old elisp.aux in elisp.oaux.
(clean): Added index.texi to be deleted.
(clean): Add index.texi to be deleted.
1990-08-11 Richard Stallman (rms@sugar-bombs.ai.mit.edu)

668
doc/lispref/modes.texi
View file

@ -24,10 +24,11 @@ user. For related topics such as keymaps and syntax tables, see
* Major Modes:: Defining major modes.
* Minor Modes:: Defining minor modes.
* Mode Line Format:: Customizing the text that appears in the mode line.
* Imenu:: How a mode can provide a menu
* Imenu:: How a mode can provide a menu
of definitions in the buffer.
* Font Lock Mode:: How modes can highlight text according to syntax.
* Desktop Save Mode:: How modes can have buffer state saved between
* Font Lock Mode:: How modes can highlight text according to syntax.
* Auto-Indentation:: How to teach Emacs to indent for a major mode.
* Desktop Save Mode:: How modes can have buffer state saved between
Emacs sessions.
@end menu
@ -332,7 +333,7 @@ In a major mode for editing some kind of structured text, such as a
programming language, indentation of text according to structure is
probably useful. So the mode should set @code{indent-line-function}
to a suitable function, and probably customize other variables
for indentation.
for indentation. @xref{Auto-Indentation}.
@item
@cindex keymaps in modes
@ -3214,6 +3215,665 @@ Since this function is called after every buffer change, it should be
reasonably fast.
@end defvar
@node Auto-Indentation
@section Auto-indention of code
For programming languages, an important feature of a major mode is to
provide automatic indentation. This is controlled in Emacs by
@code{indent-line-function} (@pxref{Mode-Specific Indent}).
Writing a good indentation function can be difficult and to a large
extent it is still a black art.
Many major mode authors will start by writing a simple indentation
function that works for simple cases, for example by comparing with the
indentation of the previous text line. For most programming languages
that are not really line-based, this tends to scale very poorly:
improving such a function to let it handle more diverse situations tends
to become more and more difficult, resulting in the end with a large,
complex, unmaintainable indentation function which nobody dares to touch.
A good indentation function will usually need to actually parse the
text, according to the syntax of the language. Luckily, it is not
necessary to parse the text in as much detail as would be needed
for a compiler, but on the other hand, the parser embedded in the
indentation code will want to be somewhat friendly to syntactically
incorrect code.
Good maintainable indentation functions usually fall into 2 categories:
either parsing forward from some ``safe'' starting point until the
position of interest, or parsing backward from the position of interest.
Neither of the two is a clearly better choice than the other: parsing
backward is often more difficult than parsing forward because
programming languages are designed to be parsed forward, but for the
purpose of indentation it has the advantage of not needing to
guess a ``safe'' starting point, and it generally enjoys the property
that only a minimum of text will be analyzed to decide the indentation
of a line, so indentation will tend to be unaffected by syntax errors in
some earlier unrelated piece of code. Parsing forward on the other hand
is usually easier and has the advantage of making it possible to
reindent efficiently a whole region at a time, with a single parse.
Rather than write your own indentation function from scratch, it is
often preferable to try and reuse some existing ones or to rely
on a generic indentation engine. There are sadly few such
engines. The CC-mode indentation code (used with C, C++, Java, Awk
and a few other such modes) has been made more generic over the years,
so if your language seems somewhat similar to one of those languages,
you might try to use that engine. @c FIXME: documentation?
Another one is SMIE which takes an approach in the spirit
of Lisp sexps and adapts it to non-Lisp languages.
@menu
* SMIE:: A simple minded indentation engine
@end menu
@node SMIE
@subsection Simple Minded Indentation Engine
SMIE is a package that provides a generic navigation and indentation
engine. Based on a very simple parser using an ``operator precedence
grammar'', it lets major modes extend the sexp-based navigation of Lisp
to non-Lisp languages as well as provide a simple to use but reliable
auto-indentation.
Operator precedence grammar is a very primitive technology for parsing
compared to some of the more common techniques used in compilers.
It has the following characteristics: its parsing power is very limited,
and it is largely unable to detect syntax errors, but it has the
advantage of being algorithmically efficient and able to parse forward
just as well as backward. In practice that means that SMIE can use it
for indentation based on backward parsing, that it can provide both
@code{forward-sexp} and @code{backward-sexp} functionality, and that it
will naturally work on syntactically incorrect code without any extra
effort. The downside is that it also means that most programming
languages cannot be parsed correctly using SMIE, at least not without
resorting to some special tricks (@pxref{SMIE Tricks}).
