Re: How to pass a fraction as a parameter for a Scheme function

[Aaron Hill]

On 2020-06-09 12:43 pm, Paolo Prete wrote:
> Hello,
>
> I don't understand how to use a fraction as a parameter for a scheme
> function. More specifically, this gives me an error:
>
> %%%%%%%%%%%%
>
> proportionalNotationDur = #(define-music-function (parser location 
> frac)
> (scheme?)                          #{ \set
> Score.proportionalNotationDuration = #(ly:make-moment frac) #})
> {
>   \proportionalNotationDur 1/16
>   c' c' c' c'
> }
>
> %%%%%%%%%%%%

You should use the fraction? type predicate if you want to accept 1/16 
for input.  The resulting value is a pair with the numerator as the car 
and the denominator as the cdr.

Alternately, you can use the rational? type predicate so the value is 
numeric.  However, you will then need to use Scheme syntax for the 
input: #1/16 instead of 1/16.


-- Aaron Hill