1 @c -*- coding: utf-8; mode: texinfo; -*-
3 @chapter Programming work
6 * Overview of LilyPond architecture::
7 * LilyPond programming languages::
8 * Programming without compiling::
11 * Debugging LilyPond::
12 * Tracing object relationships::
13 * Adding or modifying features::
18 * LilyPond miscellany::
21 @node Overview of LilyPond architecture
22 @section Overview of LilyPond architecture
24 LilyPond processes the input file into graphical and musical output in a
25 number of stages. This process, along with the types of routines that
26 accomplish the various stages of the process, is described in this section. A
27 more complete description of the LilyPond architecture and internal program
28 execution is found in Erik Sandberg's
29 @uref{http://lilypond.org/web/images/thesis-erik-sandberg.pdf, master's
32 The first stage of LilyPond processing is @emph{parsing}. In the parsing
33 process, music expressions in LilyPond input format are converted to music
34 expressions in Scheme format. In Scheme format, a music expression is a list
35 in tree form, with nodes that indicate the relationships between various music
36 events. The LilyPond parser is written in Bison.
38 The second stage of LilyPond processing is @emph{iterating}. Iterating
39 assigns each music event to a context, which is the environment in which the
40 music will be finally engraved. The context is responsible for all further
41 processing of the music. It is during the iteration stage that contexts are
42 created as necessary to ensure that every note has a Voice type context (e.g.
43 Voice, TabVoice, DrumVoice, CueVoice, MensuralVoice, VaticanaVoice,
44 GregorianTranscriptionVoice), that the Voice type contexts exist in
45 appropriate Staff type contexts, and that parallel Staff type contexts exist
46 in StaffGroup type contexts. In addition, during the iteration stage each
47 music event is assigned a moment, or a time in the music when the event
50 Each type of music event has an associated iterator. Iterators are defined in
51 *-iterator.cc. During iteration, an
52 event's iterator is called to deliver that music event to the appropriate
55 The final stage of LilyPond processing is @emph{translation}. During
56 translation, music events are prepared for graphical or midi output. The
57 translation step is accomplished by the polymorphic base class Translator
58 through its two derived classes: Engraver (for graphical output) and
59 Performer (for midi output).
61 Translators are defined in C++ files named *-engraver.cc and *-performer.cc.
62 Much of the work of translating is handled by Scheme functions,
63 which is one of the keys to LilyPond's exceptional flexibility.
65 @sourceimage{architecture-diagram,,,png}
68 @node LilyPond programming languages
69 @section LilyPond programming languages
71 Programming in LilyPond is done in a variety of programming languages. Each
72 language is used for a specific purpose or purposes. This section describes
73 the languages used and provides links to reference manuals and tutorials for
74 the relevant language.
78 The core functionality of LilyPond is implemented in C++.
80 C++ is so ubiquitous that it is difficult to identify either a reference
81 manual or a tutorial. Programmers unfamiliar with C++ will need to spend some
82 time to learn the language before attempting to modify the C++ code.
84 The C++ code calls Scheme/GUILE through the GUILE interface, which is
86 @uref{http://www.gnu.org/software/guile/manual/html_node/index.html, GUILE
91 The LilyPond lexer is implemented in Flex, an implementation of the Unix lex
92 lexical analyser generator. Resources for Flex can be found
93 @uref{http://flex.sourceforge.net/, here}.
97 The LilyPond parser is implemented in Bison, a GNU parser generator. The
98 Bison homepage is found at @uref{http://www.gnu.org/software/bison/,
99 gnu.org}. The manual (which includes both a reference and tutorial) is
100 @uref{http://www.gnu.org/software/bison/manual/index.html, available} in a
105 GNU Make is used to control the compiling process and to build the
106 documentation and the website. GNU Make documentation is available at
107 @uref{http://www.gnu.org/software/make/manual/, the GNU website}.
109 @subsection GUILE or Scheme
111 GUILE is the dialect of Scheme that is used as LilyPond's extension language.
112 Many extensions to LilyPond are written entirely in GUILE. The
113 @uref{http://www.gnu.org/software/guile/manual/html_node/index.html,
114 GUILE Reference Manual} is available online.
116 @uref{http://mitpress.mit.edu/sicp/full-text/book/book.html, Structure and
117 Interpretation of Computer Programs}, a popular textbook used to teach
118 programming in Scheme is available in its entirety online.
120 An introduction to Guile/Scheme as used in LilyPond can be found in the
121 @rextend{Scheme tutorial}.
125 MetaFont is used to create the music fonts used by LilyPond. A MetaFont
126 tutorial is available at @uref{http://metafont.tutorial.free.fr/, the
127 METAFONT tutorial page}.
129 @subsection PostScript
131 PostScript is used to generate graphical output. A brief PostScript tutorial
132 is @uref{http://local.wasp.uwa.edu.au/~pbourke/dataformats/postscript/,
133 available online}. The
134 @uref{http://www.adobe.com/devnet/postscript/pdfs/PLRM.pdf, PostScript Lanugage
135 Reference} is available online in PDF format.
139 Python is used for XML2ly and is used for buillding the documentation and the
142 Python documentation is available at @uref{http://www.python.org/doc/,
145 @node Programming without compiling
146 @section Programming without compiling
148 Much of the development work in LilyPond takes place by changing *.ly or
149 *.scm files. These changes can be made without compiling LilyPond. Such
150 changes are described in this section.
153 @subsection Modifying distribution files
155 Much of LilyPond is written in Scheme or LilyPond input files. These
156 files are interpreted when the program is run, rather than being compiled
157 when the program is built, and are present in all LilyPond distributions.
158 You will find .ly files in the ly/ directory and the Scheme files in the
159 scm/ directory. Both Scheme files and .ly files can be modified and
160 saved with any text editor. It's probably wise to make a backup copy of
161 your files before you modify them, although you can reinstall if the
162 files become corrupted.
164 Once you've modified the files, you can test the changes just by running
165 LilyPond on some input file. It's a good idea to create a file that
166 demonstrates the feature you're trying to add. This file will eventually
167 become a regression test and will be part of the LilyPond distribution.
169 @subsection Desired file formatting
171 Files that are part of the LilyPond distribution have Unix-style line
172 endings (LF), rather than DOS (CR+LF) or MacOS 9 and earlier (CR). Make
173 sure you use the necessary tools to ensure that Unix-style line endings are
174 preserved in the patches you create.
176 Tab characters should not be included in files for distribution. All
177 indentation should be done with spaces. Most editors have settings to
178 allow the setting of tab stops and ensuring that no tab characters are
179 included in the file.
