Passing chords to and returning music with Lilypond music substitution functions

Question

I am trying to write functions in Lilypond which take a chord (or list of pitches) as an argument and return music with said chord inserted into a rhythm. More specifically, I would like the function to be invoked in some way like this:

\chordFunction <c ef f af>
% or
\chordFunction #'(c ef f af)

and to return Lilypond code like so:

\tuplet 3/2 {<c ef f af>4 <c ef f af>8~} <c ef f af>2

I have tried

jazzsyncoA = 
#(define-music-function
  (parser location chord)
  (symbol-list-or-music?)
  #{
    \tuplet 3/2 {$<chord>4 $<chord>8~} $<chord>2
  #}
)

but that throws

error: GUILE signaled an error for the expression beginning here
    \tuplet 3/2 {$
                  <chord>4 $<chord>8~} $<chord>2

along with other errors when I attempt invocation. How should I write functions to accomplish this? Am I approaching the problem improperly?

I've looked in the Lilypond docs on predefined type predicates, but I can't recognize any of potential use.

score 1 · Accepted Answer · answered Jan 20 '19 at 08:01

I think you're more or less in the right direction. You could look at this LilyPond doc page to see how you might get started writing a pure Scheme function to solve this and other problems.

As for your function, if you want to use your function like \chordFunction <c ef f af>, then you could ly:music? as the predicate:

\version "2.18.0"
\language "english"

jazzsyncoA = #(define-music-function (parser location my-notes) (ly:music?)
    #{
        \tuplet 3/2 {  #my-notes q8~ } q2
    #}
)

\score {
    \new Staff {
        \clef "bass"
        \key c \minor
        \new Voice = "one" {
            \jazzsyncoA <c ef f af>4
        }
    }
}

This gives the the same result as what's in your picture. I tested this on version 2.19.82, but I'm guessing that it will work on 2.18.0 as well. Hope that it helps!

Passing chords to and returning music with Lilypond music substitution functions

1 Answers1