\version "2.14.0"

\header {
  texidoc = "
 If you need to create scores for different audiences from the same
sources you need to filter the input. The \\tag command partially
addresses this, but source files have to be changed in order to create
different scores. This snippet shows how to use scheme code to filter
music expressions, markup expressions, set up header fields and layout
context overrides based on a switch passed on the command line.




The basic idea is to use a command line such as @code{lilypond
-dtarget=chords -o chords snippet.ly}, for example, to build a score
emphasizing chords. In the input file several facilities are provided:




* Music expressions are filtered using the construct @code{\\ifTargetIn
#'(<list of eligible targets>) expr}. If the target entered on the
command-line isn't in the list, then the expression won't be rendered.
* Markup expressions are filtered using the similar construct
@code{\\if-target-in #'(<list of eligible targets>) expr}. * The macro
@code{\\targetName} is provided and can be assigned to header fields.
This name isn't the actual text of the target but can be more exotic,
for example @code{'chords => \"Full accompaniment\"}. You just need to
set up the the target-names map correctly. * Context properties need to
be set in some cases, for instance in order reduce the size of a score
to get it on a single page. Luckily Lilypond allows this using a
construct like  @code{\\override LyricText #'font-size =
#(value-if-target-in '(chords) -1 0)}. 

"
  doctitle = "Filtering parts from the command line"
}
%%
%% Based on the ideas, work, hard slog and implementations of Nicolas Sceaux, 
%% (who also had to do the reviews.)
%%
%% current-target
%%	Target option passed on the command line. If none found, then use the
%%	target 'default
%%
#(define current-target (or (ly:get-option 'target) 'default))

%%
%% set-target!
%%	Utility routine to override the current target. Specifically used in 
%%	this snippet to simulate different passes over the input files.
%%	target	    symbol	New target (as if it had been set by -dtarget= 
%%
#(define (set-target! target)
	 (set! current-target target))

%% 
%% value-if-target-in
%%	Utility routine to set a value depending on whether the candidate 
%%	list contains the current-target.
%%	eligible    list	List of symbols
%%	value			Value to return if the eligible list contains 
%%				the current target.
%%	else-value		Value to return if the current target isn't in
%%				the list of eligible.
%%
#(define-macro (value-if-target-in eligible value else-value)
  `(if (memq current-target ,eligible)
       ,value
       ,else-value)) 

%%
%% target-names
%%	Map of target names
%%
#(define target-names 
	 '((chords ."With explicit chords") 
	   (song   ."With all lyrics")))

%%
%% Set up an instrument name for the header
%%
targetName = #(assoc-ref target-names current-target)

%%
%% ifTargetIn
%%	Render the music expression if the target is in the eligible list
%%
ifTargetIn =
#(define-music-function (parser location eligible music)
			(list? ly:music?)
  (value-if-target-in eligible music (make-music 'Music)))

%%
%% if-target-in
%%	Render the markup expression if the target is in the eligible list
%%
#(define-markup-command (if-target-in layout props eligible markp)
			(list? markup?)
  (value-if-target-in eligible
		      (interpret-markup layout props markp)
		      empty-stencil))

		      
%%% SNIPPET SPECIFIC WORKAROUND SECTION =================================
%%% THIS IS NOT PART OF THE EXAMPLE CODE -- JUST A WORKAROUND.
%%% As we fake the "-d target=xxx" command line switch by setting the 
%%% target option in the source file itself, and as when markup commands 
%%% are interpreted the whole file as been read long ago, the 
%%% \if-target-in markup command sees that the selected target option is 
%%% the last one set using set-target!
%%% In practice, the option would be set once, from the command line switch. 
%%% But here, as we fake in a single file the three possible calls, we use 
%%% this music function as a workaround.
toplevelMarkupIfTargets =
#(define-music-function (parser location eligible text)
                        (list? markup?)
   (if (memq current-target eligible)
       (collect-scores-for-book parser 
			        (if (>= (cadr (ly:version)) 11)
				    (list text)
				    text)))
       (make-music 'Music 'void #t))

