hi,
As part of something I'm working on I want to convert a stream of values
into a stream of pairs of values, e.g.
1 2 3 4
becomes
(1 2) (3 4)
The following seems to work fine:
(define (pairwise-stream astream)
(if (stream-empty? astream)
empty-stream
(stream-cons
(cons
(stream-first astream)
(stream-first (stream-rest astream)))
(pairwise-stream
(stream-rest (stream-rest astream))))))
but I'd like my 2nd or 3rd test to detect a problem with a stream of odd
length and haven't figured out how yet. Here's my attempt (lengths 0 and 2
work fine, length 1 shows a contract violation, but my test doesn't detect
it):
(check-equal?
(stream->list
(pairwise-stream empty-stream))
(stream->list empty-stream))
; hmmm, how to detect this correctly?
;(check-exn
; exn:fail:contract?
; (stream-first
; (pairwise-stream (stream-cons 1 empty-stream))))
(check-equal?
(stream->list (pairwise-stream (stream-cons 1 (stream-cons 2
empty-stream))))
(stream->list (stream-cons (cons 1 2) empty-stream)))
I'd be grateful for advice.
Cheers,
Tim
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