Re: question about overrides within repeats

[David Kastrup]

David Nalesnik <address@hidden> writes:

> Hi,
>
> Given the following function, each time an override of NoteHead.color
> occurs, a new color from the list is used:
>
> \version "2.19.30"
>
> #(define test
>    (let ((colors (circular-list red green blue yellow darkgreen magenta)))
>      (lambda ()
>        (let ((color (car colors)))
>          (set! colors (cdr colors))
>          color))))
>
> {
>   \once\override NoteHead.color = #(test)
>   c''4
>   \once\override NoteHead.color = #(test)
>   c''4

> However, when I put the override within a repeat structure, the override
> only seems to happen once:
>
> %% All darkgreen (we left off with yellow above
> {
>   \repeat unfold 10 {
>     \once \override NoteHead.color = #(test)
>     c''4
>   }
> }
>
> Is there any way to get the override to be reevaluated with each repeat?

No.  Written in that manner, the override is evaluated at _input_ time.
If you put it in a variable and use that variable 3 times, the colors
will be the same each time.  What you want is

#(define test
   (let ((colors (circular-list red green blue yellow darkgreen magenta)))
     (lambda (grob)
       (let ((color (car colors)))
         (set! colors (cdr colors))
         color))))

and

  \override NoteHead.color = #test

That way you'll get one call per actual _grob_ since then each grob is
then initialized with the callback, and the callback is replaced by the
value when the property is first used.

-- 
David Kastrup