@menu
* SMIE setup:: SMIE setup and features
* Operator Precedence Grammars:: A very simple parsing technique
* SMIE Grammar:: Defining the grammar of a language
* SMIE Lexer:: Defining tokens
* SMIE Tricks:: Working around the parser's limitations
* SMIE Indentation:: Specifying indentation rules
* SMIE Indentation Helpers:: Helper functions for indentation rules
* SMIE Indentation Example:: Sample indentation rules
@end menu
@node SMIE setup
@subsubsection SMIE Setup and Features
SMIE is meant to be a one-stop shop for structural navigation and
various other features which rely on the syntactic structure of code, in
particular automatic indentation. The main entry point is
@code{smie-setup} which is a function typically called while setting
up a major mode.
@defun smie-setup grammar rules-function &rest keywords
Setup SMIE navigation and indentation.
@var{grammar} is a grammar table generated by @code{smie-prec2->grammar}.
@var{rules-function} is a set of indentation rules for use on
@code{smie-rules-function}.
@var{keywords} are additional arguments, which can include the following
keywords:
@itemize
@item
@code{:forward-token} @var{fun}: Specify the forward lexer to use.
@item
@code{:backward-token} @var{fun}: Specify the backward lexer to use.
@end itemize
@end defun
Calling this function is sufficient to make commands such as
@code{forward-sexp}, @code{backward-sexp}, and @code{transpose-sexps} be
able to properly handle structural elements other than just the paired
parentheses already handled by syntax tables. For example, if the
provided grammar is precise enough, @code{transpose-sexps} can correctly
transpose the two arguments of a @code{+} operator, taking into account
the precedence rules of the language.
Calling `smie-setup' is also sufficient to make TAB indentation work in
the expected way, and provides some commands that you can bind in the
major mode keymap.
@deffn Command smie-close-block
This command closes the most recently opened (and not yet closed) block.
@end deffn
@deffn Command smie-down-list &optional arg
This command is like @code{down-list} but it also pays attention to
nesting of tokens other than parentheses, such as @code{begin...end}.
@end deffn
@node Operator Precedence Grammars
@subsubsection Operator Precedence Grammars
SMIE's precedence grammars simply give to each token a pair of
precedences: the left-precedence and the right-precedence. We say
@code{T1 < T2} if the right-precedence of token @code{T1} is less than
the left-precedence of token @code{T2}. A good way to read this
@code{<} is as a kind of parenthesis: if we find @code{... T1 something
T2 ...} then that should be parsed as @code{... T1 (something T2 ...}
rather than as @code{... T1 something) T2 ...}. The latter
interpretation would be the case if we had @code{T1 > T2}. If we have
@code{T1 = T2}, it means that token T2 follows token T1 in the same
syntactic construction, so typically we have @code{"begin" = "end"}.
Such pairs of precedences are sufficient to express left-associativity
or right-associativity of infix operators, nesting of tokens like
parentheses and many other cases.
@c ¡Let's leave this undocumented to leave it more open for change!
@c @defvar smie-grammar
@c The value of this variable is an alist specifying the left and right
@c precedence of each token. It is meant to be initialized by using one of
@c the functions below.
@c @end defvar
@defun smie-prec2->grammar table
This function takes a @emph{prec2} grammar @var{table} and returns an
alist suitable for use in @code{smie-setup}. The @emph{prec2}
@var{table} is itself meant to be built by one of the functions below.
@end defun
@defun smie-merge-prec2s &rest tables
This function takes several @emph{prec2} @var{tables} and merges them
into a new @emph{prec2} table.
@end defun
@defun smie-precs->prec2 precs
This function builds a @emph{prec2} table from a table of precedences
@var{precs}. @var{precs} should be a list, sorted by precedence (for
example @code{"+"} will come before @code{"*"}), of elements of the form
@code{(@var{assoc} @var{op} ...)}, where each @var{op} is a token that
acts as an operator; @var{assoc} is their associativity, which can be
either @code{left}, @code{right}, @code{assoc}, or @code{nonassoc}.
All operators in a given element share the same precedence level
and associativity.
