1 @c -*- coding: us-ascii; mode: texinfo; -*-
3 @chapter Programming work
6 * Overview of LilyPond architecture::
7 * LilyPond programming languages::
8 * Programming without compiling::
11 * Debugging LilyPond::
12 * Adding or modifying features::
19 @node Overview of LilyPond architecture
20 @section Overview of LilyPond architecture
22 LilyPond processes the input file into graphical and musical output in a
23 number of stages. This process, along with the types of routines that
24 accomplish the various stages of the process, is described in this section. A
25 more complete description of the LilyPond architecture and internal program
26 execution is found in Erik Sandberg's
27 @uref{http://lilypond.org/web/images/thesis-erik-sandberg.pdf, master's
31 The first stage of LilyPond processing is @emph{parsing}. In the parsing
32 process, music expressions in LilyPond input format are converted to music
33 expressions in Scheme format. In Scheme format, a music expression is a list
34 in tree form, with nodes that indicate the relationships between various music
35 events. The LilyPond parser is written in Bison.
37 The second stage of LilyPond processing is @emph{iterating}. Iterating
38 assigns each music event to a context, which is the environment in which the
39 music will be finally engraved. The context is responsible for all further
40 processing of the music. It is during the iteration stage that contexts are
41 created as necessary to ensure that every note has a Voice type context (e.g.
42 Voice, TabVoice, DrumVoice, CueVoice, MensuralVoice, VaticanaVoice,
43 GregorianTranscriptionVoice), that the Voice type contexts exist in
44 appropriate Staff type contexts, and that parallel Staff type contexts exist
45 in StaffGroup type contexts. In addition, during the iteration stage each
46 music event is assigned a moment, or a time in the music when the event
49 Each type of music event has an associated iterator. Iterators are defined in
50 *-iterator.cc. During iteration, an
51 event's iterator is called to deliver that music event to the appropriate
54 The final stage of LilyPond processing is @emph{translation}. During
55 translation, music events are prepared for graphical or midi output. The
56 translation step is accomplished by the polymorphic base class Translator
57 through its two derived classes: Engraver (for graphical output) and
58 Performer (for midi output).
60 Translators are defined in C++ files named *-engraver.cc and *-performer.cc.
61 Much of the work of translating is handled by Scheme functions,
62 which is one of the keys to LilyPond's exceptional flexibility.
64 @sourceimage{architecture-diagram,,,png}
67 @node LilyPond programming languages
68 @section LilyPond programming languages
70 Programming in LilyPond is done in a variety of programming languages. Each
71 language is used for a specific purpose or purposes. This section describes
72 the languages used and provides links to reference manuals and tutorials for
73 the relevant language.
77 The core functionality of LilyPond is implemented in C++.
79 C++ is so ubiquitous that it is difficult to identify either a reference
80 manual or a tutorial. Programmers unfamiliar with C++ will need to spend some
81 time to learn the language before attempting to modify the C++ code.
83 The C++ code calls Scheme/GUILE through the GUILE interface, which is
85 @uref{http://www.gnu.org/software/guile/manual/html_node/index.html, GUILE
90 The LilyPond lexer is implemented in Flex, an implementation of the Unix lex
91 lexical analyser generator. Resources for Flex can be found
92 @uref{http://flex.sourceforge.net/, here}.
96 The LilyPond parser is implemented in Bison, a GNU parser generator. The
97 Bison homepage is found at @uref{http://www.gnu.org/software/bison/,
98 gnu.org}. The manual (which includes both a reference and tutorial) is
99 @uref{http://www.gnu.org/software/bison/manual/index.html, available} in a
104 GNU Make is used to control the compiling process and to build the
105 documentation and the website. GNU Make documentation is available at
106 @uref{http://www.gnu.org/software/make/manual/, the GNU website}.
108 @subsection GUILE or Scheme
110 GUILE is the dialect of Scheme that is used as LilyPond's extension language.
111 Many extensions to LilyPond are written entirely in GUILE. The
112 @uref{http://www.gnu.org/software/guile/manual/html_node/index.html,
113 GUILE Reference Manual} is available online.
115 @uref{http://mitpress.mit.edu/sicp/full-text/book/book.html, Structure and
116 Interpretation of Computer Programs}, a popular textbook used to teach
117 programming in Scheme is available in its entirety online.
