@c -*- coding: utf-8; mode: texinfo; -*-
@node Working on LilyPond projects
@chapter Working on LilyPond projects

This section explains a how to solve or avoid certain common
problems.  If you have programming experience, many of these
tips may seem obvious; you may wish to simply skim this
chapter.


@menu
* Suggestions for writing LilyPond files::  
* Updating old files::          
* Troubleshooting (taking it all apart)::  
* Saving typing with identifiers::  
* Style sheets::                
@end menu


@node Suggestions for writing LilyPond files
@section Suggestions for writing LilyPond files

Now you're ready to begin writing larger LilyPond files -- not just the
little examples in the tutorial, but whole pieces.  But how should you
go about doing it?

The best answer is ``however you want to do it.''  As long as LilyPond
can understand your files and produces the output that you want, it
doesn't matter what your files look like.  That said, sometimes we
make mistakes when writing files.  If LilyPond can't understand your
files, or produces output that you don't like, how do you fix the
problem?

Here are a few suggestions that can help you to avoid or fix
problems:

@itemize @bullet
@item @strong{Include @code{\version} numbers in every file}.  Note that all
templates contain a @code{\version "2.8.0"} string.  We
highly recommend that you always include the @code{\version}, no matter
how small your file is.  Speaking from personal experience, it's
quite frustrating to try to remember which version of LilyPond you were
using a few years ago.  @code{convert-ly} requires you to declare
which version of LilyPond you used.

@item @strong{Include checks}: @ref{Bar check}s and @ref{Octave check}s.  If you
include checks every so often, then if you make a mistake, you can pinpoint
it quicker.  How often is ``every so often''?  It depends on the complexity
of the music.  For very simple music, perhaps just once or twice.  For
very complex music, perhaps every bar.

@item @strong{One bar per line of text}.  If there is anything complicated, either in the music
itself or in the output you desire, it's often good to write only one bar
per line.  Saving screen space by cramming eight bars per line just isn't
worth it if you have to `debug' your files.

@item @strong{Comment your files}, with either bar numbers (every so often) or
references to musical themes (``second theme in violins'', ``fourth
variation'').  You may not need it when you're writing the piece for
the first time, but if you want to go back and change something two
or three years later, you won't know how your file is structured if you
didn't comment the file.

@item @strong{Indent your braces}.  A lot of problems are caused by an imbalance
in the number of @code{@{} and @code{@}}.

@end itemize




If you are entering music from an existing score (i.e. typesetting a
piece of existing sheet music),

@itemize @bullet

@item Enter one manuscript (the physical copy) system at a time (but still
only one bar per line of text), and
check each system when you finish it.  You may use the
@code{showLastLength} command to speed up processing -- see
@ref{Skipping corrected music}.

@item Define @code{mBreak = @{ \break @}} and insert @code{\mBreak}
in the input file whenever the manuscript has a line break.  This
makes it much easier to compare the LilyPond music to the original
music.  When you are finished proofreading your score, you may
define @code{mBreak = @{ @}} to remove all those line breaks.  This
will allow LilyPond to place line breaks wherever it feels are
best.

@end itemize


@node Updating old files
@section Updating old files

The LilyPond input syntax occasionally changes.  As LilyPond itself
improves, the syntax (input language) is modified accordingly.  Sometimes
the changes are made to make the input easier to read and write, and
sometimes the changes are made to accomodate new features of LilyPond.

LilyPond comes with a file that makes this updating easier:
@code{convert-ly}.  For details about how to run this program, see
@ref{Updating files with convert-ly}.

Unforunately, @code{convert-ly} cannot handle all input changes.  It
takes care of simple search-and-replace changes (such as @code{raggedright}
becoming @code{ragged-right}), but some changes are too
complicated.  The syntax changes that @code{convert-ly} cannot handle
are listed in @ref{Updating files with convert-ly}.

For example, in LilyPond 2.4 and earlier, accents and non-English
letters were entered using LaTeX -- for example,
"@code{No\"el}" (Christmas).  In LilyPond 2.6 and above, the special
"@code{ë}" must be entered directly into the LilyPond file as an
UTF-8 character.  @code{convert-ly} cannot change all the LaTeX
special characters into UTF-8 characters; you must manually update
your old LilyPond files.


@node Troubleshooting (taking it all apart)
@section Troubleshooting (taking it all apart)

Sooner or later, you will write a file that LilyPond cannot
compile.  The messages that LilyPond gives may help
you find the error, but in many cases you need to do some
investigation to determine the source of the problem.

