Le 20/03/2021 à 17:04, Linus Björnstam a écrit :
Well, mutating like that is not very common, except for maybe with alists.In which situations are you mutating the list like that? Usually you would build a reverse list using a recursive function and an accumulator, which can be done without set! (which has a boxing overhead).
Mostly to mutate properties of LilyPond's probs (property objects). This works somewhat like Guile's object properties. For example, to add articulations on notes: \version "2.23.1" #(define-macro (prepend! thing lst) `(set! ,lst (cons ,thing ,lst))) addStaccato = #(define-music-function (music) (ly:music?) (map-some-music (lambda (m) (if (music-is-of-type? m 'note-event)(prepend! (make-music 'ArticulationEvent 'articulation-type "staccato")
(ly:music-property m 'articulations)))
#f)
music))
\addStaccato { c'4 d' e'8 f' g' a' }
(Output attached.)
It is also of use in so-called engravers (it's harder
to find a simple use case for these). I guess all of this
is so LilyPond-specific that it suits better in my personal
libraries, and maybe upstream if I see a compelling use
case in the code base.
Thanks!
Jean
\version "2.23.1"
#(define-macro (prepend! thing lst)
`(set! ,lst (cons ,thing ,lst)))
addStaccato =
#(define-music-function (music) (ly:music?)
(map-some-music
(lambda (m)
(if (music-is-of-type? m 'note-event)
(prepend! (make-music 'ArticulationEvent 'articulation-type "staccato")
(ly:music-property m 'articulations)))
#f)
music))
\addStaccato { c'4 d' e'8 f' g' a' }
prepend-example.pdf
Description: Adobe PDF document