181 Scheme files and LilyPond files should be written according to standard
182 style guidelines. Scheme file guidelines can be found at
183 @uref{http://community.schemewiki.org/?scheme-style}. Following these
184 guidelines will make your code easier to read. Both you and others that
185 work on your code will be glad you followed these guidelines.
187 For LilyPond files, you should follow the guidelines for LilyPond snippets
188 in the documentation. You can find these guidelines at
189 @ref{Texinfo introduction and usage policy}.
191 @node Finding functions
192 @section Finding functions
194 When making changes or fixing bugs in LilyPond, one of the initial
195 challenges is finding out where in the code tree the functions to
196 be modified live. With nearly 3000 files in the source tree,
197 trial-and-error searching is generally ineffective. This section
198 describes a process for finding interesting code.
200 @subsection Using the ROADMAP
202 The file ROADMAP is located in the main directory of the lilypond source.
203 ROADMAP lists all of the directories in the LilPond source tree, along
204 with a brief description of the kind of files found in each directory.
205 This can be a very helpful tool for deciding which directories to search
206 when looking for a function.
209 @subsection Using grep to search
211 Having identified a likely subdirectory to search, the grep utility can
212 be used to search for a function name. The format of the grep command is
215 grep -i functionName subdirectory/*
218 This command will search all the contents of the directory subdirectory/
219 and display every line in any of the files that contains
220 functionName. The @code{-i} option makes @command{grep} ignore
221 case -- this can be very useful if you are not yet familiar with
222 our capitalization conventions.
224 The most likely directories to grep for function names are scm/ for
225 scheme files, ly/ for lilypond input (*.ly) files, and lily/ for C++
229 @subsection Using git grep to search
231 If you have used git to obtain the source, you have access to a
232 powerful tool to search for functions. The command:
235 git grep functionName
238 will search through all of the files that are present in the git
239 repository looking for functionName. It also presents the results
240 of the search using @code{less}, so the results are displayed one page
243 @subsection Searching on the git repository at Savannah
245 You can also use the equivalent of git grep on the Savannah server.
250 Go to http://git.sv.gnu.org/gitweb/?p=lilypond.git
253 In the pulldown box that says commit, select grep.
256 Type functionName in the search box, and hit enter/return
260 This will initiate a search of the remote git repository.
269 @subsection Handling errors
271 As a general rule, you should always try to continue computations,
272 even if there is some kind of error. When the program stops, it
273 is often very hard for a user to pinpoint what part of the input
274 causes an error. Finding the culprit is much easier if there is
275 some viewable output.
277 So functions and methods do not return errorcodes, they never
278 crash, but report a programming_error and try to carry on.
280 @subsection Languages
282 C++ and Python are preferred. Python code should use PEP 8.
284 @subsection Filenames
286 Definitions of classes that are only accessed via pointers (*) or
287 references (&) shall not be included as include files.
293 ".cc" Implementation files
294 ".icc" Inline definition files
295 ".tcc" non inline Template defs
299 (setq auto-mode-alist
300 (append '(("\\.make$" . makefile-mode)
301 ("\\.cc$" . c++-mode)
302 ("\\.icc$" . c++-mode)
303 ("\\.tcc$" . c++-mode)
304 ("\\.hh$" . c++-mode)
305 ("\\.pod$" . text-mode)
310 The class Class_name is coded in @q{class-name.*}
312 @subsection Indentation
314 Standard GNU coding style is used. In emacs:
317 (add-hook 'c++-mode-hook
318 '(lambda() (c-set-style "gnu")
322 If you like using font-lock, you can also add this to your
326 (setq font-lock-maximum-decoration t)
327 (setq c++-font-lock-keywords-3
329 c++-font-lock-keywords-3
330 '(("\\b\\(a-zA-Z_?+_\\)\\b" 1 font-lock-variable-name-face) ("\\b\\(A-Z?+a-z_?+\\)\\b" 1 font-lock-type-face))
334 Some source files may not currently have proper indenting. If this
335 is the case, it is desirable to fix the improper indenting when the
336 file is modified, with the hope of continually improving the code.
338 @subsection Indenting files with emacs in script mode
340 @c email to wl@gnu.org when I get here.
342 @warning{this is pending some confirmation on -devel. July 2009 -gp}
344 Command-line script to format stuff with emacs:
348 emacs $1 -batch --eval '(indent-region (point-min) (point-max) nil)' -f save-buffer
351 (that's all on one line)
353 Save it as a shell script, then run on the file(s) you modified.
355 @subsection Indenting with vim
357 Although emacs indentation is the LilyPond standard, acceptable
358 indentation can usually be accomplished with vim. Some hints for
370 filetype plugin indent on
372 set ignorecase smartcase
375 set statusline=%F%m%r%h%w\ %{&ff}\ %Y\ [ASCII=\%03.3b]\ [HEX=\%02.2B]\ %04l,%04v\ %p%%\ [LEN=%L]
378 " Remove trailing whitespace on write
379 autocmd BufWritePre * :%s/\s\+$//e
382 With this .vimrc, files can be reindented automatically by highlihting
383 the lines to be indented in visual mode (use V to enter visual mode)
386 A scheme.vim file will help improve the indentation. This one
387 was suggested by Patrick McCarty. It should be saved in
388 ~/.vim/after/syntax/scheme.vim.
391 " Additional Guile-specific 'forms'
392 syn keyword schemeSyntax define-public define* define-safe-public
393 syn keyword schemeSyntax use-modules define-module
394 syn keyword schemeSyntax defmacro-public define-macro
395 syn keyword schemeSyntax define-markup-command
396 syn keyword schemeSyntax define-markup-list-command
397 syn keyword schemeSyntax let-keywords* lambda* define*-public
398 syn keyword schemeSyntax defmacro* defmacro*-public
400 " All of the above should influence indenting too
401 set lw+=define-public,define*,define-safe-public,use-modules,define-module
402 set lw+=defmacro-public,define-macro
403 set lw+=define-markup-command,define-markup-list-command
404 set lw+=let-keywords*,lambda*,define*-public,defmacro*,defmacro*-public
406 " These forms should not influence indenting
410 " Try to highlight all ly: procedures
411 syn match schemeFunc "ly:[^) ]\+"
414 @subsection Classes and Types
423 Member variable names end with an underscore:
432 Macro names should be written in uppercase completely.
435 @subsection Broken code
437 Do not write broken code. This includes hardwired dependencies,
438 hardwired constants, slow algorithms and obvious limitations. If
439 you can not avoid it, mark the place clearly, and add a comment
440 explaining shortcomings of the code.
442 We reject broken-in-advance on principle.
446 Variable names should be complete words, rather than abbreviations.
447 For example, it is preferred to use @code{thickness} rather than
448 @code{th} or @code{t}.