@end defun
@defun smie-bnf->prec2 bnf &rest resolvers
This function lets you specify the grammar using a BNF notation.
It accepts a @var{bnf} description of the grammar along with a set of
conflict resolution rules @var{resolvers}, and
returns a @emph{prec2} table.
@var{bnf} is a list of nonterminal definitions of the form
@code{(@var{nonterm} @var{rhs1} @var{rhs2} ...)} where each @var{rhs}
is a (non-empty) list of terminals (aka tokens) or non-terminals.
Not all grammars are accepted:
@itemize
@item
An @var{rhs} cannot be an empty list (an empty list is never needed,
since SMIE allows all non-terminals to match the empty string anyway).
@item
An @var{rhs} cannot have 2 consecutive non-terminals: each pair of
non-terminals needs to be separated by a terminal (aka token).
This is a fundamental limitation of operator precedence grammars.
@end itemize
Additionally, conflicts can occur:
@itemize
@item
The returned @emph{prec2} table holds constraints between pairs of tokens, and
for any given pair only one constraint can be present: T1 < T2,
T1 = T2, or T1 > T2.
@item
A token can be an @code{opener} (something similar to an open-paren),
a @code{closer} (like a close-paren), or @code{neither} of the two
(e.g. an infix operator, or an inner token like @code{"else"}).
@end itemize
Precedence conflicts can be resolved via @var{resolvers}, which
is a list of @emph{precs} tables (see @code{smie-precs->prec2}): for
each precedence conflict, if those @code{precs} tables
specify a particular constraint, then the conflict is resolved by using
this constraint instead, else a conflict is reported and one of the
conflicting constraints is picked arbitrarily and the others are
simply ignored.
@end defun
@node SMIE Grammar
@subsubsection Defining the Grammar of a Language
The usual way to define the SMIE grammar of a language is by
defining a new global variable that holds the precedence table by
giving a set of BNF rules.
For example, the grammar definition for a small Pascal-like language
could look like:
@example
@group
(require 'smie)
(defvar sample-smie-grammar
(smie-prec2->grammar
(smie-bnf->prec2
@end group
@group
'((id)
(inst ("begin" insts "end")
("if" exp "then" inst "else" inst)
(id ":=" exp)
(exp))
(insts (insts ";" insts) (inst))
(exp (exp "+" exp)
(exp "*" exp)
("(" exps ")"))
(exps (exps "," exps) (exp)))
@end group
@group
'((assoc ";"))
'((assoc ","))
'((assoc "+") (assoc "*")))))
@end group
@end example
@noindent
A few things to note:
@itemize
@item
The above grammar does not explicitly mention the syntax of function
calls: SMIE will automatically allow any sequence of sexps, such as
identifiers, balanced parentheses, or @code{begin ... end} blocks
to appear anywhere anyway.
@item
The grammar category @code{id} has no right hand side: this does not
mean that it can match only the empty string, since as mentioned any
sequence of sexps can appear anywhere anyway.
@item
Because non terminals cannot appear consecutively in the BNF grammar, it
is difficult to correctly handle tokens that act as terminators, so the
above grammar treats @code{";"} as a statement @emph{separator} instead,
which SMIE can handle very well.
@item
Separators used in sequences (such as @code{","} and @code{";"} above)
are best defined with BNF rules such as @code{(foo (foo "separator" foo) ...)}
which generate precedence conflicts which are then resolved by giving
them an explicit @code{(assoc "separator")}.
@item
The @code{("(" exps ")")} rule was not needed to pair up parens, since
SMIE will pair up any characters that are marked as having paren syntax
in the syntax table. What this rule does instead (together with the
definition of @code{exps}) is to make it clear that @code{","} should
not appear outside of parentheses.
@item
Rather than have a single @emph{precs} table to resolve conflicts, it is
preferable to have several tables, so as to let the BNF part of the
grammar specify relative precedences where possible.
@item
Unless there is a very good reason to prefer @code{left} or
@code{right}, it is usually preferable to mark operators as associative,
using @code{assoc}. For that reason @code{"+"} and @code{"*"} are
defined above as @code{assoc}, although the language defines them
formally as left associative.
