Urs Liska <li...@openlilylib.org> writes:
> \version "2.19.80"
>
> myFunc =
> #(define-music-function (mus)(ly:music?)
> (let*
> ((elts (ly:music-property mus 'elements))
> (cnt (length elts)))
> (ly:message "The music has ~a elements" cnt)
> mus))
>
> {
> \myFunc { c' e' }
> }
>
> Create a music function with one ly:music? argument and extract some
> information from the music expression (of course this is just an
> example, in the real case it's a custom object attached to the music).
>
> What I would like to have is what define-music-function does here but
> with a pre-set argument list and essentially the let* bindings
> transparently done so that something like this is possible:
>
> userFunc =
> #(define-my-custom-function
> (ly:message "The music has ~a elements" cnt))
>
> where one ly:music? argument is implicitly expected and the bindings
> like 'cnt' have already been prepared.
#(define-macro (define-my-custom-function . body)
`(define-music-function (mus) (ly:music?)
(let*
((elts (ly:music-property mus 'elements))
(cnt (length elts)))
,@body
mus)))
That's what one would call a pretty unhygienic macro since it messes
with a number of symbols/identifiers not specified by the user.
--
David Kastrup
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