119 An introduction to Guile/Scheme as used in LilyPond can be found in the
120 Learning Manual, see @rlearning{Scheme tutorial}.
124 MetaFont is used to create the music fonts used by LilyPond. A MetaFont
125 tutorial is available at @uref{http://metafont.tutorial.free.fr/, the
126 METAFONT tutorial page}.
128 @subsection PostScript
130 PostScript is used to generate graphical output. A brief PostScript tutorial
131 is @uref{http://local.wasp.uwa.edu.au/~pbourke/dataformats/postscript/,
132 available online}. The
133 @uref{http://www.adobe.com/devnet/postscript/pdfs/PLRM.pdf, PostScript Lanugage
134 Reference} is available online in PDF format.
138 Python is used for XML2ly and is used for buillding the documentation and the
141 Python documentation is available at @uref{http://www.python.org/doc/,
144 @node Programming without compiling
145 @section Programming without compiling
147 Much of the development work in LilyPond takes place by changing *.ly or
148 *.scm files. These changes can be made without compiling LilyPond. Such
149 changes are described in this section.
152 @subsection Modifying distribution files
154 Much of LilyPond is written in Scheme or LilyPond input files. These
155 files are interpreted when the program is run, rather than being compiled
156 when the program is built, and are present in all LilyPond distributions.
157 You will find .ly files in the ly/ directory and the Scheme files in the
158 scm/ directory. Both Scheme files and .ly files can be modified and
159 saved with any text editor. It's probably wise to make a backup copy of
160 your files before you modify them, although you can reinstall if the
161 files become corrupted.
163 Once you've modified the files, you can test the changes just by running
164 LilyPond on some input file. It's a good idea to create a file that
165 demonstrates the feature you're trying to add. This file will eventually
166 become a regression test and will be part of the LilyPond distribution.
168 @subsection Desired file formatting
170 Files that are part of the LilyPond distribution have Unix-style line
171 endings (LF), rather than DOS (CR+LF) or MacOS 9 and earlier (CR). Make
172 sure you use the necessary tools to ensure that Unix-style line endings are
173 preserved in the patches you create.
175 Tab characters should not be included in files for distribution. All
176 indentation should be done with spaces. Most editors have settings to
177 allow the setting of tab stops and ensuring that no tab characters are
178 included in the file.
180 Scheme files and LilyPond files should be written according to standard
181 style guidelines. Scheme file guidelines can be found at
182 @uref{http://community.schemewiki.org/?scheme-style}. Following these
183 guidelines will make your code easier to read. Both you and others that
184 work on your code will be glad you followed these guidelines.
186 For LilyPond files, you should follow the guidelines for LilyPond snippets
187 in the documentation. You can find these guidelines at
188 @ref{Texinfo introduction and usage policy}.
190 @node Finding functions
191 @section Finding functions
193 When making changes or fixing bugs in LilyPond, one of the initial
194 challenges is finding out where in the code tree the functions to
195 be modified live. With nearly 3000 files in the source tree,
196 trial-and-error searching is generally ineffective. This section
197 describes a process for finding interesting code.
199 @subsection Using the ROADMAP
201 The file ROADMAP is located in the main directory of the lilypond source.
202 ROADMAP lists all of the directories in the LilPond source tree, along
203 with a brief description of the kind of files found in each directory.
204 This can be a very helpful tool for deciding which directories to search
205 when looking for a function.
208 @subsection Using grep to search
210 Having identified a likely subdirectory to search, the grep utility can
211 be used to search for a function name. The format of the grep command is
214 grep -i functionName subdirectory/*
217 This command will search all the contents of the directory subdirectory/
218 and display every line in any of the files that contains
219 functionName. The @code{-i} option makes @command{grep} ignore
220 case -- this can be very useful if you are not yet familiar with
221 our capitalization conventions.
223 The most likely directories to grep for function names are scm/ for
224 scheme files, ly/ for lilypond input (*.ly) files, and lily/ for C++
228 @subsection Using git grep to search
230 If you have used git to obtain the source, you have access to a
231 powerful tool to search for functions. The command:
234 git grep functionName
237 will search through all of the files that are present in the git
238 repository looking for functionName. It also presents the results
239 of the search using @code{less}, so the results are displayed one page
242 @subsection Searching on the git repository at Savannah
244 You can also use the equivalent of git grep on the Savannah server.
249 Go to http://git.sv.gnu.org/gitweb/?p=lilypond.git
252 In the pulldown box that says commit, select grep.
255 Type functionName in the search box, and hit enter/return
259 This will initiate a search of the remote git repository.
268 @subsection Handling errors
270 As a general rule, you should always try to continue computations,
271 even if there is some kind of error. When the program stops, it
272 is often very hard for a user to pinpoint what part of the input
273 causes an error. Finding the culprit is much easier if there is
274 some viewable output.