450 Multi-word variable names in C++ should have the words separated
451 by the underscore character (@q{_}).
453 Multi-word variable names in Scheme should have the words separated
458 Comments may not be needed if descriptive variable names are used
459 in the code and the logic is straightforward. However, if the
460 logic is difficult to follow, and particularly if non-obvious
461 code has been included to resolve a bug, a comment describing
462 the logic and/or the need for the non-obvious code should be included.
464 There are instances where the current code could be commented better.
465 If significant time is required to understand the code as part of
466 preparing a patch, it would be wise to add comments reflecting your
467 understanding to make future work easier.
471 Messages need to follow Localization.
474 @subsection Localization
476 This document provides some guidelines for programmers write user
477 messages. To help translations, user messages must follow
478 uniform conventions. Follow these rules when coding for LilyPond.
479 Hopefully, this can be replaced by general GNU guidelines in the
480 future. Even better would be to have an English (en_BR, en_AM)
481 guide helping programmers writing consistent messages for all GNU
484 Non-preferred messages are marked with `+'. By convention,
485 ungrammatical examples are marked with `*'. However, such ungrammatical
486 examples may still be preferred.
491 Every message to the user should be localized (and thus be marked
492 for localization). This includes warning and error messages.
495 Do not localize/gettextify:
499 `programming_error ()'s
502 `programming_warning ()'s
508 output strings (PostScript, TeX, etc.)
513 Messages to be localized must be encapsulated in `_ (STRING)' or
514 `_f (FORMAT, ...)'. E.g.:
517 warning (_ ("need music in a score"));
518 error (_f ("cannot open file: `%s'", file_name));
521 In some rare cases you may need to call `gettext ()' by hand. This
522 happens when you pre-define (a list of) string constants for later
523 use. In that case, you'll probably also need to mark these string
524 constants for translation, using `_i (STRING)'. The `_i' macro is
525 a no-op, it only serves as a marker for `xgettext'.
528 char const* messages[] = @{
529 _i ("enable debugging output"),
530 _i ("ignore lilypond version"),
537 puts (gettext (messages i));
541 See also `flower/getopt-long.cc' and `lily/main.cc'.
544 Do not use leading or trailing whitespace in messages. If you need
545 whitespace to be printed, prepend or append it to the translated
549 message ("Calculating line breaks..." + " ");
553 Error or warning messages displayed with a file name and line
554 number never start with a capital, eg,
557 foo.ly: 12: not a duration: 3
560 Messages containing a final verb, or a gerund (`-ing'-form) always
561 start with a capital. Other (simpler) messages start with a
567 Not declaring: `foo'.
571 Avoid abbreviations or short forms, use `cannot' and `do not'
572 rather than `can't' or `don't'
573 To avoid having a number of different messages for the same
574 situation, well will use quoting like this `"message: `%s'"' for all
575 strings. Numbers are not quoted:
578 _f ("cannot open file: `%s'", name_str)
579 _f ("cannot find character number: %d", i)
583 Think about translation issues. In a lot of cases, it is better to
584 translate a whole message. The english grammar must not be imposed
585 on the translator. So, instead of
588 stem at + moment.str () + does not fit in beam
594 _f ("stem at %s does not fit in beam", moment.str ())
598 Split up multi-sentence messages, whenever possible. Instead of
601 warning (_f ("out of tune! Can't find: `%s'", "Key_engraver"));
602 warning (_f ("cannot find font `%s', loading default", font_name));
608 warning (_ ("out of tune:"));
609 warning (_f ("cannot find: `%s', "Key_engraver"));
610 warning (_f ("cannot find font: `%s', font_name));
611 warning (_f ("Loading default font"));
615 If you must have multiple-sentence messages, use full punctuation.
616 Use two spaces after end of sentence punctuation. No punctuation
617 (esp. period) is used at the end of simple messages.
620 _f ("Non-matching braces in text `%s', adding braces", text)
621 _ ("Debug output disabled. Compiled with NPRINT.")
622 _f ("Huh? Not a Request: `%s'. Ignoring.", request)
626 Do not modularize too much; words frequently cannot be translated
627 without context. It is probably safe to treat most occurences of
628 words like stem, beam, crescendo as separately translatable words.
631 When translating, it is preferable to put interesting information
632 at the end of the message, rather than embedded in the middle.
633 This especially applies to frequently used messages, even if this
634 would mean sacrificing a bit of eloquency. This holds for original
635 messages too, of course.
638 en: cannot open: `foo.ly'
639 + nl: kan `foo.ly' niet openen (1)
640 kan niet openen: `foo.ly'* (2)
641 niet te openen: `foo.ly'* (3)
645 The first nl message, although grammatically and stylistically
646 correct, is not friendly for parsing by humans (even if they speak
647 dutch). I guess we would prefer something like (2) or (3).
650 Do not run make po/po-update with GNU gettext < 0.10.35
656 @node Debugging LilyPond
657 @section Debugging LilyPond
659 The most commonly used tool for debugging LilyPond is the GNU
660 debugger gdb. The gdb tool is used for investigating and debugging
661 core Lilypond code written in C++. Another tool is available for
662 debugging Scheme code using the Guile debugger. This section
663 describes how to use both gdb and the Guile Debugger.
666 * Debugging overview::
667 * Debugging C++ code::
668 * Debugging Scheme code::
671 @node Debugging overview
672 @subsection Debugging overview
674 Using a debugger simplifies troubleshooting in at least two ways.
676 First, breakpoints can be set to pause execution at any desired point.
677 Then, when execution has paused, debugger commands can be issued to
678 explore the values of various variables or to execute functions.
680 Second, the debugger can display a stack trace, which shows the
681 sequence in which functions have been called and the arguments
682 passed to the called functions.
684 @node Debugging C++ code
685 @subsection Debugging C++ code
687 The GNU debugger, gdb, is the principal tool for debugging C++ code.
689 @unnumberedsubsubsec Compiling LilyPond for use with gdb
691 In order to use gdb with LilyPond, it is necessary to compile
692 LilyPond with debugging information. This is accomplished by running
693 the following commands in the main LilyPond source directory.
696 ./configure --disable-optimising
700 This will create a version of LilyPond containing debugging
701 information that will allow the debugger to tie the source code
702 to the compiled code.
704 You should not do @var{make install} if you want to use a debugger
705 with LilyPond. The @var{make install} command will strip debugging
706 information from the LilyPond binary.