The most powerful tools for this purpose are the
single line comment (indicated by @code{%}) and the block
comment (indicated by @code{%@{ ... %@}}).  If you don't
know where a problem is, start commenting out huge portions
of your input file.  After you comment out a section, try
compiling the file again.  If it works, then the problem
must exist in the portion you just commented.  If it doesn't
work, then keep on commenting out material until you have
something that works.

In an extreme case, you might end up with only

@example
\score @{
  <<
    % \melody
    % \harmony
    % \bass
  >>
  \layout@{@}
@}
@end example

@noindent
(in other words, a file without any music)

If that happens, don't give up.  Uncomment a bit -- say,
the bass part -- and see if it works.  If it doesn't work,
then comment out all of the bass music (but leave
@code{\bass} in the @code{\score} uncommented.

@example
bass = \relative c' @{
%@{
  c4 c c c
  d d d d
%@}
@}
@end example

Now start slowly uncommenting more and more of the
@code{bass} part until you find the problem line.


@node Saving typing with identifiers
@section Saving typing with identifiers

By this point, you've seen this kind of thing:

@lilypond[quote,verbatim,ragged-right]
hornNotes = \relative c'' { c4 b dis c }
\score {
  {
    \hornNotes
  }
}
@end lilypond

You may even realize that this could be useful in minimalist music:

@lilypond[quote,verbatim,ragged-right]
fragA = \relative c'' { a4 a8. b16 }
fragB = \relative c'' { a8. gis16 ees4 }
violin = \new Staff { \fragA \fragA \fragB \fragA }
\score {
  {
    \violin
  }
}
@end lilypond

However, you can also use these identifiers (also known as
variables, macros, or (user-defined) command) for tweaks:

@lilypond[quote,verbatim,ragged-right]
dolce = \markup{ \italic \bold dolce }
padText = { \once \override TextScript #'padding = #5.0 }
fthenp=_\markup{ \dynamic f \italic \small { 2nd } \hspace #0.1 \dynamic p }
violin = \relative c'' {
  \repeat volta 2 {
    c4._\dolce b8 a8 g a b |
    \padText
    c4.^"hi there!" d8 e' f g d |
    c,4.\fthenp b8 c4 c-. |
  }
}
\score {
  {
    \violin
  }
\layout{ragged-right=##t}
}
@end lilypond

These identifiers are obviously useful for saving
typing.  But they're worth considering even if you
only use them once -- they reduce complexity.  Let's
look at the previous example without any
identifiers.  It's a lot harder to read, especially
the last line.

@example
violin = \relative c'' @{
  \repeat volta 2 @{
    c4._\markup@{ \italic \bold dolce @} b8 a8 g a b |
    \once \override TextScript #'padding = #5.0 
    c4.^"hi there!" d8 e' f g d |
    c,4.\markup@{ \dynamic f \italic \small @{ 2nd @}
      \hspace #0.1 \dynamic p @} b8 c4 c-. |
  @}
@}
@end example

So far we've seen static substitution -- when LilyPond
sees @code{\padText}, it replaces it with the stuff that
we've defined it to be (ie the stuff to the right of
@code{padtext=}).

LilyPond can handle non-static substitution, too (you
can think of these as functions).

@lilypond[quote,verbatim,ragged-right]
padText =
#(define-music-function (parser location padding) (number?)
 #{
    \once \override TextScript #'padding = #$padding
 #})

\relative c''' {
  c4^"piu mosso" b a b
  \padText #1.8
  c4^"piu mosso" d e f
  \padText #2.6
  c4^"piu mosso" fis a g
}
@end lilypond

Using identifiers is also a good way to reduce work if the
LilyPond input syntax changes (see @ref{Updating old files}).  If
you have a single definition (such as @code{\dolce}) for all your
files (see @ref{Style sheets}), then if the syntax changes, you
only need to update your single @code{\dolce} definition,
instead of making changes throughout every @code{.ly} file.


@node Style sheets
@section Style sheets

The output that LilyPond produces can be heavily modified; see
@ref{Tweaking output} for details.  But what if you have many
files that you want to apply your tweaks to?  Or what if you
simply want to separate your tweaks from the actual music?  This
is quite easy to do.

Let's look at an example.  Don't worry if you don't understand
the parts with all the #().  This is explained in
@ref{Advanced tweaks with scheme}.

