Re: Passing a parameter to Scheme

[Aaron Hill]

On 2022-10-29 2:50 am, Paul Hodges wrote:
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> speak = {
>   \once \override Stem.stencil =
>     #(lambda (grob)
>        (let* ((x-parent (ly:grob-parent grob X))
>               (is-rest? (ly:grob? (ly:grob-object x-parent 'rest))))
>          (if is-rest?
>              empty-stencil
>              (ly:stencil-combine-at-edge
>               (ly:stem::print grob)
>               Y
>               (- (ly:grob-property grob 'direction))
>               (grob-interpret-markup grob
>                                      (markup #:center-align #:fontsize 
> -2
>                                              #:musicglyph 
> "noteheads.s2cross"))
>               -2.3))))
> }
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> This works fine, writing "\speak c4" for instance.
>
> However, I'd like to be able to parameterise the position of the cross 
> which is hard-coded as -2.3, so that I can write "\speak #-3.8 c" for 
> instance.  I've tried a couple of ways to write it, but I can't find 
> one that works.  I suppose that I will need something like "lambda 
> (grob posn)" to define the parameter for use at the end, but I can't 
> see how to get the value of posn from the LilyPond source into the 
> Scheme procedure.

Review the documentation on defining and using music functions:

[1]: 
https://lilypond.org/doc/v2.23/Documentation/extending/music-functions

You could end up with something like this:

%%%%
speak =
#(define-music-function
  (position)
  (number?)

  (define (stencil-proc grob)
   (let* ((x-parent (ly:grob-parent grob X))
          (is-rest? (ly:grob? (ly:grob-object x-parent 'rest))))
    (if is-rest?
     empty-stencil
     (ly:stencil-combine-at-edge
      (ly:stem::print grob)
      Y
      (- (ly:grob-property grob 'direction))
      (grob-interpret-markup grob
       (markup #:center-align #:fontsize -2
               #:musicglyph "noteheads.s2cross"))
      (- position)))))

  #{ \once \override Stem.stencil = #stencil-proc #})

{
  \speak 1.6 g'4
  \speak 2.2 b'8 8
  \speak 2.8 a'2
}
%%%%


-- Aaron Hill