708 @unnumberedsubsubsec Typical gdb usage
710 Once you have compiled the Lilypond image with the necessary
711 debugging information it will have been written to a location in a
712 subfolder of your current working directory:
718 This is important as you will need to let gdb know where to find the
719 image containing the symbol tables. You can invoke gdb from the
726 This loads the LilyPond symbol tables into gdb. Then, to run
727 LilyPond on @code{test.ly} under the debugger, enter
735 As an alternative to running gdb at the command line you may try
736 a graphical interface to gdb such as ddd
742 You can also use sets of standard gdb commands stored in a .gdbinit
743 file (see next section).
745 @unnumberedsubsubsec Typical .gdbinit files
747 The behavior of gdb can be readily customized through the use of a
748 @var{.gdbinit} file. A @var{.gdbinit} file is a file named
749 @var{.gdbinit} (notice the @qq{.} at the beginning of the file name)
750 that is placed in a user's home directory.
752 The @var{.gdbinit} file below is from Han-Wen. It sets breakpoints
753 for all errors and defines functions for displaying scheme objects
754 (ps), grobs (pgrob), and parsed music expressions (pmusic).
757 file lily/out/lilypond
759 b Grob::programming_error
762 print ly_display_scm($arg0)
765 print ly_display_scm($arg0->self_scm_)
766 print ly_display_scm($arg0->mutable_property_alist_)
767 print ly_display_scm($arg0->immutable_property_alist_)
768 print ly_display_scm($arg0->object_alist_)
771 print ly_display_scm($arg0->self_scm_)
772 print ly_display_scm($arg0->mutable_property_alist_)
773 print ly_display_scm($arg0->immutable_property_alist_)
777 @node Debugging Scheme code
778 @subsection Debugging Scheme code
780 Scheme code can be developed using the Guile command line
781 interpreter @code{top-repl}. You can either investigate
782 interactively using just Guile or you can use the debugging
783 tools available within Guile.
785 @unnumberedsubsubsec Using Guile interactively with LilyPond
787 In order to experiment with Scheme programming in the LilyPond
788 environment, it is necessary to have a Guile interpreter that
789 has all the LilyPond modules loaded. This requires the following
792 First, define a Scheme symbol for the active module in the .ly file:
795 #(module-define! (resolve-module '(guile-user))
796 'lilypond-module (current-module))
799 Now place a Scheme function in the .ly file that gives an
800 interactive Guile prompt:
806 When the .ly file is compiled, this causes the compilation to be
807 interrupted and an interactive guile prompt to appear. Once the
808 guile prompt appears, the LilyPond active module must be set as the
809 current guile module:
812 guile> (set-current-module lilypond-module)
815 You can demonstrate these commands are operating properly by typing the name
816 of a LilyPond public scheme function to check it has been defined:
819 guile> fret-diagram-verbose-markup
820 #<procedure fret-diagram-verbose-markup (layout props marking-list)>
823 If the LilyPond module has not been correctly loaded, an error
824 message will be generated:
827 guile> fret-diagram-verbose-markup
828 ERROR: Unbound variable: fret-diagram-verbose-markup
829 ABORT: (unbound-variable)
832 Once the module is properly loaded, any valid LilyPond Scheme
833 expression can be entered at the interactive prompt.
835 After the investigation is complete, the interactive guile
836 interpreter can be exited:
842 The compilation of the .ly file will then continue.
844 @unnumberedsubsubsec Using the Guile debugger
846 To set breakpoints and/or enable tracing in Scheme functions, put
849 \include "guile-debugger.ly"
852 in your input file after any scheme procedures you have defined in
853 that file. This will invoke the Guile command-line after having set
854 up the environment for the debug command-line. When your input file
855 is processed, a guile prompt will be displayed. You may now enter
856 commands to set up breakpoints and enable tracing by the Guile debugger.
858 @unnumberedsubsubsec Using breakpoints
860 At the guile prompt, you can set breakpoints with
861 the @code{set-break!} procedure:
864 guile> (set-break! my-scheme-procedure)
867 Once you have set the desired breakpoints, you exit the guile repl frame
874 Then, when one of the scheme routines for which you have set
875 breakpoints is entered, guile will interrupt execution in a debug
876 frame. At this point you will have access to Guile debugging
877 commands. For a listing of these commands, type:
883 Alternatively you may code the breakpoints in your Lilypond source
884 file using a command such as:
887 #(set-break! my-scheme-procedure)
890 immediately after the @code{\include} statement. In this case the
891 breakpoint will be set straight after you enter the @code{(quit)}
892 command at the guile prompt.
894 Embedding breakpoint commands like this is particularly useful if
895 you want to look at how the Scheme procedures in the @var{.scm}
896 files supplied with LilyPond work. To do this, edit the file in
897 the relevant directory to add this line near the top:
900 (use-modules (scm guile-debugger))
903 Now you can set a breakpoint after the procedure you are interested
904 in has been declared. For example, if you are working on routines
905 called by @var{print-book-with} in @var{lily-library.scm}:
908 (define (print-book-with parser book process-procedure)
909 (let* ((paper (ly:parser-lookup parser '$defaultpaper))
910 (layout (ly:parser-lookup parser '$defaultlayout))
911 (outfile-name (get-outfile-name parser)))
912 (process-procedure book paper layout outfile-name)))
914 (define-public (print-book-with-defaults parser book)
915 (print-book-with parser book ly:book-process))
917 (define-public (print-book-with-defaults-as-systems parser book)
918 (print-book-with parser book ly:book-process-to-systems))
922 At this point in the code you could add this to set a breakpoint at
926 (set-break! print-book-with)
929 @unnumberedsubsubsec Tracing procedure calls and evaluator steps
931 Two forms of trace are available:
934 (set-trace-call! my-scheme-procedure)
940 (set-trace-subtree! my-scheme-procedure)
943 @code{set-trace-call!} causes Scheme to log a line to the standard
944 output to show when the procedure is called and when it exits.
946 @code{set-trace-subtree!} traces every step the Scheme evaluator
947 performs in evaluating the procedure.
949 @node Tracing object relationships
950 @section Tracing object relationships
952 Understanding the LilyPond source often boils down to figuring out what
953 is happening to the Grobs. Where (and why) are they being created,
954 modified and destroyed? Tracing Lily through a debugger in order to
955 identify these relationships can be time-consuming and tedious.
957 In order to simplify this process, a facility has been added to
958 display the grobs that are created and the properties that are set
959 and modified. Although it can be complex to get set up, once set up
960 it easily provides detailed information about the life of grobs
961 in the form of a network graph.
