2014-06-05 15:12 GMT+02:00 Paul Morris <p...@paulwmorris.com>:
> Thomas Morley-2 wrote
[...]
>> And really hackish is:
>>
>> test =
>> #(define-music-function (parser location test-arg mus)
>> (
>> ;very bad, kludgy and hacky, though valid:
>> ((lambda (x) (or (boolean? x) (number? x) (procedure? x))) "")
>> ;scheme?
>> ly:music?
>> )
>>
>> (cond ((boolean? test-arg)
>> (format #t "\n~a is a boolean." test-arg))
>> ((number? test-arg)
>> (format #t "\n~a is a number." test-arg))
>> ((procedure? test-arg)
>> (format #t "\n~a is a procedure." test-arg))
>> (else #f))
>> mus)
>>
>> m = { c''1 }
>>
>> \test ##f \m
>> \test #3 \m
>> \test #(lambda (a) a) \m
>
> Good point about "scheme?", although it is so general that it doesn't tell
> you which combination of types are expected, while this does:
>
> ((lambda (x) (or (boolean? x) (number? x) (procedure? x))) "")
>
> I'm not sure I understand why this is so bad. It seems better than
> "scheme?" here since it is more specific. I had tried to do this before but
> I didn't know I needed to include the "" at the end. (I assume this "" is
> the description and could be changed to "boolean, number, or procedure" so
> error messages would be accurate.)
No.
It abuses the syntax for an _optional_ argument, with the default ""
Look at:
testII =
#(define-music-function (parser location test-arg mus)
(
;very bad, kludgy and hacky, though valid:
((lambda (x) (or (boolean? x) (number? x) (procedure? x))) "xy")
;scheme?
ly:music?
)
(format #t "\nThe default for \"test-arg\" is ~a." test-arg)
mus)
m = { c''1 }
\testII \m
Cheers,
Harm
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