@chapter Programming work
@menu
-* Introduction to programming::
+* Overview of LilyPond architecture::
+* LilyPond programming languages::
* Programming without compiling::
* Finding functions::
* Code style::
* Debugging LilyPond::
-* other stuff::
@end menu
+@node Overview of LilyPond architecture
+@section Overview of LilyPond architecture
-@node Introduction to programming
-@section Introduction to programming
+LilyPond processes the input file into graphical and musical output in a
+number of stages. This process, along with the types of routines that
+accomplish the various stages of the process, is described in this section. A
+more complete description of the LilyPond architecture and internal program
+execution is found in Erik Sandberg's
+@uref{http://lilypond.org/web/images/thesis-erik-sandberg.pdf, master's
+thesis}.
-FIXME -- decide what goes in here and put it here. I'm not sure what
-should be here -- CDS
+
+The first stage of LilyPond processing is @emph{parsing}. In the parsing
+process, music expressions in LilyPond input format are converted to music
+expressions in Scheme format. In Scheme format, a music expression is a list
+in tree form, with nodes that indicate the relationships between various music
+events. The LilyPond parser is written in Bison.
+
+The second stage of LilyPond processing is @emph{iterating}. Iterating
+assigns each music event to a context, which is the environment in which the
+music will be finally engraved. The context is responsible for all further
+processing of the music. It is during the iteration stage that contexts are
+created as necessary to ensure that every note has a Voice type context (e.g.
+Voice, TabVoice, DrumVoice, CueVoice, MensuralVoice, VaticanaVoice,
+GregorianTranscriptionVoice), that the Voice type contexts exist in
+appropriate Staff type contexts, and that parallel Staff type contexts exist
+in StaffGroup type contexts. In addition, during the iteration stage each
+music event is assigned a moment, or a time in the music when the event
+begins.
+
+Each type of music event has an associated iterator. Iterators are defined in
+*-iterator.cc. During iteration, an
+event's iterator is called to deliver that music event to the appropriate
+context(s).
+
+The final stage of LilyPond processing is @emph{translation}. During
+translation, music events are prepared for graphical or midi output. The
+translation step is accomplished by translators or engravers (the distinction
+is unclear).
+
+Translators are defined in C++ files named *-engraver.cc. In *-engraver.cc, a
+C++ class of Engraver type is created. The Engraver is also declared as a
+translator. Much of the work of translating is handled by Scheme functions,
+which is one of the keys to LilyPond's exceptional flexibility.
+
+
+@node LilyPond programming languages
+@section LilyPond programming languages
+
+Programming in LilyPond is done in a variety of programming languages. Each
+language is used for a specific purpose or purposes. This section describes
+the languages used and provides links to reference manuals and tutorials for
+the relevant language.
+
+@subsection C++
+
+The core functionality of LilyPond is implemented in C++.
+
+C++ is so ubiquitous that it is difficult to identify either a reference
+manual or a tutorial. Programmers unfamiliar with C++ will need to spend some
+time to learn the language before attempting to modify the C++ code.
+
+The C++ code calls Scheme/GUILE through the GUILE interface, which is
+documented in the
+@uref{http://www.gnu.org/software/guile/manual/html_node/index.html, GUILE
+ Reference Manual}.
+
+@subsection GNU Bison
+
+The LilyPond parser is implemented in Bison, a GNU parser generator. The
+Bison homepage is found at @uref{http://www.gnu.org/software/bison/,
+gnu.org}. The manual (which includes both a reference and tutorial) is
+@uref{http://www.gnu.org/software/bison/manual/index.html, available} in a
+variety of formats.
+
+@subsection GNU Make
+
+GNU Make is used to control the compiling process and to build the
+documentation and the website. GNU Make documentation is available at
+@uref{http://www.gnu.org/software/make/manual/, the GNU website}.
+
+@subsection GUILE or Scheme
+
+GUILE is the dialect of Scheme that is used as LilyPond's extension language. Many extensions to LilyPond are written entirely in GUILE. The
+@uref{http://www.gnu.org/software/guile/manual/html_node/index.html,
+GUILE Reference Manual} is available online.
+
+@uref{http://mitpress.mit.edu/sicp/full-text/book/book.html, Structure and
+Interpretation of Computer Programs}, a popular textbook used to teach
+programming in Scheme is available in its entirety online.
+
+An introduction to Guile/Scheme as used in LilyPond can be found in the
+Learning Manual, see @rlearning{Scheme tutorial}.
+
+@subsection MetaFont
+
+MetaFont is used to create the music fonts used by LilyPond. A MetaFont
+tutorial is available at @uref{http://metafont.tutorial.free.fr/, the
+METAFONT tutorial page}.
+
+@subsection PostScript
+
+PostScript is used to generate graphical output. A brief PostScript tutorial
+is @uref{http://local.wasp.uwa.edu.au/~pbourke/dataformats/postscript/,
+available online}. The
+@uref{http://www.adobe.com/devnet/postscript/pdfs/PLRM.pdf, PostScript Lanugage
+Reference} is available online in PDF format.