963 Each of the steps necessary to use the graphviz utility
968 @item Installing graphviz
970 In order to create the graph of the object relationships, it is
971 first necessary to install Graphviz. graphviz is available for a
972 number of different platforms:
975 @uref{http://www.graphviz.org/Download..php}
978 @item Modifying config.make
980 In order for the Graphviz tool to work, config.make must be modified.
981 It is probably a good idea to first save a copy of config.make under
982 a different name. Then, edit config.make by removing every occurence
985 @item Rebuilding LilyPond
987 The executable code of LilyPond must be rebuilt from scratch:
990 make -C lily clean && make -C lily
993 @item Create a graphviz-compatible .ly file
995 In order to use the graphviz utility, the .ly file must include
996 @file{ly/graphviz-init.ly}, and should then specify the
997 grobs and symbols that should be tracked. An example of this
998 is found in @file{input/regression/graphviz.ly}.
1000 @item Run lilypond with output sent to a log file
1002 The Graphviz data is sent to stderr by lilypond, so it is
1003 necessary to redirect stderr to a logfile:
1006 lilypond graphviz.ly 2> graphviz.log
1009 @item Edit the logfile
1011 The logfile has standard lilypond output, as well as the Graphviz
1012 output data. Delete everything from the beginning of the file
1013 up to but not including the first occurence of @code{digraph}.
1015 @item Process the logfile with @code{dot}
1017 The directed graph is created from the log file with the program
1021 dot -Tpdf graphviz.log > graphviz.pdf
1026 The pdf file can then be viewed with any pdf viewer.
1028 When compiled without @code{-DNDEBUG}, lilypond may run slower
1029 than normal. The original configuration can be restored by either
1030 renaming the saved copy of @code{config.make} or rerunning
1031 @code{configure}. Then rebuild lilypond with
1034 make -C lily clean && make -C lily
1038 @node Adding or modifying features
1039 @section Adding or modifying features
1041 When a new feature is to be added to LilyPond, it is necessary to
1042 ensure that the feature is properly integrated to maintain
1043 its long-term support. This section describes the steps necessary
1044 for feature addition and modification.
1046 @subsection Write the code
1048 You should probably create a new git branch for writing the code, as that
1049 will separate it from the master branch and allow you to continue
1050 to work on small projects related to master.
1052 Please be sure to follow the rules for programming style discussed
1053 earlier in this chapter.
1055 @subsection Write regression tests
1057 In order to demonstrate that the code works properly, you will
1058 need to write one or more regression tests. These tests are
1059 typically .ly files that are found in input/regression.
1061 Regression tests should be as brief as possible to demonstrate the
1062 functionality of the code.
1064 Regression tests should generally cover one issue per test. Several
1065 short, single-issue regression tests are preferred to a single, long,
1066 multiple-issue regression test.
1068 Use existing regression tests as templates to demonstrate the type of
1069 header information that should be included in a regression test.
1071 @subsection Write convert-ly rule
1073 If the modification changes the input syntax, a convert-ly rule
1074 should be written to automatically update input files from older
1077 convert-ly rules are found in python/convertrules.py
1079 If possible, the convert-ly rule should allow automatic updating
1080 of the file. In some cases, this will not be possible, so the
1081 rule will simply point out to the user that the feature needs
1084 @subsection Automatically update documentation, snippets, and regtests
1086 convert-ly should be used to update the documentation, the snippets,
1087 and the regression tests. This not only makes the necessary syntax
1088 changes, it also tests the convert-ly rules.
1090 The automatic updating is a three step process. First, be sure you
1091 are in the top-level source directory. Then, for the
1095 find Documentation/ -name '*.itely' | xargs convert-ly -e --from @qq{@var{X.Y.Z}}
1099 where @var{X.Y.Z} is the version number of the last released development
1102 Next, for the snippets, do:
1105 find Documentation/snippets/ -name '*.ly' | xargs convert-ly -e --from @qq{@var{X.Y.Z}}
1108 Finally, for the regression tests, do:
1111 find input/regression/ -name '*.ly' | xargs convert-ly -e --from @qq{@var{X.Y.Z}}
1115 @subsection Manually update documentation, snippets, and regtests
1117 Where the convert-ly rule is not able to automatically update the inline
1118 lilypond code in the documentation (i.e. if a NOT_SMART rule is used), the
1119 documentation must be manually updated. The inline snippets that require
1120 changing must be changed in the English version of the docs and all
1121 translated versions. If the inline code is not changed in the
1122 translated documentation, the old snippets will show up in the
1123 English version of the documentation.
1125 Where the convert-ly rule is not able to automatically update snippets
1126 in Documentation/snippets/, those snippets must be manually updated.
1127 Those snippets should be copied to Documentation/snippets/new. The
1128 comments at the top of the snippet describing its automatice generation
1129 should be removed. All translated texidoc strings should be removed.
1130 The comment @qq{% begin verbatim} should be removed. The syntax of
1131 the snippet should then be manually edited.
1133 Where snippets in Documentation/snippets are made obsolete, the snippet
1134 should be copied to Documentation/snippets/new. The comments and
1135 texidoc strings should be removed as described above. Then the body
1136 of the snippet should be changed to:
1140 This snippet is deprecated as of version X.Y.Z and
1141 will be removed from the documentation.
1146 where X.Y.Z is the version number for which the convert-ly rule was
1149 Update the snippet files by running:
1152 scripts/auxiliar/makelsr.py
1155 Where the convert-ly rule is not able to automatically update regression
1156 tests, the regression tests in input/regression should be manually
1159 Although it is not required, it is helpful if the developer
1160 can write relevant material for inclusion in the Notation
1161 Reference. If the developer does not feel qualified to write
1162 the documentation, a documentation editor will be able to
1163 write it from the regression tests. The text that is added to
1164 or removed from the documentation should be changed only in
1165 the English version.
1167 @subsection Edit changes.tely
1169 An entry should be added to Documentation/changes.tely to describe
1170 the feature changes to be implemented. This is especially important
1171 for changes that change input file syntax.
1173 Hints for changes.tely entries are given at the top of the file.
1175 New entries in changes.tely go at the top of the file.
1177 The changes.tely entry should be written to show how the new change
1178 improves LilyPond, if possible.
1180 @subsection Verify successful build
1182 When the changes have been made, successful completion must be
1190 When these commands complete without error, the patch is
1191 considered to function successfully.
1193 Developers on Windows who are unable to build LilyPond should
1194 get help from a Linux or OSX developer to do the make tests.
1196 @subsection Verify regression test
1198 In order to avoid breaking LilyPond, it is important to verify that
1199 the regression tests all succeed. This process is described in
1200 @ref{Regression tests}.
1202 @subsection Post patch for comments
1204 For any change other than a minor change, a patch set should be
1205 posted on @uref{http://codereview.appspot.com/, Rietveld} for comment.
