Re: Optional arguments for scheme functions

[Thomas Morley]

Am So., 26. Apr. 2020 um 02:35 Uhr schrieb Fr. Samuel Springuel
<address@hidden>:
>
> I’m trying to write a music function in scheme in which the first argument is 
> optional and have run into something that confuses me:
>
> The following works:
>
> \version "2.19.84"
>
> recite = #(define-music-function (times note) ((integer? 1) ly:music?)
>                    #{ \repeat unfold #times { #note }
>                    #})
>
> \new Staff {
>     \new Voice { g' \recite g' g' }
> }
>
> However, when I swap integer? for positive? (to reflect the fact that only a 
> positive integer should be acceptable) it breaks, telling me the argument at 
> position 1 is of the wrong type (it’s music, not a positive number).  Why 
> doesn’t scheme’s handling of optional arguments work when using the positive? 
> predicate?
>

I've no clue why positive? fails here.
Though, for integers >= 0 we have the index? predicate, which works in
your function.


Cheers,
  Harm