RE: Defining new Scheme predicates

[Urs Liska]

Am 7. November 2016 01:20:23 MEZ, schrieb Andrew Bernard <address@hidden>:
>Hi Simon,
>
>Thanks! Exactly perfect. Sometimes the completely obvious escapes me.
>Better
>have another coffee.
>
>Most appreciated.
>
>I suppose of course that to make it a predicate without the preliminary
>let
>block (not that I have any objection to that) one would have to modify
>lilypond internals, which would not be desirable.

Not at all!

Just define your predicate with

#(define (side? obj)
  (if (or (eq? obj 'left)
          (eq? obj 'right))
      #t #f))

and use it like any other procedure. The ? at the end is just a convention, 
predicates are nothing else than procedures taking one argument and returning 
#t or #f.

HTH
Urs

(As with Simon this is untested and written on the mobile)
>
>Andrew
>
>
>
>
>
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