276 So functions and methods do not return errorcodes, they never
277 crash, but report a programming_error and try to carry on.
279 @subsection Languages
281 C++ and Python are preferred. Python code should use PEP 8.
283 @subsection Filenames
285 Definitions of classes that are only accessed via pointers (*) or
286 references (&) shall not be included as include files.
292 ".cc" Implementation files
293 ".icc" Inline definition files
294 ".tcc" non inline Template defs
298 (setq auto-mode-alist
299 (append '(("\\.make$" . makefile-mode)
300 ("\\.cc$" . c++-mode)
301 ("\\.icc$" . c++-mode)
302 ("\\.tcc$" . c++-mode)
303 ("\\.hh$" . c++-mode)
304 ("\\.pod$" . text-mode)
309 The class Class_name is coded in @q{class-name.*}
311 @subsection Indentation
313 Standard GNU coding style is used. In emacs:
316 (add-hook 'c++-mode-hook
317 '(lambda() (c-set-style "gnu")
321 If you like using font-lock, you can also add this to your
325 (setq font-lock-maximum-decoration t)
326 (setq c++-font-lock-keywords-3
328 c++-font-lock-keywords-3
329 '(("\\b\\(a-zA-Z_?+_\\)\\b" 1 font-lock-variable-name-face) ("\\b\\(A-Z?+a-z_?+\\)\\b" 1 font-lock-type-face))
333 Some source files may not currently have proper indenting. If this
334 is the case, it is desirable to fix the improper indenting when the
335 file is modified, with the hope of continually improving the code.
337 @subsection Indenting files with emacs in script mode
339 @c email to wl@gnu.org when I get here.
341 @warning{this is pending some confirmation on -devel. July 2009 -gp}
343 Command-line script to format stuff with emacs:
347 emacs $1 -batch --eval '(indent-region (point-min) (point-max) nil)' -f save-buffer
350 (that's all on one line)
352 Save it as a shell script, then run on the file(s) you modified.
354 @subsection Indenting with vim
356 Although emacs indentation is the LilyPond standard, acceptable
357 indentation can usually be accomplished with vim. Some hints for
369 filetype plugin indent on
371 set ignorecase smartcase
374 set statusline=%F%m%r%h%w\ %{&ff}\ %Y\ [ASCII=\%03.3b]\ [HEX=\%02.2B]\ %04l,%04v\ %p%%\ [LEN=%L]
377 " Remove trailing whitespace on write
378 autocmd BufWritePre * :%s/\s\+$//e
381 With this .vimrc, files can be reindented automatically by highlihting
382 the lines to be indented in visual mode (use V to enter visual mode)
385 A scheme.vim file will help improve the indentation. This one
386 was suggested by Patrick McCarty. It should be saved in
387 ~/.vim/after/syntax/scheme.vim.
390 " Additional Guile-specific 'forms'
391 syn keyword schemeSyntax define-public define* define-safe-public
392 syn keyword schemeSyntax use-modules define-module
393 syn keyword schemeSyntax defmacro-public define-macro
394 syn keyword schemeSyntax define-markup-command
395 syn keyword schemeSyntax define-markup-list-command
396 syn keyword schemeSyntax let-keywords* lambda* define*-public
397 syn keyword schemeSyntax defmacro* defmacro*-public
399 " All of the above should influence indenting too
400 set lw+=define-public,define*,define-safe-public,use-modules,define-module
401 set lw+=defmacro-public,define-macro
402 set lw+=define-markup-command,define-markup-list-command
403 set lw+=let-keywords*,lambda*,define*-public,defmacro*,defmacro*-public
405 " These forms should not influence indenting
409 " Try to highlight all ly: procedures
410 syn match schemeFunc "ly:[^) ]\+"
413 @subsection Classes and Types
422 Member variable names end with an underscore:
431 Macro names should be written in uppercase completely.
434 @subsection Broken code
436 Do not write broken code. This includes hardwired dependencies,
437 hardwired constants, slow algorithms and obvious limitations. If
438 you can not avoid it, mark the place clearly, and add a comment
439 explaining shortcomings of the code.
441 We reject broken-in-advance on principle.
445 Variable names should be complete words, rather than abbreviations.
446 For example, it is preferred to use @code{thickness} rather than
447 @code{th} or @code{t}.
449 Multi-word variable names in C++ should have the words separated
450 by the underscore character (@q{_}).
452 Multi-word variable names in Scheme should have the words separated
457 Comments may not be needed if descriptive variable names are used
458 in the code and the logic is straightforward. However, if the
459 logic is difficult to follow, and particularly if non-obvious
460 code has been included to resolve a bug, a comment describing
461 the logic and/or the need for the non-obvious code should be included.