1206 This requires the use of an external package, git-cl, and an email
1209 git-cl is installed by:
1212 git clone git://neugierig.org/git-cl.git
1215 Then, add the git-cl directory to your PATH, or create a
1216 symbolic link to the git-cl and upload.py in one of your
1217 PATH directories (like usr/bin). git-cl is then
1218 configured by entering the command
1225 in the LilyPond git directory and answering the questions that
1226 are asked. If you do not understand the question answer with just
1229 The patch set is posted to Rietveld as follows. Ensure your changes
1230 are committed in a separate branch, which should differ from the
1231 reference branch to be used by just the changes to be uploaded.
1232 If the reference branch is to be origin/master, ensure this is
1233 up-to-date. If necessary, use git rebase to rebase the branch
1234 containing the changes to the head of origin/master. Finally,
1235 check out branch with the changes and enter the command:
1238 git cl upload <reference SHA1 ID>
1242 where <reference SHA1 ID> is the SHA1 ID of the commit to be used
1243 as a reference source for the patch. Generally, this will be the
1244 SHA1 ID of origin/master, and in that case the command
1247 git cl upload origin/master
1253 After prompting for your Google email address and password, the
1254 patch set will be posted to Rietveld.
1256 You should then announce the patch by sending
1257 an email to lilypond-devel, with a subject line
1258 starting with PATCH:, asking for comments on the patch.
1260 As revisions are made in response to comments, successive patch sets
1261 for the same issue can be uploaded by reissuing the git-cl command
1262 with the modified branch checked out.
1264 @subsection Push patch
1266 Once all the comments have been addressed, the patch can be pushed.
1268 If the author has push privileges, the author will push the patch.
1269 Otherwise, a developer with push privileges will push the patch.
1271 @subsection Closing the issues
1273 Once the patch has been pushed, all the relevant issues should be
1276 On Rietveld, the author should log in an close the issue either by
1277 using the @q{Edit Issue} link, or by clicking the circled x icon
1278 to the left of the issue name.
1280 If the changes were in response to a feature request on the Google
1281 issue tracker for LilyPond, the author should change the status to
1282 Fixed and a tag @q{fixed_x_y_z} should be added, where the patch was
1283 fixed in version x.y.z. If
1284 the author does not have privileges to change the status, an email
1285 should be sent to bug-lilypond requesting the BugMeister to change
1288 @node Iterator tutorial
1289 @section Iterator tutorial
1291 TODO -- this is a placeholder for a tutorial on iterators
1293 Iterators are routines written in C++ that process music expressions
1294 and sent the music events to the appropriate engravers and/or
1297 @node Engraver tutorial
1298 @section Engraver tutorial
1300 Engravers are C++ classes that catch music events and
1301 create the appropriate grobs for display on the page. Though the
1302 majority of engravers are responsible for the creation of a single grob,
1303 in some cases (e.g. @code{New_fingering_engraver}), several different grobs
1306 Engravers listen for events and acknowledge grobs. Events are passed to
1307 the engraver in time-step order during the iteration phase. Grobs are
1308 made available to the engraver when they are created by other engravers
1309 during the iteration phase.
1311 @subsection Useful methods for information processing
1313 An engraver inherits the following public methods from the Translator
1314 base class, which can be used to process listened events and acknowledged
1318 @item @code{virtual void initialize ()}
1319 @item @code{void start_translation_timestep ()}
1320 @item @code{void process_music ()}
1321 @item @code{void process_acknowledged ()}
1322 @item @code{void stop_translation_timestep ()}
1323 @item @code{virtual void finalize ()}
1326 These methods are listed in order of translation time, with
1327 @code{initialize ()} and @code{finalize ()} bookending the whole
1328 process. @code{initialize ()} can be used for one-time initialization
1329 of context properties before translation starts, whereas
1330 @code{finalize ()} is often used to tie up loose ends at the end of
1331 translation: for example, an unterminated spanner might be completed
1332 automatically or reported with a warning message.
1334 @subsection Translation process
1336 At each timestep in the music, translation proceeds by calling the
1337 following methods in turn:
1339 @code{start_translation_timestep ()} is called before any user
1340 information enters the translators, i.e., no property operations
1341 (\set, \override, etc.) or events have been processed yet.
1343 @code{process_music ()} and @code{process_acknowledged ()} are called
1344 after all events in the current time step have been heard, or all
1345 grobs in the current time step have been acknowledged. The latter
1346 tends to be used exclusively with engravers which only acknowledge
1347 grobs, whereas the former is the default method for main processing
1350 @code{stop_translation_timestep ()} is called after all user
1351 information has been processed prior to beginning the translation for
1354 @subsection Preventing garbage collection for SCM member variables
1356 In certain cases, an engraver might need to ensure private Scheme
1357 variables (with type SCM) do not get swept away by Guile's garbage
1358 collector: for example, a cache of the previous key signature which
1359 must persist between timesteps. The method
1360 @code{virtual derived_mark () const} can be used in such cases:
1363 Engraver_name::derived_mark ()
1365 scm_gc_mark (private_scm_member_)
1370 @subsection Listening to music events
1372 External interfaces to the engraver are implemented by protected
1373 macros including one or more of the following:
1376 @item @code{DECLARE_TRANSLATOR_LISTENER (event_name)}
1377 @item @code{IMPLEMENT_TRANSLATOR_LISTENER (Engraver_name, event_name)}
1381 where @var{event_name} is the type of event required to provide the
1382 input the engraver needs and @var{Engraver_name} is the name of the
1385 Following declaration of a listener, the method is implemented as follows:
1388 IMPLEMENT_TRANSLATOR_LISTENER (Engraver_name, event_name)
1390 Engraver_name::listen_event_name (Stream event *event)
1392 ...body of listener method...
1396 @subsection Acknowledging grobs
1398 Some engravers also need information from grobs as they are created
1399 and as they terminate. The mechanism and methods to obtain this
1400 information are set up by the macros:
1403 @item @code{DECLARE_ACKNOWLEDGER (grob_interface)}
1404 @item @code{DECLARE_END_ACKNOWLEDGER (grob_interface)}
1407 where @var{grob_interface} is an interface supported by the
1408 grob(s) which should be acknowledged. For example, the following
1409 code would declare acknowledgers for a @code{NoteHead} grob (via the
1410 @code{note-head-interface}) and any grobs which support the
1411 @code{side-position-interface}:
1414 @code{DECLARE_ACKNOWLEDGER (note_head)}
1415 @code{DECLARE_ACKNOWLEDGER (side_position)}
1418 The @code{DECLARE_END_ACKNOWLEDGER ()} macro sets up a spanner-specific
1419 acknowledger which will be called whenever a spanner ends.
