Re: Slurs in scheme?

[Trevor Bača]

On 9/8/05, Nicolas Sceaux <address@hidden> wrote:
> Joe Neeman <address@hidden> writes:
> 
> > As a simple example, here I'm trying to write a function that expands
> > "a" into something like "a( a)":
> >
> > slur =
> > #(def-music-function
> >   (parser location m)
> >   (ly:music?)
> >
> >   (make-sequential-music
> >     (list
> >       m
> >       (make-span-event 'SlurEvent START)
> >       m
> >       (make-span-event 'SlurEvent STOP))))
> >
> > {
> >     b \slur a
> > }
> >
> > But I don't get the slur in the output. I've also tried similar things
> > with ties and I've tried changing the order of the elements in the
> > list.
> 
> The first thing to do is to see what the music that you want to build
> looks like. You use \displayMusic :
> 
>   \displayMusic { a' ( a' ) }
> ==>
> (make-music
>   'SequentialMusic
>   'elements
>   (list (make-music
>           'EventChord
>           'elements
>           (list (make-music
>                   'NoteEvent
>                   'duration
>                   (ly:make-duration 2 0 1 1)
>                   'pitch
>                   (ly:make-pitch 0 5 0))
>                 (make-music
>                   'SlurEvent
>                   'span-direction
>                   -1)))
>         (make-music
>           'EventChord
>           'elements
>           (list (make-music
>                   'NoteEvent
>                   'duration
>                   (ly:make-duration 2 0 1 1)
>                   'pitch
>                   (ly:make-pitch 0 5 0))
>                 (make-music
>                   'SlurEvent
>                   'span-direction
>                   1)))))
> 
> So the bad news here is that the SlurEvent expressions have to be added
> "inside" the note that you want to give has an argument (more precisely,
> the EventChord expression).
> 
> The argument to the function will look like that:
> 
>   \displayMusic a'
> ==>
> (make-music
>   'EventChord
>   'elements
>   (list (make-music
>           'NoteEvent
>           'duration
>           (ly:make-duration 2 0 1 1)
>           'pitch
>           (ly:make-pitch 0 5 0))))
> 
> So, in the function, you'll want to clone this expression (so that you
> have two notes to build the sequence), add SlurEvents to the 'elements
> property of each ones, and finally make a SequentialMusic with the two
> EventChords.
> 
> 
> slur = #(def-music-function (parser location note) (ly:music?)
>          "Return: { note ( note ) }.
> `note' is supposed to be an EventChord."
>          (let ((note2 (ly:music-deep-copy note)))
>            (set! (ly:music-property note 'elements)
>                  (cons (make-music 'SlurEvent 'span-direction -1)
>                        (ly:music-property note 'elements)))
>            (set! (ly:music-property note2 'elements)
>                  (cons (make-music 'SlurEvent 'span-direction 1)
>                        (ly:music-property note2 'elements)))
>            (make-music 'SequentialMusic 'elements (list note note2))))
> 
> \displayMusic \slur a'
> 
> ==>
> (make-music
>   'SequentialMusic
>   'elements
>   (list (make-music
>           'EventChord
>           'elements
>           (list (make-music
>                   'SlurEvent
>                   'span-direction
>                   -1)
>                 (make-music
>                   'NoteEvent
>                   'duration
>                   (ly:make-duration 2 0 1 1)
>                   'pitch
>                   (ly:make-pitch 0 5 0))))
>         (make-music
>           'EventChord
>           'elements
>           (list (make-music
>                   'SlurEvent
>                   'span-direction
>                   1)
>                 (make-music
>                   'NoteEvent
>                   'duration
>                   (ly:make-duration 2 0 1 1)
>                   'pitch
>                   (ly:make-pitch 0 5 0))))))
> 

Wow. I hadn't had time to check out \displayMusic, but how incredibly useful.

Thanks, Nicolas for giving us all such a nice tool to get closer to
the program internals.

-- 
Trevor Bača
address@hidden