463 There are instances where the current code could be commented better.
464 If significant time is required to understand the code as part of
465 preparing a patch, it would be wise to add comments reflecting your
466 understanding to make future work easier.
470 Messages need to follow Localization.
473 @subsection Localization
475 This document provides some guidelines for programmers write user
476 messages. To help translations, user messages must follow
477 uniform conventions. Follow these rules when coding for LilyPond.
478 Hopefully, this can be replaced by general GNU guidelines in the
479 future. Even better would be to have an English (en_BR, en_AM)
480 guide helping programmers writing consistent messages for all GNU
483 Non-preferred messages are marked with `+'. By convention,
484 ungrammatical examples are marked with `*'. However, such ungrammatical
485 examples may still be preferred.
490 Every message to the user should be localized (and thus be marked
491 for localization). This includes warning and error messages.
494 Do not localize/gettextify:
498 `programming_error ()'s
501 `programming_warning ()'s
507 output strings (PostScript, TeX, etc.)
512 Messages to be localized must be encapsulated in `_ (STRING)' or
513 `_f (FORMAT, ...)'. E.g.:
516 warning (_ ("need music in a score"));
517 error (_f ("cannot open file: `%s'", file_name));
520 In some rare cases you may need to call `gettext ()' by hand. This
521 happens when you pre-define (a list of) string constants for later
522 use. In that case, you'll probably also need to mark these string
523 constants for translation, using `_i (STRING)'. The `_i' macro is
524 a no-op, it only serves as a marker for `xgettext'.
527 char const* messages[] = @{
528 _i ("enable debugging output"),
529 _i ("ignore lilypond version"),
536 puts (gettext (messages i));
540 See also `flower/getopt-long.cc' and `lily/main.cc'.
543 Do not use leading or trailing whitespace in messages. If you need
544 whitespace to be printed, prepend or append it to the translated
548 message ("Calculating line breaks..." + " ");
552 Error or warning messages displayed with a file name and line
553 number never start with a capital, eg,
556 foo.ly: 12: not a duration: 3
559 Messages containing a final verb, or a gerund (`-ing'-form) always
560 start with a capital. Other (simpler) messages start with a
566 Not declaring: `foo'.
570 Avoid abbreviations or short forms, use `cannot' and `do not'
571 rather than `can't' or `don't'
572 To avoid having a number of different messages for the same
573 situation, well will use quoting like this `"message: `%s'"' for all
574 strings. Numbers are not quoted:
577 _f ("cannot open file: `%s'", name_str)
578 _f ("cannot find character number: %d", i)
582 Think about translation issues. In a lot of cases, it is better to
583 translate a whole message. The english grammar must not be imposed
584 on the translator. So, instead of
587 stem at + moment.str () + does not fit in beam
593 _f ("stem at %s does not fit in beam", moment.str ())
597 Split up multi-sentence messages, whenever possible. Instead of
600 warning (_f ("out of tune! Can't find: `%s'", "Key_engraver"));
601 warning (_f ("cannot find font `%s', loading default", font_name));
607 warning (_ ("out of tune:"));
608 warning (_f ("cannot find: `%s', "Key_engraver"));
609 warning (_f ("cannot find font: `%s', font_name));
610 warning (_f ("Loading default font"));
614 If you must have multiple-sentence messages, use full punctuation.
615 Use two spaces after end of sentence punctuation. No punctuation
616 (esp. period) is used at the end of simple messages.
619 _f ("Non-matching braces in text `%s', adding braces", text)
620 _ ("Debug output disabled. Compiled with NPRINT.")
621 _f ("Huh? Not a Request: `%s'. Ignoring.", request)
625 Do not modularize too much; words frequently cannot be translated
626 without context. It is probably safe to treat most occurences of
627 words like stem, beam, crescendo as separately translatable words.
630 When translating, it is preferable to put interesting information
631 at the end of the message, rather than embedded in the middle.
632 This especially applies to frequently used messages, even if this
633 would mean sacrificing a bit of eloquency. This holds for original
634 messages too, of course.
637 en: cannot open: `foo.ly'
638 + nl: kan `foo.ly' niet openen (1)
639 kan niet openen: `foo.ly'* (2)
640 niet te openen: `foo.ly'* (3)
644 The first nl message, although grammatically and stylistically
645 correct, is not friendly for parsing by humans (even if they speak
646 dutch). I guess we would prefer something like (2) or (3).
