Re: SVG export - how might you add classes for all graphical objects?

[Aaron Hill]

On 2021-06-29 1:20 pm, David Kastrup wrote:
> > %%%%
> > \version "2.22.0"
> >
> > SvgAddClassName =
> > #(lambda (ctxt)
> >   (define (add-class-name grob)
> >    (let* ((attribs (ly:grob-property grob 'output-attributes '()))
> >           (class (ly:assoc-get 'class attribs '()))
> >           (name (grob::name grob)))
> >     (set! class (if (null? class) name (format #f "~a ~a" class 
> > name)))
> >     (set! attribs (assoc-set! attribs 'class class))
> >     (ly:grob-set-property! grob 'output-attributes attribs)))
> >   (make-engraver
> >    (acknowledgers
> >     ((grob-interface engraver grob source)
> >      (add-class-name grob)))))
>
> That assoc-set! looks like a stinker.  Doesn't it mess with shared data
> structures?

Hrm... would it be better to explicitly alist-copy the result from 
ly:assoc-get?  Actually, I guess you could do:

;;;;
(alist-cons 'class ... (alist-delete 'class attribs))
;;;;

...since the SRFI says that alist-delete does not modify the original 
structure, only that it might return an alist with a common tail.

And on this point, should LilyPond provide an ly:assoc-set to pair with 
ly:assoc-get that avoids potential issues with shared structures?


-- Aaron Hill