Re: Iterators in Scheme?

[Niols]

Hello again,

> 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.

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?

If anyone has any idea on the topic, it would be really useful. In any 
case, I am quite interested in understanding how the execution works and 
thus where LilyPond finds the definition of "\repeat", since it is not 
where I was expecting it.

Thank you in advance, and thank you for your time!
— Niols