649 Do not run make po/po-update with GNU gettext < 0.10.35
655 @node Debugging LilyPond
656 @section Debugging LilyPond
658 The most commonly used tool for debugging LilyPond is the GNU debugger
659 gdb. Use of gdb is described in this section.
661 @subsection Debugging overview
663 Using a debugger simplifies troubleshooting in at least two ways.
665 First, breakpoints can be set to pause execution at any desired point.
666 Then, when execution has paused, debugger commands can be issued to
667 explore the values of various variables or to execute functions.
669 Second, the debugger allows the display of a stack trace, which shows
670 the sequence in which functions are called and the arguments to the
671 various function calls.
674 @subsection Compiling with debugging information
676 In order to use a debugger with LilyPond, it is necessary to compile
677 LilyPond with debugging information. This is accomplished by running
678 the following commands in the main LilyPond source directory.
681 ./configure --disable-optimising
686 This will create a version of LilyPond that contains the debugging
687 information that will allow the debugger to tie the source code
688 to the compiled code.
690 You should not do @var{make install} if you want to use a debugger
691 with LilyPond. @var{make install} will strip the debugging information
692 from the LilyPond binary.
694 To set breakpoints in Scheme functions, put
697 \include "guile-debugger.ly"
700 in your input file after any scheme procedures you have defined in
701 that file. When your input file is processed, a guile prompt
702 will be displayed. At the guile prompt, you can set breakpoints with
703 the @code{break!} procedure:
706 guile> (break! my-scheme-procedure)
709 Once you have set the desired breakpoints, you exit the guile repl frame
716 When one of the scheme routines for which you have set breakpoints is
717 entered, guile will interrupt execution in a debug frame. At this point,
718 you will have access to guile debugging commands. For a listing of these
725 @subsection Typical gdb usage
727 @subsection Typical .gdbinit files
729 The behavior of gdb can be readily customized through the use of
730 @var{.gdbinit} files. A @var{.gdbinit} file is a file named
731 @var{.gdbinit} (notice the @qq{.} at the beginning of the file name)
732 that is placed in a user's home directory.
734 The @var{.gdbinit} file below is from Han-Wen. It sets breakpoints
735 for all errors and defines functions for displaying scheme objects
736 (ps), grobs (pgrob), and parsed music expressions (pmusic).
739 file lily/out/lilypond
741 b Grob::programming_error
744 print ly_display_scm($arg0)
747 print ly_display_scm($arg0->self_scm_)
748 print ly_display_scm($arg0->mutable_property_alist_)
749 print ly_display_scm($arg0->immutable_property_alist_)
750 print ly_display_scm($arg0->object_alist_)
753 print ly_display_scm($arg0->self_scm_)
754 print ly_display_scm($arg0->mutable_property_alist_)
755 print ly_display_scm($arg0->immutable_property_alist_)
759 @subsection Using Guile interactively with LilyPond
761 In order to experiment with Scheme programming in the LilyPond
762 environment, it is convenient to have a Guile interpreter that
763 has all the LilyPond modules loaded. This requires the following
766 First, define a Scheme symbol for the active module
770 #(module-define! (resolve-module '(guile-user))
771 'lilypond-module (current-module))
774 Second, place a Scheme function in the .ly file that gives an interactive Guile
781 When the .ly file is compiled, this causes the compilation to be interrupted
782 and an interactive guile prompt to appear. When the guile prompt appears,
783 the LilyPond active module must be set as the current guile module:
786 guile> (set-current-module lilypond-module)
789 Proper operation of these commands can be demonstrated by typing the name
790 of a LilyPond public scheme function to see if it's properly defined:
793 guile> fret-diagram-verbose-markup
794 #<procedure fret-diagram-verbose-markup (layout props marking-list)>
797 If the LilyPond module has not been correctly loaded, an error
798 message will be generated:
801 guile> fret-diagram-verbose-markup
802 ERROR: Unbound variable: fret-diagram-verbose-markup
803 ABORT: (unbound-variable)
806 Once the module is properly loaded, any valid LilyPond Scheme expression
807 can be entered at the interactive prompt.
809 After the investigation is complete, the interactive guile interpreter
816 The compilation of the .ly file will then continue.
818 @node Adding or modifying features
819 @section Adding or modifying features
821 When a new feature is to be added to LilyPond, it is necessary to
822 ensure that the feature is properly integrated to maintain
823 its long-term support. This section describes the steps necessary
824 for feature addition and modification.
826 @subsection Write the code
828 You should probably create a new git branch for writing the code, as that
829 will separate it from the master branch and allow you to continue
830 to work on small projects related to master.
