Re: How to create a music function properly?

[Marc Hohl]

David Kastrup schrieb:
> Marc Hohl <address@hidden> writes:
>
>   
> > Hello list,
> >
> > after having written mails way too early to this list recently
> > while overlooking the obvious, I think I stumbled upon a *real*
> > problem now :-/
> >
> > Please have a look at the attached file. This is not the real world problem,
> > but I boiled it down to a nearly minimal example.
> >
> > Only version 3 is giving the desired output in standard notation,
> > but ignoring the \override.
> >
> > What am I doing wrong here?
> >
> > Thanks in advance!
> >
> > Marc
> >
> > \version "2.13.32"
> >
> > % thanks to Neil for this function
> > #(define (make-harmonic mus)
> >   (let ((elts (ly:music-property mus 'elements))
> >         (elt (ly:music-property mus 'element)))
> >        (cond
> >         ((pair? elts)
> >          (map make-harmonic elts))
> >         ((ly:music? elt)
> >          (make-harmonic elt))
> >         ((music-is-of-type? mus 'note-event)
> >          (set! (ly:music-property mus 'articulations)
> >                (append
> >                  (ly:music-property mus 'articulations)
> >                  (list (make-music 'HarmonicEvent))))))
> >        mus))
> >
> >
> > harmonicTestOne = #(define-music-function (parser location music) (ly:music?)
> >   (let* ((test 2)
> >          (result (/ test 2)))
> >
> >   #{
> >     \override TabNoteHead #'transparent = ##t
> >   #}
> >   (make-harmonic music)
> >   (display "\nDummy output to check the let-block: ")(display result)
> >   #{
> >     \revert TabNoteHead #'transparent
> >   #}))
> >     
>
>   
Hi David,

> Uh, #{ #} creates and returns a value.  Only the last value in a Scheme
> function is the return value of the function.
>   
I thought I had memorized that, but the whole #{ ...#} stuff
confused me.
> [...]
> Uh, you need $result here, or the global result will be used.  Also, a #
> expression is evaluated when it is encountered.  That may be before the
> \override is considered complete.
>
>   
> >   [...]
> You don't return your override as the resulting music function
> expression.  Expressions in #{ ... #} don't "happen" when encountered.
> They "happen" by returning them to the music function caller.  So the #{
> #} is a do-nothing here.
>   
Thanks for your explanations - if I had a simple scheme-ish
method at hand to do the override and revert, then it would
have been easier for me, I assume. No, probably not. The
return code would have been still the revert ... ;-)

Marc