Am 14.01.2015 um 12:42 schrieb Mattes:
Am Mittwoch, 14. Januar 2015 12:34 CET, Urs Liska <u...@openlilylib.org>
schrieb:
#(define (annotation? obj)
(and
(list? obj)
(every pair? obj)
(if (assoc-ref obj "type") #t #f)
(if (assoc-ref obj "location") #t #f)))
... and is this just equivalent to:
#(define (annotation? obj)
(and
(list? obj)
(every pair? obj)
(assoc-ref obj "type")
(assoc-ref obj "location")))
???
I don't think so because the result of the function would be the result
of the last expression.
assoc-ref returns the "value" to the "key", so if passed a valid object
the result of the predicate wouldn't be #t but the content of "location".
That's why I enclosed these checks in if constructs.
Richard is right, the if-clauses aren't neccessary. Scheme has the
concept "generalized" booleans, i.e. anything that isn't explicitly
false is considered to be true:
guile> (if 42 'true 'false)
I was just trying to keep as much of your code as possible ....
Cheers, RalfD
OK, I see.
But somehow it feels wrong that
#(display annotation? some-obj)
doesn't produce #t but the content of "location".
Should I ignore that feeling?
Urs
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