832 Please be sure to follow the rules for programming style discussed
833 earlier in this chapter.
835 @subsection Write regression tests
837 In order to demonstrate that the code works properly, you will
838 need to write one or more regression tests. These tests are
839 typically .ly files that are found in input/regression.
841 Regression tests should be as brief as possible to demonstrate the
842 functionality of the code.
844 Regression tests should generally cover one issue per test. Several
845 short, single-issue regression tests are preferred to a single, long,
846 multiple-issue regression test.
848 Use existing regression tests as templates to demonstrate the type of
849 header information that should be included in a regression test.
851 @subsection Write convert-ly rule
853 If the modification changes the input syntax, a convert-ly rule
854 should be written to automatically update input files from older
857 convert-ly rules are found in python/convertrules.py
859 If possible, the convert-ly rule should allow automatic updating
860 of the file. In some cases, this will not be possible, so the
861 rule will simply point out to the user that the feature needs
864 @subsection Automatically update documentation, snippets, and regtests
866 convert-ly should be used to update the documentation, the snippets,
867 and the regression tests. This not only makes the necessary syntax
868 changes, it also tests the convert-ly rules.
870 The automatic updating is a three step process. First, be sure you
871 are in the top-level source directory. Then, for the
875 find Documentation/ -name '*.itely' | xargs convert-ly -e --from @qq{@var{X.Y.Z}}
879 where @var{X.Y.Z} is the version number of the last released development
882 Next, for the snippets, do:
885 find Documentation/snippets/ -name '*.ly' | xargs convert-ly -e --from @qq{@var{X.Y.Z}}
888 Finally, for the regression tests, do:
891 find input/regression/ -name '*.ly' | xargs convert-ly -e --from @qq{@var{X.Y.Z}}
895 @subsection Manually update documentation, snippets, and regtests
897 Where the convert-ly rule is not able to automatically update the inline
898 lilypond code in the documentation (i.e. if a NOT_SMART rule is used), the
899 documentation must be manually updated. The inline snippets that require
900 changing must be changed in the English version of the docs and all
901 translated versions. If the inline code is not changed in the
902 translated documentation, the old snippets will show up in the
903 English version of the documentation.
905 Where the convert-ly rule is not able to automatically update snippets
906 in Documentation/snippets/, those snippets must be manually updated.
907 Those snippets should be copied to Documentation/snippets/new. The
908 comments at the top of the snippet describing its automatice generation
909 should be removed. All translated texidoc strings should be removed.
910 The comment @qq{% begin verbatim} should be removed. The syntax of
911 the snippet should then be manually edited.
913 Where snippets in Documentation/snippets are made obsolete, the snippet
914 should be copied to Documentation/snippets/new. The comments and
915 texidoc strings should be removed as described above. Then the body
916 of the snippet should be changed to:
920 This snippet is deprecated as of version X.Y.Z and
921 will be removed from the documentation.
926 where X.Y.Z is the version number for which the convert-ly rule was
929 Update the snippet files by running:
932 scripts/auxiliar/makelsr.py
935 Where the convert-ly rule is not able to automatically update regression
936 tests, the regression tests in input/regression should be manually
939 Although it is not required, it is helpful if the developer
940 can write relevant material for inclusion in the Notation
941 Reference. If the developer does not feel qualified to write
942 the documentation, a documentation editor will be able to
943 write it from the regression tests. The text that is added to
944 or removed from the documentation should be changed only in
947 @subsection Edit changes.tely
949 An entry should be added to Documentation/changes.tely to describe
950 the feature changes to be implemented. This is especially important
951 for changes that change input file syntax.
953 Hints for changes.tely entries are given at the top of the file.
955 New entries in changes.tely go at the top of the file.
957 The changes.tely entry should be written to show how the new change
958 improves LilyPond, if possible.
960 @subsection Verify successful build
962 When the changes have been made, successful completion must be
970 When these commands complete without error, the patch is
971 considered to function successfully.
973 Developers on Windows who are unable to build LilyPond should
974 get help from a Linux or OSX developer to do the make tests.
976 @subsection Verify regression test
978 In order to avoid breaking LilyPond, it is important to verify that
979 the regression tests all succeed. This process is described in
980 @ref{Regression tests}.
982 @subsection Post patch for comments
984 For any change other than a minor change, a patch set should be
985 posted on @uref{http://codereview.appspot.com/, Rietveld} for comment.
