Re: Function template (or whatever it's called)

[Urs Liska]

Hi Jan-Peter and David,


Am 20.06.2018 um 12:31 schrieb David Kastrup:
> Urs Liska <address@hidden> writes:
>
> > Am 20.06.2018 um 11:38 schrieb David Kastrup:
> >
> > > #(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.
> > Hm, valid point. But I think it is worth it given the use case (I will
> > experiment and keep your point in mind, though).
> By the way, you'll probably arrive at something like
>
> #(define-macro (define-my-custom-function maybe-doc . body)
>      `(define-music-function (mus) (ly:music?)
>         ,(if (string? maybe-doc) maybe-doc
>                                  "define-my-custom-function was here")
>         (let*
>           ((elts ...
>              ,@(if (string? maybe-doc) body (cons maybe-doc body)))
>
> in order to let the user potentially specify a doc string.

Thanks for your help and explanation. I think I managed to get to a nice 
point that will give users of the package a concise way to define 
styling functions, without having to over and over repeat tedious and 
potentially confusing code. (I'll post a link when it's ready and pushed).
Of course it's "unclean" because it will provide local bindings that are 
totally not obvious from the user code, but I think (now more than 
initially) that with sufficient documentation this is more than worth 
the effort.

Urs
>