Applying a rhythmic pattern (was Re: Macro with)

[Aaron Hill]

I was inspired by David's post, as I have also encountered patterns in 
durations that I wish were less redundant to input.  The snippet Malte 
linked to is rather complex, although I suspect it is significantly more 
air-tight at handling edge cases.

Here is a simpler (i.e. "one-pager") music function for applying a 
specified rhythmic pattern to some music:

%%%%
\version "2.19.83"

applyRhythm = #(define-music-function
  (rhythm notes) (ly:music? ly:music?)
  "Overwrites the durations of a simple music expression with
   those from another, repeating the rhythmic pattern as needed."
  (define (extract-durations music)
    (map (lambda (elem) (ly:music-property elem 'duration))
      (filter (music-type-predicate '(rhythmic-event))
        (ly:music-property music 'elements))))
  (define (apply-duration element duration)
    (let ((subelements (ly:music-property element 'elements)))
      (if (null? subelements)
        (set! (ly:music-property element 'duration) duration))
        (map (lambda (subelement)
            (set! (ly:music-property subelement 'duration) duration))
          subelements)))
  (define (apply-durations durations music)
    (for-each apply-duration
      (filter (music-type-predicate '(rhythmic-event event-chord))
        (ly:music-property music 'elements))
      (apply circular-list durations))
    music)
  #{ #(apply-durations (extract-durations rhythm) notes) #})

\fixed c' {
  \time 6/8
  \applyRhythm { 8. 16 8 } {
    | g\mp a <g b> a-\accent fis g~
    | <g b>\< c' <b d'>
  }
  <fis d'>4\mf r8
  \applyRhythm { 8. 16 8 4. } {
    | <e c'>( b <fis a> <d b^~>
    | <e b>) r <c fis>\f <b, g>\accent
  }
}
%%%%


-- Aaron Hill

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