986 This requires the use of an external package, git-cl, and an email
989 git-cl is installed by:
992 git clone git://neugierig.org/git-cl.git
995 Then, add the git-cl directory to your PATH, or create a
996 symbolic link to the git-cl and upload.py in one of your
997 PATH directories (like usr/bin). git-cl is then
998 configured by entering the command
1005 in the LilyPond git directory and answering the questions that
1006 are asked. If you do not understand the question answer with just
1009 The patch set is posted to Rietveld as follows. Ensure your changes
1010 are committed in a separate branch, which should differ from the
1011 reference branch to be used by just the changes to be uploaded.
1012 If the reference branch is to be origin/master, ensure this is
1013 up-to-date. If necessary, use git rebase to rebase the branch
1014 containing the changes to the head of origin/master. Finally,
1015 check out branch with the changes and enter the command:
1018 git cl upload <reference SHA1 ID>
1022 where <reference SHA1 ID> is the SHA1 ID of the commit to be used
1023 as a reference source for the patch. Generally, this will be the
1024 SHA1 ID of origin/master, and in that case the command
1027 git cl upload origin/master
1033 After prompting for your Google email address and password, the
1034 patch set will be posted to Rietveld.
1036 You should then announce the patch by sending
1037 an email to lilypond-devel, with a subject line
1038 starting with PATCH:, asking for comments on the patch.
1040 As revisions are made in response to comments, successive patch sets
1041 for the same issue can be uploaded by reissuing the git-cl command
1042 with the modified branch checked out.
1044 @subsection Push patch
1046 Once all the comments have been addressed, the patch can be pushed.
1048 If the author has push privileges, the author will push the patch.
1049 Otherwise, a developer with push privileges will push the patch.
1051 @subsection Closing the issues
1053 Once the patch has been pushed, all the relevant issues should be
1056 On Rietveld, the author should log in an close the issue either by
1057 using the @q{Edit Issue} link, or by clicking the circled x icon
1058 to the left of the issue name.
1060 If the changes were in response to a feature request on the Google
1061 issue tracker for LilyPond, the author should change the status to
1062 @q{Fixed_x_y_z} where the patch was fixed in version x.y.z. If
1063 the author does not have privileges to change the status, an email
1064 should be sent to bug-lilypond requesting the BugMeister to change
1067 @node Iterator tutorial
1068 @section Iterator tutorial
1070 FIXME -- this is a placeholder for a tutorial on iterators
1072 Iterators are routines written in C++ that process music expressions
1073 and sent the music events to the appropriate engravers and/or
1076 @node Engraver tutorial
1077 @section Engraver tutorial
1079 FIXME -- This is a placeholder for a tutorial on how engravers work.
1081 Engravers are C++ classes that catch music events and
1082 create the appropriate grobs for display on the page. Though the
1083 majority of engravers are responsible for the creation of a single grob,
1084 in some cases (e.g. @code{New_fingering_engraver}), several different grobs
1087 @subsection Useful methods for information processing
1089 An engraver inherits the following public methods from the Translator
1090 base class, which can be used to process listened events and acknowledged
1094 @item @code{virtual void initialize ()}
1095 @item @code{void start_translation_timestep ()}
1096 @item @code{void process_music ()}
1097 @item @code{void process_acknowledged ()}
1098 @item @code{void stop_translation_timestep ()}
1099 @item @code{virtual void finalize ()}
1102 These methods are listed in order of translation time, with
1103 @code{initialize ()} and @code{finalize ()} bookending the whole
1104 process. @code{initialize ()} can be used for one-time initialization
1105 of context properties before translation starts, whereas
1106 @code{finalize ()} is often used to tie up loose ends at the end of
1107 translation: for example, an unterminated spanner might be completed
1108 automatically or reported with a warning message.
1110 @subsection Translation process
1112 At each timestep in the music, translation proceeds by calling the
1113 following methods in turn:
1115 @code{start_translation_timestep ()} is called before any user information enters
1116 the translators, i.e., no property operations (\set, \override, etc.) or events
1117 have been processed yet.
1119 @code{process_music ()} and @code{process_acknowledged ()} are called after events
1120 have been heard, or grobs have been acknowledged. The latter tends to be used
1121 exclusively with engravers which only acknowledge grobs, whereas the former is
1122 the default method for main processing within engravers.
1124 @code{stop_translation_timestep ()} is called after all user information has been
1125 processed prior to beginning the translation for the next timestep.
1127 @subsection Preventing garbage collection for SCM member variables
1129 In certain cases, an engraver might need to ensure private Scheme variables
1130 (with type SCM) do not get swept away by Guile's garbage collector: for example,
1131 a cache of the previous key signature which must persist persist between timesteps.
