Re: Part combiner warning about simultaneous breathing

[Devon Schudy]

David Kastrup wrote:
> My guess would be that the whole articulation mechanism might be
> changed in a manner that partcombine no longer is able to consider two
> articulations as mergeable.  In that case, it would likely be more than
> just breathings which are affected.

Yes: it's because that commit added the midi-length property to breath
marks (and some articulations), whose value is a function, so
partcombine can't tell they're identical.

The old definition of \breathe (without the offending property) gives
no warning:

breathe =
 #(define-music-function (parser location) ()
    (_i "Insert a breath mark.")
   (make-music 'BreathingEvent))

The simplest fix is to make \breathe use the same (eq?) closure
instead of a new one each time, so partcombine can merge the breaths:

#(define (breath-midi-length len context)
  ;;Shorten by half, or by up to a second, but always by a power of 2
  (let* ((desired (min (ly:moment-main (seconds->moment 1 context))
                       (* (ly:moment-main len) 1/2)))
         (scale (inexact->exact (ceiling (/ (log desired) (log 1/2)))))
         (breath (ly:make-moment (expt 1/2 scale))))
    (ly:moment-sub (ly:make-moment (ly:moment-main len)) breath)))

breathe =
#(define-music-function (parser location) ()
   (_i "Insert a breath mark.")
   (make-music 'BreathingEvent
     'midi-length breath-midi-length))

Articulations aren't affected, because they're just copied, not
created anew with a different midi-length function each time. User
code that creates custom articulations (or any music containing
closures) could have the same problem, though.