Learning LilyPond - Parser permissiveness

[Colin Tennyson]

I noticed that in some places there is remarkable freedom to exchange order
and grouping of commands.

Take the following nesting structure:

addKey = { \key c \major  \time 4/4 }
instrOne = { \set Staff.instrumentName = #"Superius " }
instrTwo = { \set Staff.instrumentName = #"Contratenor " }

\score {
  \new StaffGroup
  <<
    \new Staff 
    <<
      \new Voice = "staffOne" { \instrOne \addKey \staffOneNotes }
      \new Lyrics \lyricsto "staffOne" \staffOneWords
      \barSetup
    >>
    \new Staff 
    <<
      \instrTwo \addKey \new Voice = "staffTwo" \staffTwoNotes 
      \lyricsto "staffTwo" \new Lyrics \staffTwoWords
      \barSetup
    >>
  >>
}


\new Voice = "staffOne" { \instrOne \addKey \staffOneNotes }
\new Lyrics \lyricsto "staffOne" \staffOneWords

versus:

\instrTwo \addKey \new Voice = "staffTwo" \staffTwoNotes
\lyricsto "staffTwo" \new Lyrics \staffTwoWords 


Both are accepted by the parser, and they are rendered identically.

I'm amazed that the parser is able to disambiguate the source code. There
are no delimiters between the expressions. How does the parser figure out
where one expression has ended, and the next one has begun?

If I hazard a guess it seems likely that it's best to put the keyword \new
at the start of the expression. It looks really odd to first specify
\lyricsto, and after that instantiate a new Lyrics context. Still, it
renders correctly.

The graphical output is rendered identially, but maybe it makes a different
for the MIDI output, such as creating a spurious empty track that shows up
when you later open the MIDI file with a MIDI editor. 



++++++++++++++++++++++++++++++++++++++++++++++++++

\version "2.18.0"
\language "english"

% 't' as in 'test' or 'transcribing an existing score'
tBreak = { \break }
ficta = { \once \set suggestAccidentals = ##t }

barSetup = {
  % for the Mensurstriche: inside the staff hide the barline
  \override Staff.BarLine.transparent = ##t
  % for the Mensurstriche: inside the staff hide the barline
  %\override Staff.BarLine.stencil = ##f  
  s1 |         s1 |         s1 | \tBreak s1 |         s1 |         %05
  s1 |         s1 |         s1 | \tBreak s1 |         s1 |         %10
  \override Staff.BarLine.transparent = ##f \bar "||" % final barline
visible
  %\override Staff.BarLine.stencil = ##t  
}
staffOneNotes =  \relative c'' {
  g1 | g2 a2 | b2 g2 | r2 a2 | d2. c4 | %005
  b2 a2 | r4 d4 d4 b4 | c4. b8 a8[ g8] a4. g8[ f8 e8] d4 a'2  g2 \ficta fs4
|  %010
}
staffOneWords = \lyricmode { 
  San -- | cta Ma -- | ri -- a,  San -- | cta Ma -- | %005
  ri -- a,   suc -- cur -- re |  mi- _ _ _ _    _ _ _ _ _   _ %010
}
staffTwoNotes =  \relative c' { 
  %\clef "G_8"
  g2 c2.  d4 a2 | g4. a8 b8[ c8] d2 cs4 d2 | r4  d2 d4 |  %005
  e2 f2 | d2 r2 | c2 f2. d4 f2 | e2 d4. c8 | %010
}
staffTwoWords = \lyricmode { 
  San -- cta Ma -- ri -- _ _ _ _ _   _ a, San -- cta %05
  Ma -- ri -- a, suc -- cur -- re mi -- se- _ _  %10
}

\header {
  title = "Sancta Maria, succurre miseris"
  composer = "Philippe Verdelot"
  tagline = ""
}

addKey = { \key c \major  \time 4/4 }
instrOne = { \set Staff.instrumentName = #"Superius " }
instrTwo = { \set Staff.instrumentName = #"Contratenor " }

\score {
  \new StaffGroup
  <<
    \new Staff 
    <<
      \new Voice = "staffOne" { \instrOne \addKey \staffOneNotes }
      \new Lyrics \lyricsto "staffOne" \staffOneWords
      \barSetup
    >>
    \new Staff 
    <<
      \instrTwo \addKey \new Voice = "staffTwo" \staffTwoNotes 
      \lyricsto "staffTwo" \new Lyrics \staffTwoWords
      \barSetup
    >>
  >>

  \layout 
  { 
    indent = 50
    \override Score.SystemStartBracket.transparent = ##t
    \override Score.BarNumber.font-size = #1
    \override Score.BarNumber.break-visibility = #end-of-line-invisible 
    \override Score.BarNumber.self-alignment-X = #LEFT 
    \set Score.barNumberVisibility = #(every-nth-bar-number-visible 5) 
    \override Staff.InstrumentName.self-alignment-X = #RIGHT    
    \context { \Voice \remove "Forbid_line_break_engraver" }
    ragged-last = ##t
    #(layout-set-staff-size 18)
  }
  %\midi { }
}

\paper {
  left-margin = 30
  right-margin = 30
}



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