+
+@subsection Python
+
+Python is used for XML2ly and is used for buillding the documentation and the
+website.
+
+Python documentation is available at @uref{http://www.python.org/doc/,
+python.org}.
@node Programming without compiling
@section Programming without compiling
For LilyPond files, you should follow the guidelines for LilyPond snippets
in the documentation. You can find these guidelines at
-@ref{Texinfo crash course}.
+@ref{Texinfo introduction and usage policy}.
@node Finding functions
@section Finding functions
Having identified a likely subdirectory to search, the grep utility can
be used to search for a function name. The format of the grep command is
-@example
+@example
grep -i functionName subdirectory/*
@end example
The most likely directories to grep for function names are scm/ for
scheme files, ly/ for lilypond input (*.ly) files, and lily/ for C++
-files.
+files.
@subsection Using git grep to search
@node Code style
-@section Code style
+@section Code style
@c email to wl@gnu.org when I get here.
@menu
Messages to be localised must be encapsulated in `_ (STRING)' or
`_f (FORMAT, ...)'. E.g.:
-@verbatim
- warning (_ ("need music in a score"));
- error (_f ("cannot open file: `%s'", file_name));
-@end verbatim
-
+@example
+warning (_ ("need music in a score"));
+error (_f ("cannot open file: `%s'", file_name));
+@end example
+
In some rare cases you may need to call `gettext ()' by hand. This
happens when you pre-define (a list of) string constants for later
use. In that case, you'll probably also need to mark these string
constants for translation, using `_i (STRING)'. The `_i' macro is
a no-op, it only serves as a marker for `xgettext'.
-@verbatim
-char const* messages[] = {
-_i ("enable debugging output"),
-_i ("ignore lilypond version"),
-0
-};
+@example
+char const* messages[] = @{
+ _i ("enable debugging output"),
+ _i ("ignore lilypond version"),
+ 0
+@};
void
foo (int i)
-{
-puts (gettext (messages i));
-}
-@end verbatim
-
+@{
+ puts (gettext (messages i));
+@}
+@end example
+
See also `flower/getopt-long.cc' and `lily/main.cc'.
@item
whitespace to be printed, prepend or append it to the translated
message
-@verbatim
+@example
message ("Calculating line breaks..." + " ");
-@end verbatim
+@end example
@item
Error or warning messages displayed with a file name and line
number never start with a capital, eg,
-@verbatim
+@example
foo.ly: 12: not a duration: 3
-@end verbatim
-
+@end example
+
Messages containing a final verb, or a gerund (`-ing'-form) always
start with a capital. Other (simpler) messages start with a
lowercase letter
-@verbatim
+@example
Processing foo.ly...
`foo': not declared.
Not declaring: `foo'.
-@end verbatim
-
+@end example
+
@item
Avoid abbreviations or short forms, use `cannot' and `do not'
rather than `can't' or `don't'
To avoid having a number of different messages for the same
-situation, we'll use quoting like this `"message: `%s'"' for all
+situation, well will use quoting like this `"message: `%s'"' for all
strings. Numbers are not quoted:
-@verbatim
+@example
_f ("cannot open file: `%s'", name_str)
_f ("cannot find character number: %d", i)
-@end verbatim
-
+@end example
+
@item
Think about translation issues. In a lot of cases, it is better to
-translate a whole message. The english grammar mustn't be imposed
+translate a whole message. The english grammar must not be imposed
on the translator. So, instead of
-@verbatim
+@example
stem at + moment.str () + does not fit in beam
-@end verbatim
-
+@end example
+
have
-@verbatim
+@example
_f ("stem at %s does not fit in beam", moment.str ())
-@end verbatim
-
+@end example
+
@item
Split up multi-sentence messages, whenever possible. Instead of
-@verbatim
+@example
warning (_f ("out of tune! Can't find: `%s'", "Key_engraver"));
warning (_f ("cannot find font `%s', loading default", font_name));
-@end verbatim
-
+@end example
+
rather say:
-@verbatim
-warning (out of tune:;
+@example
+warning (_ ("out of tune:"));
warning (_f ("cannot find: `%s', "Key_engraver"));
warning (_f ("cannot find font: `%s', font_name));
warning (_f ("Loading default font"));
-@end verbatim
-
+@end example
+
@item
If you must have multiple-sentence messages, use full punctuation.
Use two spaces after end of sentence punctuation. No punctuation
(esp. period) is used at the end of simple messages.
-@verbatim
- _f ("Non-matching braces in text `%s', adding braces", text)
- Debug output disabled. Compiled with NPRINT.
- _f ("Huh? Not a Request: `%s'. Ignoring.", request)
-@end verbatim
-
+@example
+_f ("Non-matching braces in text `%s', adding braces", text)
+_ ("Debug output disabled. Compiled with NPRINT.")
+_f ("Huh? Not a Request: `%s'. Ignoring.", request)
+@end example
+
@item
Do not modularise too much; words frequently cannot be translated
-without context. It's probably safe to treat most occurences of
+without context. It is probably safe to treat most occurences of
words like stem, beam, crescendo as separately translatable words.
