Re: Iterators in Scheme?

[Niols]

Hello again,

On 30/07/2020 18:22, Niols wrote:
> > On 29/07/2020 17:28, Jean-Julien Fleck wrote:
> > > Le mer. 29 juil. 2020 à 15:44, Niols <niols@niols.fr 
> > > <mailto:niols@niols.fr>> a écrit :
> > >
> > >
> > >      > What do you want to achieve?
> > >
> > >     This is actually follow-up research from my side after a previous
> > >     e-mail
> > >     to this list. I would like to print bar numbers that are "repeat
> > >     aware",
> > >     that is such that if bars 9 to 12 repeat twice, then the bar 
> > > numbers go
> > >
> > >           1, 2, …, 9, …, 12, 17, 18, etc.
> > >
> > >     with a jump after 12 that corresponds to the bars 13 to 16 that are
> > >     actually 9 to 12. Even better, I would like to print the two bar
> > >     numbers
> > >     for these bars (9/13, 10/14, etc.)
> > >
> > >
> > > Perhaps this snippet could be of some use for you: 
> > > http://lsr.di.unimi.it/LSR/Item?id=1080
>
> I have been playing with this solution and I find it very satisfactory 
> for my use. I do not understand yet all the intrinsics (in particular 
> with respect to the context-spec-music and the make-apply-context 
> functions), but I understand roughly how it works.
>
> There is just one thing that I would want to "improve" (that is, for my 
> use): the solution needs to map on all the music in order to find all 
> the VoltaRepeatedMusic and override their callbacks to a newly defined 
> one. This is achieved by providing a function "unfoldBarNumbers" that 
> can be applied to any music and that does it.
>
> I would however be interested to have that for all the music in my file, 
> without having to call that function. The different ideas that pop into 
> my mind in such a situation are the following:
>
> 1. Maybe I could override the "\repeat" function so that it does the 
> same thing as by default but, when it is a "volta" repeat, it also 
> attaches the new callback to the created music. I believe I see how to 
> achieve that, except I seem unsuccessful in overriding the default 
> definition of "\repeat". Even if I do something like:
>
>      #(define (repeat type num body alts)
>        (display "\nrepeat\n"))
>
>      { b4 \repeat volta 2 { b b } b }
>
> it behaves as if I had not put the #(define ...) statement. I have 
> played around this idea for a while without success. I have tried to see 
> if "\repeat" had a special treatment (which it does, at least in the 
> lexing/parsing), but I haven't been able to figure this out.

I have not managed to override the "\repeat" music function. I suspect 
there is something I do not understand in the order in which things are 
executed in LilyPond.

I have however found a solution based on overriding "make-music". I 
replace "make-music" by a wrapper around it that adds the callback from 
the snippet to all 'VoltaRepeatedMusic and leaves the rest alone. This 
is actually just a few lines:

    #(define the-make-music make-music)

    #(define (make-music-wrapped name . music-properties)
      (let ((music (apply the-make-music (cons name music-properties))))
       (if (equal? name 'VoltaRepeatedMusic)
        (ly:music-set-property! music 'elements-callback new-volta-set))
       music))

    #(set! make-music make-music-wrapped)

It might not be the cleanest, but that is all I have, and that seems to 
work.

> 2. Maybe there is a way to define a function that will be ran before 
> processing on any music? But this I have no idea if this is possible, or 
> how to do it, and my research has proven ineffective so far.
>
> 3. Maybe there is a way to override the "make-volta-set" callback 
> instead of creating a new one? Such that then, in LilyPond's normal 
> execution, it uses the new definition and not and old one that then 
> needs to be replaced?

For 2. and 3., I still have no idea as this is far beyond my 
understanding of the internals of LilyPond. I am not really looking into 
it though.

Thank you for your help; have a great Summer!
— Niols