Re: How to define functions that generate music functions?

[Juha Erkkila]

On Wed, Dec 15, 2010 at 11:35:32AM -0700, Carl Sorensen wrote:
> On 12/15/10 9:29 AM, "Juha Erkkila" <address@hidden> wrote:
> > Is it possible to define functions that generate music functions
> > in Lilypond?  I'm looking something to this effect:
> > 
> > -----
> > \version "2.12.3"
> > 
> > musicA = #(define-music-function (parser location music)
> >                                  (ly:music?)
> >            #{ c4 d e f $music #})
> > 
> > \musicA { g4 a b a }
> > 
> > % makeMusicFn = #(define-music-function (parser location prepend-music)
> > %                                       (ly:music?)
> > %                 (define-music-function (parser location append-music)
> > %                                        (ly:music?)
> > %                  #{ $prepend-music $append-music #}))
> > %
> > % musicB = \makeMusicFn { c4 d e f }
> > %
> > % \musicB { g4 a b a }
> > -----
> > 
> > Here expressions "\musicA { g4 a b a }" and "\musicB { g4 a b a }"
> > should evaluate to same music expression, that is
> > { c4 d e f g4 a b a }.  The expressions that are commented out are
> > attempts to achieve what I'm looking for.  The above syntax is,
> > however, wrong, as define-music-function must return a music
> > expression, not a function.
> 
> Music functions must return music expressions, but scheme functions can
> return functions.
> 
> Are you after this specific behavior, or some other behavior, of which this
> is a simplified example?

The above was just a simplified example, the actual case I try to
do is more complex.  Anyway, this solution is enough for me:

-----
\version "2.12.3"

musicA = #(define-music-function (parser location music)
                                 (ly:music?)
           #{ c4 d e f $music #})

\musicA { g4 a b a }

#(define (musicFn prepend-music)
   (ly:make-music-function (list ly:music?)
                           (lambda (parser location append-music)
                             #{ $prepend-music $append-music #})))


musicB = #(musicFn #{ c4 d e f #})

\musicB { g4 a b a }
-----

Thanks for the tips.  It's good to see scheme and lilypond play
together so nicely!

Juha