Re: How to create a music function properly?

[Marc Hohl]

Neil Puttock schrieb:
> On 27 September 2010 20:02, Marc Hohl <address@hidden> wrote:
>
>   
> > 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 Neil,
> This swallows the music, since the (make-harmonic music) part isn't
> last in the list: it returns the \revert only.
>
>   
why are solutions ever so simple? Argh, I must have seen that.
Thanks for your patience.
> > harmonicTestTwo = #(define-music-function (parser location music)
> > (ly:music?)
> >  (let* ((test 4)
> >         (result (/ test 2)))
> >  #{
> >    \override TabNoteHead #'transparent = ##t
> >
> >  #(begin
> >     (display "\nDummy output to check the let-block: ")
> >     (display result)
> >     (make-harmonic $music))
> >    \revert TabNoteHead #'transparent
> >  #}))
> >     
>
> Here the \override and \revert are both included, since the #{ #}
> block creates a sequential music section.  Unfortunately, the
> (make-harmonic music) part never gets processed by the parser: as a
> scheme object, it's ignored unless treated like an identifier via
> `ly:export'.  It can't be part of the `begin' in this case.
>   
Ok, this is/was beyond my actual scheme (and lilypond's internals)
knowledge.
> harmonicTestTwo =
> #(define-music-function (parser location music) (ly:music?)
>    (let* ((test 4)
>           (result (/ test 2)))
>      #{
>        \override TabNoteHead #'transparent = ##t
>        #(begin
>          (display "\nDummy output to check the let-block: ")
>          (display $result))
>        #(ly:export (make-harmonic $music))
>        \revert TabNoteHead #'transparent
>      #}))
>
>   
> > harmonicTestThree = #(define-music-function (parser location music)
> > (ly:music?)
> >  (let* ((test 6)
> >         (result (/ test 2)))
> >
> >  #{
> >    \override TabNoteHead #'transparent = ##t
> >  #}
> >  (begin
> >     (display "\nDummy output to check the let-block: ")
> >     (display result)
> >     (make-harmonic music))))
> >     
>
> You're on the right track here: now you're actually returning the
> correct music, but it's also junking the \override, since it's not
> part of the returned music.  If you wrap it in make-sequential-music,
> both actions will take place in sequence:
>   
The same goes for this example - it sounds totally logical the
way you explain it, but I never had found this myself.
> harmonicTestThree =
> #(define-music-function (parser location music) (ly:music?)
>    (let* ((test 6)
>           (result (/ test 2)))
>      (make-sequential-music
>       (list
>        #{
>          \override TabNoteHead #'transparent = ##t
>        #}
>        (begin
>         (display "\nDummy output to check the let-block: ")
>         (display result)
>         (make-harmonic music))))))
>
> I suggest you stay in scheme for this kind of music function rather
> than switching into lily code (which can't be auto-indented properly).
>
>   
I added the \revert to the list, and it works like a charm!

Thanks for your detailed explanations!

Marc