@item
would mean sacrificing a bit of eloquency. This holds for original
messages too, of course.
-@verbatim
- en: cannot open: `foo.ly'
- + nl: kan `foo.ly' niet openen (1)
- kan niet openen: `foo.ly'* (2)
- niet te openen: `foo.ly'* (3)
-@end verbatim
+@example
+en: cannot open: `foo.ly'
++ nl: kan `foo.ly' niet openen (1)
+kan niet openen: `foo.ly'* (2)
+niet te openen: `foo.ly'* (3)
+@end example
+
-
The first nl message, although grammatically and stylistically
correct, is not friendly for parsing by humans (even if they speak
-dutch). I guess we'd prefer something like (2) or (3).
+dutch). I guess we would prefer something like (2) or (3).
@item
Do not run make po/po-update with GNU gettext < 0.10.35
Using a debugger simplifies troubleshooting in at least two ways.
First, breakpoints can be set to pause execution at any desired point.
-Then, when execution has paused, debugger commands can be issued to
+Then, when execution has paused, debugger commands can be issued to
explore the values of various variables or to execute functions.
Second, the debugger allows the display of a stack trace, which shows
@subsection Typical .gdbinit files
The behavior of gdb can be readily customized through the use of
-.gdbinit files. The file below is from Han-Wen. It sets breakpoints
+@var{.gdbinit} files. A @var{.gdbinit} file is a file named
+@var{.gdbinit} (notice the @qq{.} at the beginning of the file name)
+ that is placed in a user's home directory.
+
+The @var{.gdbinit} file below is from Han-Wen. It sets breakpoints
for all errors and defines functions for displaying scheme objects
(ps), grobs (pgrob), and parsed music expressions (pmusic).
@example
-file lily/out/lilypond
-b scm_error
-b programming_error
-b Grob::programming_error
-
-define ps
- print ly_display_scm($arg0)
- end
- define pgrob
- print ly_display_scm($arg0->self_scm_)
- print ly_display_scm($arg0->mutable_property_alist_)
- print ly_display_scm($arg0->immutable_property_alist_)
- print ly_display_scm($arg0->object_alist_)
- end
- define pmusic
- print ly_display_scm($arg0->self_scm_)
- print ly_display_scm($arg0->mutable_property_alist_)
- print ly_display_scm($arg0->immutable_property_alist_)
- end
+file lily/out/lilypond
+b scm_error
+b programming_error
+b Grob::programming_error
+
+define ps
+ print ly_display_scm($arg0)
+ end
+ define pgrob
+ print ly_display_scm($arg0->self_scm_)
+ print ly_display_scm($arg0->mutable_property_alist_)
+ print ly_display_scm($arg0->immutable_property_alist_)
+ print ly_display_scm($arg0->object_alist_)
+ end
+ define pmusic
+ print ly_display_scm($arg0->self_scm_)
+ print ly_display_scm($arg0->mutable_property_alist_)
+ print ly_display_scm($arg0->immutable_property_alist_)
+ end
@end example
+@subsection Using Guile interactively with LilyPond
+In order to experiment with Scheme programming in the LilyPond
+environment, it is convenient to have a Guile interpreter that
+has all the LilyPond modules loaded. This requires the following
+steps.
+First, define a Scheme symbol for the active module
+in the .ly file:
+@example
+#(module-define! (resolve-module '(guile-user))
+ 'lilypond-module (current-module))
+@end example
-@node other stuff
-@section other stuff
+Second, place a Scheme function in the .ly file that gives an interactive Guile
+prompt:
-Copied from an email from Carl. Maybe already included.
+@example
+#(top-repl)
+@end example
-- how to use a debugger with lilypond.
+When the .ly file is compiled, this causes the compilation to be interrupted
+and an interactive guile prompt to appear. When the guile prompt appears,
+the LilyPond active module must be set as the current guile module:
+
+@example
+guile> (set-current-module lilypond-module)
+@end example
+
+Proper operation of these commands can be demonstrated by typing the name
+of a LilyPond public scheme function to see if it's properly defined:
+
+@example
+guile> fret-diagram-verbose-markup
+#<procedure fret-diagram-verbose-markup (layout props marking-list)>
+@end example
+
+If the LilyPond module has not been correctly loaded, an error
+message will be generated:
+
+@example
+guile> fret-diagram-verbose-markup
+ERROR: Unbound variable: fret-diagram-verbose-markup
+ABORT: (unbound-variable)
+@end example
+
+Once the module is properly loaded, any valid LilyPond Scheme expression
+can be entered at the interactive prompt.
+
+After the investigation is complete, the interactive guile interpreter
+can be exited:
+
+@example
+guile> (quit)
+@end example
-- how to get lilypond running and pause at a guile prompt
+The compilation of the .ly file will then continue.
-- brief overview of how lilypond processes a file.
projects / lilypond.git / blobdiff