@lilypond[quote,verbatim,ragged-right]
mpdolce = #(make-dynamic-script (markup #:hspace 1 #:translate (cons 5 0)
  #:line(#:dynamic "mp" #:text #:italic "dolce" )))
tempoMark = #(define-music-function (parser location markp) (string?)
#{
  \once \override Score . RehearsalMark #'self-alignment-X = #left
  \once \override Score . RehearsalMark #'no-spacing-rods = ##t
  \mark \markup { \bold $markp }
#})

\relative c'' {
  \tempo 4=50
  a4.\mpdolce d8 cis4--\glissando a | b4 bes a2
  \tempoMark "Poco piu mosso"
  cis4.\< d8 e4 fis | g8(\! fis)-. e( d)-. cis2
}
@end lilypond

There are some problems with overlapping output; we'll fix those using
the techiques in @ref{Fixing overlapping notation}.  But let's also
do something about the @code{mpdolce} and @code{tempoMark}
definitions.  They produce the output we desire, but we might want
to use them in another piece.  We could simply copy-and-paste them
at the top of every file, but that's an annoyance.  It also leaves
those definitions in our music files, and I personally find all
the #() somewhat ugly.  Let's hide them in another file:

@example
%%% save this to a file called "definitions.ly"
mpdolce = #(make-dynamic-script (markup #:hspace 1 #:translate (cons 5 0)
  #:line(#:dynamic "mp" #:text #:italic "dolce" )))
tempoMark = #(define-music-function (parser location markp) (string?)
#@{
  \once \override Score . RehearsalMark #'self-alignment-X = #left
  \once \override Score . RehearsalMark #'no-spacing-rods = ##t
  \mark \markup @{ \bold $markp @}
#@})
@end example

Now let's modify our music (let's save this file as @file{"music.ly"}).

@c  We have to do this awkward example/lilypond-non-verbatim
@c  because we can't do the \include stuff in the manual.

@example
\include "definitions.ly"

\relative c'' @{
  \tempo 4=50
  a4.\mpdolce d8 cis4--\glissando a | b4 bes a2
  \once \override Score.RehearsalMark #'padding = #2.0
  \tempoMark "Poco piu mosso"
  cis4.\< d8 e4 fis | g8(\! fis)-. e( d)-. cis2
@}
@end example

@lilypond[quote,ragged-right]
mpdolce = #(make-dynamic-script (markup #:hspace 1 #:translate (cons 5 0)
  #:line(#:dynamic "mp" #:text #:italic "dolce" )))
tempoMark = #(define-music-function (parser location markp) (string?)
#{
  \once \override Score . RehearsalMark #'self-alignment-X = #left
  \once \override Score . RehearsalMark #'no-spacing-rods = ##t
  \mark \markup { \bold $markp }
#})

\relative c'' {
  \tempo 4=50
  a4.\mpdolce d8 cis4--\glissando a | b4 bes a2
  \once \override Score.RehearsalMark #'padding = #2.0
  \tempoMark "Poco piu mosso"
  cis4.\< d8 e4 fis | g8(\! fis)-. e( d)-. cis2
}
@end lilypond

That looks better, but let's make a few changes.  The glissando is hard
to see, so let's make it thicker and closer to the noteheads.  Let's
put the metronome marking above the clef, instead of over the first
note.  And finally, my composition professor hates "C" time signatures,
so we'd better make that "4/4" instead.

Don't change @file{music.ly}, though.  Replace our @file{definitions.ly}
with this:

@example
%%%  definitions.ly
mpdolce = #(make-dynamic-script (markup #:hspace 1 #:translate (cons 5 0)
  #:line( #:dynamic "mp" #:text #:italic "dolce" )))
tempoMark = #(define-music-function (parser location markp) (string?)
#@{
  \once \override Score . RehearsalMark #'self-alignment-X = #left
  \once \override Score . RehearsalMark #'no-spacing-rods = ##t
  \mark \markup @{ \bold $markp @}
#@})

\layout@{
  \context @{ \Score
    \override MetronomeMark #'extra-offset = #'(-9 . 0)
    \override MetronomeMark #'padding = #'3
  @}
  \context @{ \Staff
    \override TimeSignature #'style = #'numbered
  @}
  \context @{ \Voice
    \override Glissando #'thickness = #3
    \override Glissando #'gap = #0.1
  @}
@}
@end example

