dynamically update lilypond variables (using scheme?)

Question

I have a bunch of organ scores with 4 voices (sopMusic, altoMusic, tenorMusic, bassMusic). Each of those voices consists of two alternating snippets of music. For example, under sopMusic we would find \sopranoOne and \sopranoTwo, both of which contain a couple measures of music. A simplified example would look like this:

sopMusic = {
    \global
    \voiceOne
    \sopranoOne 
    \sopranoTwo
    \sopranoOne 
    \sopranoTwo
}
altoMusic = {
    \global
    \voiceTwo
    \altoOne 
    \altoTwo
    \altoOne 
    \altoTwo
}
tenorMusic = {
    \global
    \voiceOne
    \tenorOne 
    \tenorTwo
    \tenorOne 
    \tenorTwo
}
bassMusic = {
    \global
    \voiceTwo
    \bassOne 
    \bassTwo
    \bassOne 
    \bassTwo
}

Typically I enter the correct number of repetitions in the soprano, and then copy/paste for the alto, tenor and bass parts. But this would be better done programmatically. Can somebody give me a function that will produce the altoMusic, tenorMusic, and bassMusic automatically given the sopMusic as an input?

Answer 1

Maybe something like this fits the bill?

%%% Predicate for number or #f
#(define (number-or-false? x) (or (number? x) (not x)))

%%% arrange music saved in alist @param part in order @param repetitions (a list of assoc keys). Optionally
%%% the voice number can be specified using @param voicenumber
unfoldRepetition =
#(define-music-function (repetitions voicenumber part) (list? (number-or-false? #f) list?)
   (make-music 'SequentialMusic
               'elements
               (if voicenumber
                   (cons (context-spec-music (make-voice-props-set (1- voicenumber))  'Voice)
                         (map (lambda (x) (ly:assoc-get x part)) repetitions))
                   (map (lambda (x) (ly:assoc-get x part)) repetitions))))

%%% DEFINING MUSIC
% This defines associated lists, which is nice to access from Scheme. We use 1,2 as keys, but this could be any symbol, e.g. one,two
soprano.1 = {
  c''4 d'' c'' d''
}

soprano.2 = {
  b'4 c'' b' c''
}

alto.1 = {
  g'2 f'
}

alto.2 = {
  e'2 d'
}

tenor.1 = {
  e'2 d'
}

tenor.2 = {
  a2 b
}

bass.1 = {
  c2 g
}

bass.2 = {
  a2 g
}
%%% DONE DEFINING MUSIC

%%% Define a list of repetitions
#(define repetitions '(1 2 1 2))

% Test for one voice without specifying voice number
\unfoldRepetition #repetitions #soprano

% Test for multiple voices with voice number (although not necessary)
\new ChoirStaff <<
  \new Staff << \unfoldRepetition #repetitions 1 #soprano \\ \unfoldRepetition #repetitions 2 #alto >>
  \new Staff { \clef bass << \unfoldRepetition #repetitions 1 #tenor \\ \unfoldRepetition #repetitions 2 #bass >> }
>>

%%% DEFINE A choir score FACTORY:
choirScore =
#(define-scheme-function (S A T B) (list? list? list? list?)
   (define-music-function (reps) (list?)
     #{
       \new ChoirStaff <<
         \new Staff << \unfoldRepetition #reps 1 #S \\ \unfoldRepetition #reps 2 #A >>
         \new Staff { \clef bass << \unfoldRepetition #reps 1 #T \\ \unfoldRepetition #reps 2 #B >> }
       >>
     #}))

%% Test
myChoirFactory = \choirScore #soprano #alto #tenor #bass

\myChoirFactory #repetitions
\myChoirFactory #'(1 2 1)