@end itemize
@node SMIE Lexer
@subsubsection Defining Tokens
SMIE comes with a predefined lexical analyzer which uses syntax tables
in the following way: any sequence of characters that have word or
symbol syntax is considered a token, and so is any sequence of
characters that have punctuation syntax. This default lexer is
often a good starting point but is rarely actually correct for any given
language. For example, it will consider @code{"2,+3"} to be composed
of 3 tokens: @code{"2"}, @code{",+"}, and @code{"3"}.
To describe the lexing rules of your language to SMIE, you need
2 functions, one to fetch the next token, and another to fetch the
previous token. Those functions will usually first skip whitespace and
comments and then look at the next chunk of text to see if it
is a special token. If so it should skip the token and
return a description of this token. Usually this is simply the string
extracted from the buffer, but it can be anything you want.
For example:
@example
@group
(defvar sample-keywords-regexp
(regexp-opt '("+" "*" "," ";" ">" ">=" "<" "<=" ":=" "=")))
@end group
@group
(defun sample-smie-forward-token ()
(forward-comment (point-max))
(cond
((looking-at sample-keywords-regexp)
(goto-char (match-end 0))
(match-string-no-properties 0))
(t (buffer-substring-no-properties
(point)
(progn (skip-syntax-forward "w_")
(point))))))
@end group
@group
(defun sample-smie-backward-token ()
(forward-comment (- (point)))
(cond
((looking-back sample-keywords-regexp (- (point) 2) t)
(goto-char (match-beginning 0))
(match-string-no-properties 0))
(t (buffer-substring-no-properties
(point)
(progn (skip-syntax-backward "w_")
(point))))))
@end group
@end example
Notice how those lexers return the empty string when in front of
parentheses. This is because SMIE automatically takes care of the
parentheses defined in the syntax table. More specifically if the lexer
returns nil or an empty string, SMIE tries to handle the corresponding
text as a sexp according to syntax tables.
@node SMIE Tricks
@subsubsection Living With a Weak Parser
The parsing technique used by SMIE does not allow tokens to behave
differently in different contexts. For most programming languages, this
manifests itself by precedence conflicts when converting the
BNF grammar.
Sometimes, those conflicts can be worked around by expressing the
grammar slightly differently. For example, for Modula-2 it might seem
natural to have a BNF grammar that looks like this:
@example
...
(inst ("IF" exp "THEN" insts "ELSE" insts "END")
("CASE" exp "OF" cases "END")
...)
(cases (cases "|" cases) (caselabel ":" insts) ("ELSE" insts))
...
@end example
But this will create conflicts for @code{"ELSE"}: on the one hand, the
IF rule implies (among many other things) that @code{"ELSE" = "END"};
but on the other hand, since @code{"ELSE"} appears within @code{cases},
which appears left of @code{"END"}, we also have @code{"ELSE" > "END"}.
We can solve the conflict either by using:
@example
...
(inst ("IF" exp "THEN" insts "ELSE" insts "END")
("CASE" exp "OF" cases "END")
("CASE" exp "OF" cases "ELSE" insts "END")
...)
(cases (cases "|" cases) (caselabel ":" insts))
...
@end example
or
@example
...
(inst ("IF" exp "THEN" else "END")
("CASE" exp "OF" cases "END")
...)
(else (insts "ELSE" insts))
(cases (cases "|" cases) (caselabel ":" insts) (else))
...
@end example
Reworking the grammar to try and solve conflicts has its downsides, tho,
because SMIE assumes that the grammar reflects the logical structure of
the code, so it is preferable to keep the BNF closer to the intended
abstract syntax tree.
Other times, after careful consideration you may conclude that those
conflicts are not serious and simply resolve them via the
@var{resolvers} argument of @code{smie-bnf->prec2}. Usually this is
because the grammar is simply ambiguous: the conflict does not affect
the set of programs described by the grammar, but only the way those
programs are parsed. This is typically the case for separators and
associative infix operators, where you want to add a resolver like
@code{'((assoc "|"))}. Another case where this can happen is for the
classic @emph{dangling else} problem, where you will use @code{'((assoc
"else" "then"))}. It can also happen for cases where the conflict is
real and cannot really be resolved, but it is unlikely to pose a problem
in practice.