1421 Following declaration of an acknowledger, the method is coded as follows:
1425 Engraver_name::acknowledge_interface_name (Grob_info info)
1427 ...body of acknowledger method...
1431 @subsection Engraver declaration/documentation
1433 An engraver must have a public macro
1436 @item @code{TRANSLATOR_DECLARATIONS (Engraver_name)}
1440 where @code{Engraver_name} is the name of the engraver. This
1441 defines the common variables and methods used by every engraver.
1443 At the end of the engraver file, one or both of the following
1444 macros are generally called to document the engraver in the
1445 Internals Reference:
1448 @item @code{ADD_ACKNOWLEDGER (Engraver_name, grob_interface)}
1449 @item @code{ADD_TRANSLATOR (Engraver_name, Engraver_doc,
1450 Engraver_creates, Engraver_reads, Engraver_writes)}
1454 where @code{Engraver_name} is the name of the engraver, @code{grob_interface}
1455 is the name of the interface that will be acknowledged,
1456 @code{Engraver_doc} is a docstring for the engraver,
1457 @code{Engraver_creates} is the set of grobs created by the engraver,
1458 @code{Engraver_reads} is the set of properties read by the engraver,
1459 and @code{Engraver_writes} is the set of properties written by
1462 @node Callback tutorial
1463 @section Callback tutorial
1465 TODO -- This is a placeholder for a tutorial on callback functions.
1467 @node LilyPond scoping
1468 @section LilyPond scoping
1470 The Lilypond language has a concept of scoping, ie you can do
1476 (display (+ foo 2)))
1479 @noindent with @code{\paper}, @code{\midi} and @code{\header} being
1480 nested scope inside the @file{.ly} file-level scope. @w{@code{foo = 1}}
1481 is translated in to a scheme variable definition.
1483 This implemented using modules, with each scope being an anonymous
1484 module that imports its enclosing scope's module.
1486 Lilypond's core, loaded from @file{.scm} files, is usually placed in the
1487 @code{lily} module, outside the @file{.ly} level. In the case of
1494 we want to reuse the built-in definitions, without changes effected in
1495 user-level @file{a.ly} leaking into the processing of @file{b.ly}.
1497 The user-accessible definition commands have to take care to avoid
1498 memory leaks that could occur when running multiple files. All
1499 information belonging to user-defined commands and markups is stored in
1500 a manner that allows it to be garbage-collected when the module is
1501 dispersed, either by being stored module-locally, or in weak hash
1504 @node LilyPond miscellany
1505 @section LilyPond miscellany
1507 This is a place to dump information that may be of use to developers
1508 but doesn't yet have a proper home. Ideally, the length of this section
1509 would become zero as items are moved to other homes.
1511 @subsection Spacing algorithms
1513 Here is information from an email exchange about spacing algorithms.
1515 On Thu, 2010-02-04 at 15:33 -0500, Boris Shingarov wrote:
1516 I am experimenting with some modifications to the line breaking code,
1517 and I am stuck trying to understand how some of it works. So far my
1518 understanding is that Simple_spacer operates on a vector of Grobs, and
1519 it is a well-known Constrained-QP problem (rods = constraints, springs
1520 = quadratic function to minimize). What I don't understand is, if the
1521 spacer operates at the level of Grobs, which are built at an earlier
1522 stage in the pipeline, how are the changes necessitated by differences
1523 in line breaking, taken into account? in other words, if I take the
1524 last measure of a line and place it on the next line, it is not just a
1525 matter of literally moving that graphic to where the start of the next
1526 line is, but I also need to draw a clef, key signature, and possibly
1527 other fundamental things -- but at that stage in the rendering
1528 pipeline, is it not too late??
1530 Joe Neeman answered:
1532 We create lots of extra grobs (eg. a BarNumber at every bar line) but
1533 most of them are not drawn. See the break-visibility property in
1536 @subsection Info from Han-Wen Email
1538 In 2004, Douglas Linhardt decided to try starting a document that would
1539 explain LilyPond architecture and design principles. The material below
1540 is extracted from that email, which can be found at
1541 @uref{http://thread.gmane.org/gmane.comp.gnu.lilypond.devel/2992}.
1542 The headings reflect questions from Doug or comments from Han-Wen;
1543 the body text are Han-Wen's answers.
1545 @unnumberedsubsubsec Figuring out how things work.
1547 I must admit that when I want to know how a program works, I use grep
1548 and emacs and dive into the source code. The comments and the code
1549 itself are usually more revealing than technical documents.
1551 @unnumberedsubsubsec What's a grob, and how is one used?
1553 Graphical object - they are created from within engravers, either as
1554 Spanners (derived class) -slurs, beams- or Items (also a derived
1555 class) -notes, clefs, etc.
1557 There are two other derived classes System (derived from Spanner,
1558 contaning a "line of music") and Paper_column (derived from Item, it
1559 contains all items that happen at the same moment). They are separate
1560 classes because they play a special role in the linebreaking process.
1562 @unnumberedsubsubsec What's a smob, and how is one used?
1564 A C(++) object that is encapsulated so it can be used as a Scheme
1565 object. See GUILE info, "19.3 Defining New Types (Smobs)"
1567 @unnumberedsubsubsec When is each C++ class constructed and used
1574 In the parser.yy see the macro calls MAKE_MUSIC_BY_NAME().
1579 Constructed during "interpreting" phase.
1584 Executive branch of Contexts, plugins that create grobs, usually one
1585 engraver per grob type. Created together with context.
1595 These are not C++ classes per se. The idea of a Grob interface hasn't
1596 crystallized well. ATM, an interface is a symbol, with a bunch of grob
1597 properties. They are not objects that are created or destroyed.
1602 Objects that walk through different music classes, and deliver events
1603 in a synchronized way, so that notes that play together are processed
1604 at the same moment and (as a result) end up on the same horizontal position.
1606 Created during interpreting phase.
1608 BTW, the entry point for interpreting is ly:run-translator
1609 (ly_run_translator on the C++ side)
1613 @unnumberedsubsubsec Can you get to Context properties from a Music object?
1615 You can create music object with a Scheme function that reads context
1616 properties (the \applycontext syntax). However, that function is
1617 executed during Interpreting, so you can not really get Context
1618 properties from Music objects, since music objects are not directly
1619 connected to Contexts. That connection is made by the Music_iterators
1621 @unnumberedsubsubsec Can you get to Music properties from a Context object?
1623 Yes, if you are given the music object within a Context
1624 object. Normally, the music objects enter Contexts in synchronized
1625 fashion, and the synchronization is done by Music_iterators.
1627 @unnumberedsubsubsec What is the relationship between C++ classes and Scheme objects?
