Ricardo Wurmus <ricardo.wur...@mdc-berlin.de> skribis:
> Ludovic Courtès <l...@gnu.org> writes:
[...]
>> In theory it would be possible to do something like:
>>
>> (define (description->package repo meta)
>> (stream-cons `(package …)
>> (stream-unfold (lambda (state)
>> (description->package
>> repo
>> (first-dependency state)))
>> (lambda (state)
>> (done? state))
>> (lambda (state)
>> (next-dependency state))
>> (make-state propagate (setq)))))
>>
>> … where the state is roughly a pair containing the list of next
>> dependencies and the set of already visited dependencies (to avoid
>> duplicates).
>
> That’s a good hint. “stream-unfold” makes my head spin, to be honest.
I had that feeling when I first met ‘unfold’, but my head has kept
spinning since then so I’m fine. ;-)
Here’s an example that should probably be added to the Guile manual:
--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> ,use(srfi srfi-1)
scheme@(guile-user)> (unfold (lambda (x) (> x 10))
(lambda (x) (* 2 x))
1+
0)
$2 = (0 2 4 6 8 10 12 14 16 18 20)
--8<---------------cut here---------------end--------------->8---
Ludo’.