Finally, in many cases some conflicts will remain despite all efforts to
restructure the grammar. Do not despair: while the parser cannot be
made more clever, you can make the lexer as smart as you want. So, the
solution is then to look at the tokens involved in the conflict and to
split one of those tokens into 2 (or more) different tokens. E.g. if
the grammar needs to distinguish between two incompatible uses of the
token @code{"begin"}, make the lexer return different tokens (say
@code{"begin-fun"} and @code{"begin-plain"}) depending on which kind of
@code{"begin"} it finds. This pushes the work of distinguishing the
different cases to the lexer, which will thus have to look at the
surrounding text to find ad-hoc clues.
@node SMIE Indentation
@subsubsection Specifying Indentation Rules
Based on the provided grammar, SMIE will be able to provide automatic
indentation without any extra effort. But in practice, this default
indentation style will probably not be good enough. You will want to
tweak it in many different cases.
SMIE indentation is based on the idea that indentation rules should be
as local as possible. To this end, it relies on the idea of
@emph{virtual} indentation, which is the indentation that a particular
program point would have if it were at the beginning of a line.
Of course, if that program point is indeed at the beginning of a line,
its virtual indentation is its current indentation. But if not, then
SMIE uses the indentation algorithm to compute the virtual indentation
of that point. Now in practice, the virtual indentation of a program
point does not have to be identical to the indentation it would have if
we inserted a newline before it. To see how this works, the SMIE rule
for indentation after a @code{@{} in C does not care whether the
@code{@{} is standing on a line of its own or is at the end of the
preceding line. Instead, these different cases are handled in the
indentation rule that decides how to indent before a @code{@{}.
Another important concept is the notion of @emph{parent}: The
@emph{parent} of a token, is the head token of the nearest enclosing
syntactic construct. For example, the parent of an @code{else} is the
@code{if} to which it belongs, and the parent of an @code{if}, in turn,
is the lead token of the surrounding construct. The command
@code{backward-sexp} jumps from a token to its parent, but there are
some caveats: for @emph{openers} (tokens which start a construct, like
@code{if}), you need to start with point before the token, while for
others you need to start with point after the token.
@code{backward-sexp} stops with point before the parent token if that is
the @emph{opener} of the token of interest, and otherwise it stops with
point after the parent token.
SMIE indentation rules are specified using a function that takes two
arguments @var{method} and @var{arg} where the meaning of @var{arg} and the
expected return value depend on @var{method}.
@var{method} can be:
@itemize
@item
@code{:after}, in which case @var{arg} is a token and the function
should return the @var{offset} to use for indentation after @var{arg}.
@item
@code{:before}, in which case @var{arg} is a token and the function
should return the @var{offset} to use to indent @var{arg} itself.
@item
@code{:elem}, in which case the function should return either the offset
to use to indent function arguments (if @var{arg} is the symbol
@code{arg}) or the basic indentation step (if @var{arg} is the symbol
@code{basic}).
@item
@code{:list-intro}, in which case @var{arg} is a token and the function
should return non-@code{nil} if the token is followed by a list of
expressions (not separated by any token) rather than an expression.
@end itemize
When @var{arg} is a token, the function is called with point just before
that token. A return value of nil always means to fallback on the
default behavior, so the function should return nil for arguments it
does not expect.
@var{offset} can be:
@itemize
@item
@code{nil}: use the default indentation rule.
@item
@code{(column . @var{column})}: indent to column @var{column}.
@item
@var{number}: offset by @var{number}, relative to a base token which is
the current token for @code{:after} and its parent for @code{:before}.
@end itemize
@node SMIE Indentation Helpers
@subsubsection Helper Functions for Indentation Rules
SMIE provides various functions designed specifically for use in the
indentation rules function (several of those functions break if used in
another context). These functions all start with the prefix
@code{smie-rule-}.
@defun smie-rule-bolp
Return non-@code{nil} if the current token is the first on the line.
@end defun
@defun smie-rule-hanging-p
Return non-@code{nil} if the current token is @emph{hanging}.
A token is @emph{hanging} if it is the last token on the line
and if it is preceded by other tokens: a lone token on a line is not
hanging.
@end defun
@defun smie-rule-next-p &rest tokens
Return non-@code{nil} if the next token is among @var{tokens}.
@end defun
@defun smie-rule-prev-p &rest tokens
Return non-@code{nil} if the previous token is among @var{tokens}.
@end defun
@defun smie-rule-parent-p &rest parents
Return non-@code{nil} if the current token's parent is among @var{parents}.