%%% Redefine this as a no-op to still be able to use it in the examples
#(define-markup-command (if-target-in layout props eligible markp)
			(list? markup?)
    (interpret-markup layout props markp))

%%% END SNIPPET SPECIFIC WORKAROUND SECTION =============================

%% ======================================================================

txtChorus = \lyricmode {
  \set stanza = "Ch." This is a ve- ry me- lo- dious cho- rus.
}
txtVerseI = \lyricmode {
  \set stanza = "1." And this is the first verse of three. This
}
txtVerseII = \lyricmode {
  \set stanza = "2." And now this is the se- cond one.
}
txtVerseIII = \lyricmode {
  \set stanza = "3." And this is the end of my song.
}

mlChorus   = \markup { C. \italic { This is a very melodious chorus. } }
mlVerseI   = \markup { 1. And this is the first verse of three. }
mlVerseII  = \markup { 2. And now this is the second one. }
mlVerseIII = \markup { 3. And this is the end of my song.}

chdBoth = \chordmode { c4 g1 c g c }

treChorusI  = \relative c'' { g4 | a2 b4 c8 c16 d32 e | f2 e4 d | }
treVerseI  = \relative c'' { g4. a8 b4. c8 | g4 a8 b c b\rest g4 | }
treBothII = \relative c' { 
  s4 | e2 e2 | d8 e d e d e d e | d8 e d e d e d e | d8 e d e d s s4 | 
}
basBothI  = \relative c' { 
  c4 | b2 c2 | d2 c2 | b2 c2 | d2 c8 d,\rest c'4 | 
}
basBothII = \relative c { 
  c16 c c c | d16 e d e d e d e d e d e d e d e | 
  d16 e d e d e d e d e d e d e d e | 
  d16 e d e d e d e d e d e d e d e | 
  d16 e d e d e d e d e s8 c16 c c c | 
}

global = {
  \key c \major
  \time 4/4
  \partial 4 s4 s1*2 \bar "||"
  s1*2 \bar "|."
}



%% ======================================================================
%% FIRST PASS : Score with default target
%% Simulate the command > lilypond <filename>
\markup \box \line \typewriter { > lilypond <filename> }
targetName = #(assoc-ref target-names current-target)
%% ======================================================================
\score {
  \context ChoirStaff <<
    \ifTargetIn #'(orgue default) \new ChordNames { \chdBoth }
    \new Staff <<
      \global \clef treble
      {
	\new Voice = "chorus" {
	  \ifTargetIn #'(default) \voiceOne
	  \treChorusI
	}
	\break
	\new Voice = "verse" {
	  \ifTargetIn #'(default) \voiceOne
	  \treVerseI
	}
      }
      \\ \ifTargetIn #'(default) { \voiceTwo \treBothII }
    >>
    \lyricsto "chorus" \new Lyrics \txtChorus
    \lyricsto "verse" \new Lyrics \txtVerseI
    \ifTargetIn #'(song) <<
      \lyricsto "verse" \new Lyrics \txtVerseII
      \lyricsto "verse" \new Lyrics \txtVerseIII
    >>
    \ifTargetIn #'(default) \new Staff <<
      \global \clef bass
      \basBothI \\ \basBothII
    >>
    \ifTargetIn #'(chords) \new Staff <<
      \global \clef bass
      \transpose c c, \chdBoth
    >>
  >>
  \header { piece = \targetName }
  \layout { 
    \context { \Lyrics
      \override LyricText #'font-shape = #(value-if-target-in '(chords) 'italic 'upright)
    }
  }
}
\toplevelMarkupIfTargets #'(default)	% WORKAROUND - ignore this line
\markup \if-target-in #'(default) \fill-line {
  \column{
    \line{\pad-around #1.5 {\mlChorus}}
    \line{\pad-around #1.5 {\mlVerseI}}
    \line{\pad-around #1.5 {\mlVerseII}}
    \line{\pad-around #1.5 {\mlVerseIII}}
  }
}