1132 The method @code{virtual derived_mark () const} can be used in such cases to mark
1133 such objects as follows:
1136 Engraver_name::derived_mark ()
1138 scm_gc_mark (private_scm_member_)
1143 @subsection Listening to music events
1145 External interfaces to to the engraver are implemented by protected
1146 macros including one or more of the following:
1149 @item @code{DECLARE_TRANSLATOR_LISTENER (event_name)}
1150 @item @code{IMPLEMENT_TRANSLATOR_LISTENER (Engraver_name, event_name)}
1154 where @var{event_name} is the type of event required to provide the
1155 input the engraver needs and @var{Engraver_name} is the name of the
1158 Following declaration of a listener, the method is implemented as follows:
1161 IMPLEMENT_TRANSLATOR_LISTENER (Engraver_name, event_name)
1163 Engraver_name::listen_event_name (Stream event *event)
1165 ...body of listener method...
1169 @subsection Acknowledging grobs
1171 Some engravers also need information from grobs as they are created
1172 and as they terminate. The mechanism and methods to obtain this
1173 information are set up by the macros:
1176 @item @code{DECLARE_ACKNOWLEDGER (grob_interface)}
1177 @item @code{DECLARE_END_ACKNOWLEDGER (grob_interface)}
1180 where @var{grob_interface} is an interface supported by the
1181 grob(s) which should be acknowledged. For example, the following
1182 code would declare acknowledgers for a @code{NoteHead} grob (via the
1183 @code{note-head-interface}) and any grobs which support the
1184 @code{side-position-interface}:
1187 @code{DECLARE_ACKNOWLEDGER (note_head)}
1188 @code{DECLARE_ACKNOWLEDGER (side_position)}
1191 The @code{DECLARE_END_ACKNOWLEDGER ()} macro sets up a spanner-specific
1192 acknowledger which will be called whenever a spanner ends.
1194 Following declaration of an acknowledger, the method is coded as follows:
1198 Engraver_name::acknowledge_interface_name (Grob_info info)
1200 ...body of acknowledger method...
1204 @subsection Engraver declaration/documentation
1206 An engraver must have a public macro
1209 @item @code{TRANSLATOR_DECLARATIONS (Engraver_name)}
1213 where @code{Engraver_name} is the name of the engraver. This
1214 defines the common variables and methods used by every engraver.
1216 At the end of the engraver file, one or both of the following
1217 macros are generally called to document the engraver in the
1218 Internals Reference:
1221 @item @code{ADD_ACKNOWLEDGER (Engraver_name, grob_interface)}
1222 @item @code{ADD_TRANSLATOR (Engraver_name, Engraver_doc,
1223 Engraver_creates, Engraver_reads, Engraver_writes)}
1227 where @code{Engraver_name} is the name of the engraver, @code{grob_interface}
1228 is the name of the interface that will be acknowledged,
1229 @code{Engraver_doc} is a docstring for the engraver,
1230 @code{Engraver_creates} is the set of grobs created by the engraver,
1231 @code{Engraver_reads} is the set of properties read by the engraver,
1232 and @code{Engraver_writes} is the set of properties written by
1235 @node Callback tutorial
1236 @section Callback tutorial
1238 FIXME -- This is a placeholder for a tutorial on callback functions.
1240 @node LilyPond scoping
1241 @section LilyPond scoping
1243 The Lilypond language has a concept of scoping, ie you can do
1249 (display (+ foo 2)))
1252 @noindent with @code{\paper}, @code{\midi} and @code{\header} being
1253 nested scope inside the .ly file-level scope. @w{@code{foo = 1}} is
1254 translated in to a scheme variable definition.
1256 This implemented using modules, with each scope being an anonymous
1257 module that imports its enclosing scope's module.
1259 The reason to put some functions (@qq{builtin}) outside the .ly level,
1267 we want to reuse the built-in definitions, without changes
1268 effected in a.ly leaking into the processing of b.ly.
1270 Maintaining this scoping when one .ly file can be included in another
1271 .ly file can be challenging. A @code{define-public-toplevel} macro
1272 has been created in order to handle a difficulty caused by the modules
1273 being not the same when a .ly file is included into another.
1274 This provided a way to define all markup commands in the same module.
1275 At this time, we have found no easier way to define a function in a given
1276 module (not the current one) than to define this macro.
1278 With this architecture, the guile module system is not bypassed:
1279 module-define!, module-export! and module-ref are all guile module
1282 A second reason for using this current architecture is to avoid memory
1283 leaks that could occur when running multiple files if toplevel
1284 functions were registered permanently.