@end defun
@defun smie-rule-sibling-p
Return non-nil if the current token's parent is actually a sibling.
This is the case for example when the parent of a @code{","} is just the
previous @code{","}.
@end defun
@defun smie-rule-parent &optional offset
Return the proper offset to align the current token with the parent.
If non-@code{nil}, @var{offset} should be an integer giving an
additional offset to apply.
@end defun
@defun smie-rule-separator method
Indent current token as a @emph{separator}.
By @emph{separator}, we mean here a token whose sole purpose is to
separate various elements within some enclosing syntactic construct, and
which does not have any semantic significance in itself (i.e. it would
typically not exist as a node in an abstract syntax tree).
Such a token is expected to have an associative syntax and be closely
tied to its syntactic parent. Typical examples are @code{","} in lists
of arguments (enclosed inside parentheses), or @code{";"} in sequences
of instructions (enclosed in a @code{@{...@}} or @code{begin...end}
block).
@var{method} should be the method name that was passed to
`smie-rules-function'.
@end defun
@node SMIE Indentation Example
@subsubsection Sample Indentation Rules
Here is an example of an indentation function:
@example
(eval-when-compile (require 'cl)) ;For the `case' macro.
(defun sample-smie-rules (kind token)
(case kind
(:elem (case token
(basic sample-indent-basic)))
(:after
(cond
((equal token ",") (smie-rule-separator kind))
((equal token ":=") sample-indent-basic)))
(:before
(cond
((equal token ",") (smie-rule-separator kind))
((member token '("begin" "(" "@{"))
(if (smie-rule-hanging-p) (smie-rule-parent)))
((equal token "if")
(and (not (smie-rule-bolp)) (smie-rule-prev-p "else")
(smie-rule-parent)))))))
@end example
@noindent
A few things to note:
@itemize
@item
The first case indicates the basic indentation increment to use.
If @code{sample-indent-basic} is nil, then SMIE uses the global
setting @code{smie-indent-basic}. The major mode could have set
@code{smie-indent-basic} buffer-locally instead, but that
is discouraged.
@item
The two (identical) rules for the token @code{","} make SMIE try to be
more clever when the comma separator is placed at the beginning of
lines. It tries to outdent the separator so as to align the code after
the comma; for example:
@example
x = longfunctionname (
arg1
, arg2
);
@end example
@item
The rule for indentation after @code{":="} exists because otherwise
SMIE would treat @code{":="} as an infix operator and would align the
right argument with the left one.
@item
The rule for indentation before @code{"begin"} is an example of the use
of virtual indentation: This rule is used only when @code{"begin"} is
hanging, which can happen only when @code{"begin"} is not at the
beginning of a line. So this is not used when indenting
@code{"begin"} itself but only when indenting something relative to this
@code{"begin"}. Concretely, this rule changes the indentation from:
@example
if x > 0 then begin
dosomething(x);
end
@end example
to
@example
if x > 0 then begin
dosomething(x);
end
@end example
@item
The rule for indentation before @code{"if"} is similar to the one for
@code{"begin"}, but where the purpose is to treat @code{"else if"}
as a single unit, so as to align a sequence of tests rather than indent
each test further to the right. This function does this only in the
case where the @code{"if"} is not placed on a separate line, hence the
@code{smie-rule-bolp} test.
If we know that the @code{"else"} is always aligned with its @code{"if"}
and is always at the beginning of a line, we can use a more efficient
rule:
@example
((equal token "if")
(and (not (smie-rule-bolp)) (smie-rule-prev-p "else")
(save-excursion
(sample-smie-backward-token) ;Jump before the "else".
(cons 'column (current-column)))))
@end example
The advantage of this formulation is that it reuses the indentation of
the previous @code{"else"}, rather than going all the way back to the
first @code{"if"} of the sequence.
@end itemize
@node Desktop Save Mode
@section Desktop Save Mode
@cindex desktop save mode

2
doc/lispref/text.texi
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@ -2209,7 +2209,7 @@ various commands) to indent the current line. The command
In Lisp mode, the value is the symbol @code{lisp-indent-line}; in C
mode, @code{c-indent-line}; in Fortran mode, @code{fortran-indent-line}.
The default value is @code{indent-relative}.
The default value is @code{indent-relative}. @xref{Auto-Indentation}.
@end defvar
@deffn Command indent-according-to-mode