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Re: LSR 507 (ghost voice) broken since 2.15.28

From: David Kastrup
Subject: Re: LSR 507 (ghost voice) broken since 2.15.28
Date: Thu, 16 May 2013 15:06:37 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux)

David Kastrup <address@hidden> writes:

> David Kastrup <address@hidden> writes:
>> Eluze <address@hidden> writes:
>>> LSR 507 <http://lsr.dsi.unimi.it/LSR/Item?id=507> produces erroneous
>>> code since version 2.15.28:
>>> mus = { c4 d e f |}
>>> \displayLilyMusic \ghostMusic \mus
>> That's fallout from issue 2240, Patch: Don't wrap EventChord around
>> rhythmic events by default.  It won't be the only affected item.
>> The basic question is when should we be migrating the LSR to 2.16.
>> In this particular case, only the first of several "adjacent" spacers is
>> retained.  The reason for that apparently is to avoid <c e> getting
>> turned into what amounts to <s s>.  I don't think that this
>> simple-minded approach is all too likely to lead to sane results without
>> more effort, even pre-2.15.28.  So my take on this would be to just junk
>> the music-filter expression.  This is going to lead to constructs
>> occasionally that one can't actually enter, but which should at least
>> compile reasonably well.
> In a nutshell:
> ghostMusic =
> #(define-music-function (parser location music) (ly:music? )
>   (music-map (lambda (x)
>             (let ((dur (ly:music-property x 'duration)))
>              (if (ly:duration? dur)
>               (apply make-music 'SkipEvent
>                (flatten-alist
>                 (ly:music-mutable-properties x)))
>               x)))
>    music))
> notes = { a2-"hello" b4 r b2 a-"bye" <c e g c' e' g'>1-"oho ;-)" }
> \ghostMusic \notes
> This is not going to work out of the box with chord repetitions.

And here is a version that should work both with 2.14 as well as 2.16
and be fine with chord repetitions.

ghostMusic =
#(define-music-function (parser location music) (ly:music?)
    (lambda (x)
      (if (music-is-of-type? x 'rhythmic-event)
          (apply make-music 'SkipEvent
                  (ly:music-mutable-properties x)))

notes = { a2-"hello" b4 r b2 a-"bye" <c e g c' e' g'>1-"oho ;-)" }

\ghostMusic \notes

With 2.16 proper, one would likely rather use map-some-music and
(lambda (x) (and (music-is-of-type? ...) (apply ...)))

David Kastrup

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