%% ======================================================================
%% SECOND PASS : Score with `chords' target
%% Simulate the command > lilypond -dtarget=chords -o chords <filename>
#(set-target! 'chords)
\markup \box \line \typewriter { > lilypond -dtarget=chords -o chords <filename> }
targetName = #(assoc-ref target-names current-target)
%% ======================================================================

%\noPageBreak
\score {
  \context ChoirStaff <<
    \ifTargetIn #'(chords default) \new ChordNames { \chdBoth  }
    \new Staff <<
      \global \clef treble
      {
        \new Voice = "chorus" {
          \ifTargetIn #'(default) \voiceOne
          \treChorusI
        }
        \break
        \new Voice = "verse" {
          \ifTargetIn #'(default) \voiceOne
          \treVerseI
        }
      }
      \\ \ifTargetIn #'(default) { \voiceTwo \treBothII }
    >>
    \lyricsto "chorus" \new Lyrics \txtChorus
    \lyricsto "verse" \new Lyrics \txtVerseI
    \ifTargetIn #'(song) <<
      \lyricsto "verse" \new Lyrics \txtVerseII
      \lyricsto "verse" \new Lyrics \txtVerseIII
    >>
    \ifTargetIn #'(default) \new Staff <<
      \global \clef bass
      \basBothI \\ \basBothII 
    >>
    \ifTargetIn #'(chords) \new Staff <<
      \global \clef bass
      \transpose c c, \chdBoth
    >>
  >>
  \header { piece = \targetName }
  \layout { 
    \context { \Lyrics
      \override LyricText #'font-shape = #(value-if-target-in '(chords) 'italic 'upright)
    }
  }
}
\toplevelMarkupIfTargets #'(default) 	% WORKAROUND - ignore this line
\markup \if-target-in #'(default) \fill-line {
  \column{
    \line{\pad-around #1.5 {\mlChorus}}
    \line{\pad-around #1.5 {\mlVerseI}}
    \line{\pad-around #1.5 {\mlVerseII}}
    \line{\pad-around #1.5 {\mlVerseIII}}
  }
}

%% ======================================================================
%% THIRD PASS : Score with `song' target
%% Simulate the command > lilypond -dtarget=song -o song <filename>
#(set-target! 'song)
\markup \box \line \typewriter { > lilypond -dtarget=song -o song <filename> }
targetName = #(assoc-ref target-names current-target)
%% ======================================================================

%\noPageBreak
\score {
  \context ChoirStaff <<
    \ifTargetIn #'(chords default) \new ChordNames { \chdBoth }
    \new Staff <<
      \global \clef treble
      {
        \new Voice = "chorus" {
          \ifTargetIn #'(default) \voiceOne
          \treChorusI
        }
        \break
        \new Voice = "verse" {
          \ifTargetIn #'(default) \voiceOne
          \treVerseI
        }
      }
      \\ \ifTargetIn #'(default) { \voiceTwo \treBothII }
    >>
    \lyricsto "chorus" \new Lyrics \txtChorus
    \lyricsto "verse" \new Lyrics \txtVerseI
    \ifTargetIn #'(song) <<
      \lyricsto "verse" \new Lyrics \txtVerseII
      \lyricsto "verse" \new Lyrics \txtVerseIII
    >>
    \ifTargetIn #'(default) \new Staff <<
      \global \clef bass
      \basBothI \\ \basBothII 
    >>
    \ifTargetIn #'(chords) \new Staff <<
      \global \clef bass
      \transpose c c, \chdBoth
    >>
  >>
  \header { piece = \targetName }
  \layout { 
    \context { \Lyrics
      \override LyricText #'font-shape = #(value-if-target-in '(chords) 'italic 'upright)
    }
  }
}
\toplevelMarkupIfTargets #'(default) 	% WORKAROUND - ignore this line
\markup \if-target-in #'(default) \fill-line {
  \column{
    \line{\pad-around #1.5 {\mlChorus}}
    \line{\pad-around #1.5 {\mlVerseI}}
    \line{\pad-around #1.5 {\mlVerseII}}
    \line{\pad-around #1.5 {\mlVerseIII}}
  }
}