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Re: some suggestions
>>>>> "Matze" == Matthias Neubauer <neubauer@xxxxxxxxxxxxxxxxxxxxxxxxxx> writes:
Matze> Another example is the definition of STREAM-FILTER. Suppose you have a
Matze> non-leaking implementation of STREAM-DROP-UNTIL at hand , the
Matze> following simple definition of STREAM-FILTER should (hopfully) also
Matze> make sense:
Matze> (define (stream-filter pred? stream)
Matze> (stream-unfold (lambda (stream)
Matze> (let ((stream-1 (stream-drop-until pred? stream)))
Matze> (cons (stream-car stream-1)
Matze> (stream-cdr stream-1))))
Matze> Here the "state" that is passed from step to step is the remainder of
Matze> the original stream that still has to be processed for the next
Matze> element. The actual processing in each step is then performed by
Matze> calling STREAM-DROP-UNTIL.
Matze>  Which isn't the case with the current reference implementation I
Matze> just realized. Your STREAM-DROP-UNTIL bares the same space problems as
Matze> the naive STREAM-FILTER implementation does.
Your code above leaks space even if STREAM-DROP-UNTIL doesn't: the
closure handed out to STREAM-UNFOLD holds a reference to STREAM.
This isn't just a nitpick: I think it shows that using STREAM-UNFOLD
doesn't gain you as much simplicity as you might would expect. This
doesn't add anything to the STREAM-UNFOLD vs. STREAM-ITERATE debate of