Re: macro for \once\override

[Aaron Hill]

On 2020-08-29 3:19 am, Wols Lists wrote:
> On 29/08/20 05:45, Werner LEMBERG wrote:
> >       \once \override FretBoard.size = #'1.0
> >       \once \override FretBoard.fret-diagram-details.barre-type = 
> > #'straight
> >       \once \override FretBoard.fret-diagram-details.dot-color = 
> > #'black
> >       \once \override FretBoard.fret-diagram-details.finger-code = 
> > #'below-string
> >       c'
>
> Unfortunately this might well require re-writing the parser, but it
> struck me it might be a nice idea to nick an idea from other object
> oriented languages as follows ...
>
>     \once \override FretBoard.size = #'1.0
>     \once \override \using FretBoard.fret-diagram-details {
>         .barre-type = #'straight
>         .dot-color = #'black
>         .finger-code = #'below-string
>     }
>     c'

No need to rewrite anything.  We can use \with to assist with this 
pattern:

%%%%
overrideII =
#(define-music-function
  (prop mods)
  (key-list? ly:context-mod?)
  (define (assign? mod) (eq? 'assign (car mod)))
  (define (proc mod)
    (let ((subprop (cadr mod))
          (value (caddr mod)))
      #{ \override #prop . #subprop = #value #}))
  #{ #@(map proc (filter assign? (ly:get-context-mods mods))) #})
%%%%

While there is almost certainly a better name than overrideII, it 
permits the following:

%%%%
\once \override FretBoard.fret-diagram-details.barre-type = #'none
\once \override FretBoard.fret-diagram-details.number-type = #'arabic
\once \override FretBoard.fret-diagram-details.orientation = #'landscape
\once \override FretBoard.fret-diagram-details.mute-string = #"M"
\once \override FretBoard.fret-diagram-details.label-dir = #LEFT
\once \override FretBoard.fret-diagram-details.dot-color = #'black
%% ...becomes...
\once \overrideII FretBoard.fret-diagram-details
\with {
  barre-type = #'none
  number-type = #'arabic
  orientation = #'landscape
  mute-string = #"M"
  label-dir = #LEFT
  dot-color = #'black
}
%%%%

-- Aaron Hill