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

[Jan-Peter Voigt]

Hi Urs,

just one pointer on Davids message (thank you!): in my example the code 
has to be a singular expression, which is the case in most of my cases 
where I use let or begin. If you want to use more than one statement use 
the optional-argument-dot (define-my-custom-function . code) and unquote 
splice ,@code

Jan-Peter

Am 20.06.2018 um 11:42 schrieb Urs Liska:
> Hi Jan-Peter,
>
> thanks for the quick response!
>
>
> Am 20.06.2018 um 11:35 schrieb Jan-Peter Voigt:
> > Hi Urs,
> >
> > define-macro is the method you are looking for:
>
> Indeed, that's what I need.
> I might have managed to look that up myself, but I think that with the 
> quoting stuff in place it would have driven me crazy before I'd reached 
> anything ;-)
>
> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> > \version "2.19.80"
> >
> > % define macro
> > #(define-macro (define-my-custom-function code)
> >     ; all wrapping code is (semi)quoted
> >    `(define-music-function
> >      (mus)(ly:music?)
> >      (let*
> >       ((elts (ly:music-property mus 'elements))
> >        (cnt (length elts)))
> >
> >       ,code ; insert (unquoted) user generated code
> >
> >       mus)))
> >
> >
> > % use macro
> > myFunc =
> > #(define-my-custom-function
> >    (ly:message "The music has ~a elements" cnt))
> >
> > % use function
> > {
> >   \myFunc { c' e' }
> > }
> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> >
> > HTH
>
> It does, and I think I can go from here myself.
>
> Thanks
> Urs
>
> > Jan-Peter
> >
> > Am 20.06.2018 um 11:18 schrieb Urs Liska:
> > > I'm providing users with the option to configure some behaviour by 
> > > providing custom styling functions. These functions must have a 
> > > certain interface and will typically retrieve the same information 
> > > from their arguments. I would like to simplify this task by providing 
> > > a "function template". I think this may be achieved by macros or some 
> > > other syntactic extension mechansim, but I have no idea about how to 
> > > go forward with that.
> > >
> > > This is what currently a user would have to do:
> > >
> > > \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.
> > >
> > > Is this possible? I would assume so, and I'd also would assume it's 
> > > quite easy - once you know what to look for.
> > >
> > > Thanks
> > > Urs
> > >
> > >
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> >
> >
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