Re: Apply a music-function script to all elements of a list

[David Nalesnik]

Hi,

On Wed, May 10, 2017 at 9:31 AM, David Nalesnik
<address@hidden> wrote:
>
>
> On Wed, May 10, 2017 at 9:23 AM, daviau ewen <address@hidden> wrote:
>>
>> Is that okay ?
>> http://lilypond.1069038.n5.nabble.com/file/n203059/incdiato82.ly
>>>
>>>
>
> Yes, thank you.
>

Your original:

% ici on défini les points qu'on fait sur le piano
#(define (make-dot-list l1)
   (if (null? l1)
       empty-stencil
       (ly:stencil-add
          (make-dot (ly:pitch-notename (car l1)))

          )))

OK, your function is intended to return a list of dots, but you only
call make-dot on the first element of the list.

You need to apply make-dot to every element of your pitch list, and
then combine these into a stencil.  To combine stencils, I use reduce:
(Documentation here:
https://www.gnu.org/software/guile/docs/docs-1.8/guile-ref/SRFI_002d1-Fold-and-Map.html#index-append_002dmap-3619).
I found reduce and fold somewhat difficult to grasp at first, but they
definitely repay study.

My rewrite:

#(define (make-dot-list l1)
   (reduce
    ly:stencil-add
    empty-stencil
    (map
     (lambda (dl) (make-dot (ly:pitch-notename dl)))
     l1)))

%%%%%%%%%%%%%

Your original:

#(define-markup-command (complete layout props the-chord)
   (ly:music?)

     (ly:stencil-scale
      ( ly:stencil-add
        (engrave-back)
        (make-dot-list (map (lambda (m) (ly:music-property m 'pitch))
                          (extract-named-music the-chord 'NoteEvent)))
         )
      1
      1))

Here, the error messages are instructive.  The function ly:stencil-add
expects its arguments to be individual stencils, but you are providing
it with *lists* of stencils (the result of calling engrave-back and
make-dot-list--the latter corrected as I show above, of course!)

The solution once again is to first create a list of stencils, then
combine them using reduce:

#(define-markup-command (complete layout props the-chord)
   (ly:music?)
   (ly:stencil-scale
    (reduce
     ly:stencil-add
     empty-stencil
     (cons
      (make-dot-list (map (lambda (m) (ly:music-property m 'pitch))
                       (extract-named-music the-chord 'NoteEvent)))
      (engrave-back)))
    1 1))

%%%%%%

Of course, scaling the stencil to 100% is both axes is a bit redundant!

Another observation: the greenish dots are hard to see.

I've attached the whole file (with some formatting changes that helped
me read it better).

Hope this helps,

David

incdiato82.ly
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