@lilypond[quote,ragged-right]
mpdolce = #(make-dynamic-script (markup #:hspace 1 #:translate (cons 5 0)
  #:line( #:dynamic "mp" #:text #:italic "dolce" )))
tempoMark = #(define-music-function (parser location markp) (string?)
#{
  \once \override Score . RehearsalMark #'self-alignment-X = #left
  \once \override Score . RehearsalMark #'no-spacing-rods = ##t
  \mark \markup { \bold $markp }
#})

\layout{
  \context { \Score
    \override MetronomeMark #'extra-offset = #'(-9 . 0)
    \override MetronomeMark #'padding = #'3
  }
  \context { \Staff
    \override TimeSignature #'style = #'numbered
  }
  \context { \Voice
    \override Glissando #'thickness = #3
    \override Glissando #'gap = #0.1
  }
}

\relative c'' {
  \tempo 4=50
  a4.\mpdolce d8 cis4--\glissando a | b4 bes a2
  \once \override Score.RehearsalMark #'padding = #2.0
  \tempoMark "Poco piu mosso"
  cis4.\< d8 e4 fis | g8(\! fis)-. e( d)-. cis2
} 
@end lilypond

That looks nicer!  But now suppose that I want to publish this
piece.  My composition professor doesn't like "C" time
signatures, but I'm somewhat fond of them.  Let's copy the
current @file{definitions.ly} to @file{web-publish.ly} and
modify that.  Since this music is aimed at produce a pdf which
will be displayed on the screen, we'll also increase the
overall size of the output.

@example
%%%  definitions.ly
mpdolce = #(make-dynamic-script (markup #:hspace 1 #:translate (cons 5 0)
  #:line( #:dynamic "mp" #:text #:italic "dolce" )))
tempoMark = #(define-music-function (parser location markp) (string?)
#@{
  \once \override Score . RehearsalMark #'self-alignment-X = #left
  \once \override Score . RehearsalMark #'no-spacing-rods = ##t
  \mark \markup @{ \bold $markp @}
#@})

#(set-global-staff-size 23)
\layout@{
  \context @{ \Score
    \override MetronomeMark #'extra-offset = #'(-9 . 0)
    \override MetronomeMark #'padding = #'3
  @}
  \context @{ \Staff
  @}
  \context @{ \Voice
    \override Glissando #'thickness = #3
    \override Glissando #'gap = #0.1
  @}
@}
@end example

@lilypond[quote,ragged-right]
mpdolce = #(make-dynamic-script (markup #:hspace 1 #:translate (cons 5 0)
  #:line( #:dynamic "mp" #:text #:italic "dolce" )))
tempoMark = #(define-music-function (parser location markp) (string?)
#{
  \once \override Score . RehearsalMark #'self-alignment-X = #left
  \once \override Score . RehearsalMark #'no-spacing-rods = ##t
  \mark \markup { \bold $markp }
#})

#(set-global-staff-size 23)
\layout{
  \context { \Score
    \override MetronomeMark #'extra-offset = #'(-9 . 0)
    \override MetronomeMark #'padding = #'3
  }
  \context { \Voice
    \override Glissando #'thickness = #3
    \override Glissando #'gap = #0.1
  }
}

\relative c'' {
  \tempo 4=50
  a4.\mpdolce d8 cis4--\glissando a | b4 bes a2
  \once \override Score.RehearsalMark #'padding = #2.0
  \tempoMark "Poco piu mosso"
  cis4.\< d8 e4 fis | g8(\! fis)-. e( d)-. cis2
} 
@end lilypond

Now in our music, I can either simply replace
@code{\include "definitions.ly"} with
@code{\include "web-publish.ly"}.  Of course, we could make this
even more convenient.  We could make a @file{definitions.ly} file which only
contains the definitions of @code{mpdolce} and @code{tempoMark}, a
@file{web-publish.ly} file which only contains the @code{\layout}
section listed above, and a @file{university.ly} file which
contains the tweaks to produce the output that my professor
prefers.  The top of @file{music.ly} would then look like this:

@example
\include "definitions.ly"

%%%  Only uncomment one of these two lines!
\include "web-publish.ly"
%\include "university.ly"
@end example

This approach can be useful even if you are only producing
one set of parts.  I use half a dozen different
"style sheet" files for my projects.  I begin every music
file with @code{\include "../global.ly"}, which contains

@example
%%%   global.ly
\version "2.8.0"
#(ly:set-option 'point-and-click #f)
\include "../init/init-defs.ly"
\include "../init/init-layout.ly"
\include "../init/init-headers.ly"
\include "../init/init-paper.ly"
@end example