1629 Smobs are C++ objects in Scheme. Scheme objects (lists, functions) are
1630 manipulated from C++ as well using the GUILE C function interface
1633 @unnumberedsubsubsec How do Scheme procedures get called from C++ functions?
1635 scm_call_*, where * is an integer from 0 to 4.
1636 Also scm_c_eval_string (), scm_eval ()
1638 @unnumberedsubsubsec How do C++ functions get called from Scheme procedures?
1640 Export a C++ function to Scheme with LY_DEFINE.
1642 @unnumberedsubsubsec What is the flow of control in the program?
1644 Good question. Things used to be clear-cut, but we have Scheme
1645 and SMOBs now, which means that interactions do not follow a very
1646 rigid format anymore. See below for an overview, though.
1648 @unnumberedsubsubsec Does the parser make Scheme procedure calls or C++ function calls?
1650 Both. And the Scheme calls can call C++ and vice versa. It's nested,
1651 with the SCM datatype as lubrication between the interactions
1653 (I think the word "lubrication" describes the process better than the
1654 traditional word "glue")
1656 @unnumberedsubsubsec How do the front-end and back-end get started?
1658 Front-end: a file is parsed, the rest follows from that. Specifically,
1660 Parsing leads to a Music + Music_output_def object (see parser.yy,
1661 definition of toplevel_expression )
1663 A Music + Music_output_def object leads to a Global_context object (see
1664 ly_run_translator ())
1666 During interpreting, Global_context + Music leads to a bunch of
1667 Contexts. (see Global_translator::run_iterator_on_me () )
1669 After interpreting, Global_context contains a Score_context (which
1670 contains staves, lyrics etc.) as a child. Score_context::get_output ()
1671 spews a Music_output object (either a Paper_score object for notation
1672 or Performance object for MIDI).
1674 The Music_output object is the entry point for the backend. (see
1675 ly_render_output () )
1677 The main steps of the backend itself are in
1682 paper-score.cc , Paper_score::process_
1685 system.cc , System::get_lines()
1688 The step, where things go from grobs to output, is in
1689 System::get_line(): each grob delivers a Stencil (a Device
1690 independent output description), which is interpreted by our
1691 outputting backends (scm/output-tex.scm and scm/output-ps.scm)
1692 to produce TeX and PS.
1696 Interactions between grobs and putting things into .tex and .ps files
1697 have gotten a little more complex lately. Jan has implemented
1698 page-breaking, so now the backend also involves Paper_book,
1699 Paper_lines and other things. This area is still heavily in flux, and
1700 perhaps not something you should want to look at.
1702 @unnumberedsubsubsec How do the front-end and back-end communicate?
1704 There is no communication from backend to front-end. From front-end to
1705 backend is simply the program flow: music + definitions gives
1706 contexts, contexts yield output, after processing, output is written
1709 @unnumberedsubsubsec Where is the functionality associated with KEYWORDs?
1711 See my-lily-lexer.cc (keywords, there aren't that many) and ly/*.ly
1712 (most of the other backslashed \words are identifiers)
1714 @unnumberedsubsubsec What Contexts/Properties/Music/etc. are available when they are processed?
1716 What do you mean exactly with this question?
1718 See ly/engraver-init.ly for contexts, see scm/define-*.scm for other
1721 @unnumberedsubsubsec How do you decide if something is a Music, Context, or Grob property?
1722 Why is part-combine-status a Music property when it seems (IMO)
1723 to be related to the Staff context?
1725 The Music_iterators and Context communicate through two channels
1727 Music_iterators can set and read context properties, idem for
1728 Engravers and Contexts
1730 Music_iterators can send "synthetic" music events (which aren't in
1731 the input) to a context. These are caught by Engravers. This is
1732 mostly a one way communication channel.
1734 part-combine-status is part of such a synthetic event, used by
1735 Part_combine_iterator to communicate with Part_combine_engraver.
1738 @unnumberedsubsubsec I'm adding a property to affect how \autochange works. It seems to
1739 me that it should be a context property, but the Scheme autochange
1740 procecure has a Music argument. Does this mean I should use
1743 \autochange is one of these extra strange beasts: it requires
1744 look-ahead to decide when to change staves. This is achieved by
1745 running the interpreting step twice (see scm/part-combiner.scm , at
1746 the bottom), and storing the result of the first step (where to switch
1747 staves) in a Music property. Since you want to influence that
1748 where-to-switch list, your must affect the code in
1749 make-autochange-music (scm/part-combiner.scm). That code is called
1750 directly from the parser and there are no official "parsing
1751 properties" yet, so there is no generic way to tune \autochange. We
1752 would have to invent something new for this, or add a separate
1756 \autochange #around-central-C ..music..
1760 where around-central-C is some function that is called from
1761 make-autochange-music.
1763 @unnumberedsubsubsec I get lost figuring out what environment the code I'm looking at is in when it executes.
1764 I found both the C++ and Scheme autochange code. Then I was
1765 trying to figure out where the code got called from. I finally figured out that
1766 the Scheme procedure was called before the C++ iterator code, but it took me a
1767 while to figure that out, and I still didn't know who did the calling in the
1768 first place. I only know a little bit about Flex and Bison, so reading those
1769 files helped only a little bit.
1771 @emph{Han-Wen:} GDB can be of help here. Set a breakpoint in C++, and run. When you
1772 hit the breakpoint, do a backtrace. You can inspect Scheme objects
1773 along the way by doing
1776 p ly_display_scm(obj)
1779 this will display OBJ through GUILE.
1781 @subsection Music functions and GUILE debugging
1783 Ian Hulin was trying to do some debugging in music functions, and
1784 came up with the following question
1787 I'm working on the Guile Debugger Stuff, and would like to try
1788 debugging a music function definition such as:
1791 conditionalMark = #(define-music-function (parser location) ()
1792 #@{ \tag #'instrumental-part @{\mark \default@} #@} )
1795 It appears conditionalMark does not get set up as an
1796 equivalent of a Scheme
1799 (define conditionalMark = define-music-function(parser location () ...
1803 although something gets defined because Scheme apparently recognizes
1806 #(set-break! conditionalMark)
1810 later on in the file without signalling any Guile errors.
1812 However the breakpoint trap is never encountered as
1813 define-music-function passed things on to ly:make-music-function,
1814 which is really C++ code ly_make_music_function, so Guile never
1815 finds out about the breakpoint.
1817 Han-Wen answered as follows:
1819 You can see the defintion by doing
1822 #(display conditionalMark)
1826 inside the .ly file.
1828 The breakpoint failing may have to do with the call sequence. See
1829 parser.yy, run_music_function(). The function is called directly from
1830 C++, without going through the GUILE evaluator, so I think that is why
1831 there is no debugger trap.