Re: Scheme predicative types

[Lukas-Fabian Moser]

    Hi Aaron,
> > The three forms
> >         
> >         
> >          * \tempo 4 = 96
> >         
> >          * \tempo Crazy 4 = 260-270
> >         
> >          * \tempo "Sluggishly slow"
> >         
> >         
> >         are hardcoded as variants into the parser. My guess is that this
> >         might
> >         
> >         be hard (or impossible) to accomplish in a music function.
> >         
> >       
>       
>       You just need to be a little creative.
    That's what I hoped would happen. :-) If I understand it correctly,
    both the genius and the drawback of your solution lies in having the
    user write an explicit "\tempo" in order to invoke the parser's
    hard-wired way of dealing with the possible syntax variants, right?
> %%%%
>       
>       \version "2.20.0"
>       
>       
>       #(define (tempo? arg)
>       
>         (and (ly:music? arg)
>       
>              (not (null? (extract-typed-music arg
>       'tempo-change-event)))))
>       
>

Maybe I'm overly cautious, but I'd prefer this to be more specific so that it accepts only actual "\tempo ..."-constructs. For example:

#(use-modules (scm display-lily)) #(define (tempo? arg)   (and (ly:music? arg)        (string-startswith (music->lily-string test) "\\tempo")))

This is probably an awful waste of computing effort, but I liked it better than checking for the kind-of special internal structure of a music _expression_ containing only a \tempo (namely, a sequential-music containing both a TempoChangeEvent and a PropertySet specced to context Score.)

    Lukas