lily-scheme function to display a chord both as music and as markup

Question

How to define a function that displays a chord both as music and as markup?

I'd like to get something like <c e g>1^\markup "c e g" without doubling the chord (c e g). E.g. with a function like \myFunction <c e g>

myFunction = #(define-music-function (myChord)
                (ly:music?)
                #{
                  $myChord^\markup {$myChord} % <- $myChord should be "expanded" as string in the markup
                #})

\relative c' {
  <c e g>1^\markup "c e g"
  \myFunction <c e g>
}

Answer 1

You need to extract the pitches and format them like this

myFunction =
#(define-music-function (myChord) (ly:music?)
   (let* ((elts (ly:music-property myChord 'elements))
          (pitches (map (lambda (x) (ly:music-property x 'pitch)) elts))
          (pitches (filter (lambda (x) (not (null? x))) pitches))
          (pitch-strings (map (lambda (x) (note-name->markup x #t)) pitches)))
     #{
       $myChord ^\markup $pitch-strings
     #}))

or maybe like this

#(define (format-pc pitch)
   (define (impl pitches)
     (if (null? pitches)
         (ly:error "Pitch name does not exist!")
         (let ((p (cdar pitches)))
           (if (and (= (ly:pitch-notename pitch) (ly:pitch-notename p))
                    (= (ly:pitch-alteration pitch) (ly:pitch-alteration p)))
               (caar pitches)
               (impl (cdr pitches))))))
   (symbol->string (impl pitchnames)))

myFunctionII =
#(define-music-function (myChord) (ly:music?)
   (let* ((elts (ly:music-property myChord 'elements))
          (pitches (map (lambda (x) (ly:music-property x 'pitch)) elts))
          (pitches (filter (lambda (x) (not (null? x))) pitches))
          (pitch-strings (map format-pc pitches)))
     #{
       $myChord ^\markup $pitch-strings
     #}))

Or maybe something like this if you want Lilypond code output

myFunctionIII =
#(define-music-function (myChord) (ly:music?)
   #{
     $myChord ^\markup #((@ (lily display-lily) music->lily-string) myChord)
   #})