On Thu, Mar 2, 2017 at 12:15 PM, David Storrs <david.sto...@gmail.com>
> On Thu, Mar 2, 2017 at 11:22 AM, David Christiansen <
> da...@davidchristiansen.dk> wrote:
>> > Not with map, which requires equal-length arguments.
>> > You could do the slightly less ugly:
>> > (map
>> > foo
>> > lst-A
>> > lst-B
>> > (range (length lst-A)))
>> Why not do it this way?
>> (struct foo (a b c))
>> (define lst-A '(a b))
>> (define lst-B '(d e))
>> (for/list ([a (in-list lst-A)]
>> [b (in-list lst-B)]
>> [n (in-naturals)])
>> (foo a b n))
>> This seems to be the nicest of the lot.
> I could, it's just extremely more verbose and therefore obfuscates what's
> actually going on as compared to the 'map' form.
> The issue with streams and sequences not being iterable in some cases has
> tripped me up several times. I confess I don't understand the design
> decisions behind them. Can someone ELI5 for me about what exactly they are
> and why they work the way they do / aren't interchangeable? From a naive
> perspective it seems like it would be possible to make them work smoothly
> together by adding a "cond: choose the right iterator func based on the
> type" under the hood. Something like the following, except this is
> probably very slow and I'd need to figure out the appropriate generation
> for the '(choose-iter sourceN)' lines:
> (define-syntax relaxed-map
> (syntax-case stx ()
> [(_ func source1 source2 ...)
> (let ()
> (define (choose-iter x)
> (cond [(list? x) (list list-ref x)]
> [(stream? x) (list stream-ref x)]
> [(sequence? x) (list sequence-ref x)]))
> (for/list ((i (in-range (add1 (min (map length source1 source2
> (list ((choose-iter source1) source1 i)
> ((choose-iter source2) source2 i)
> ...)))])) ;; This won't actually generate the 'choose-iter'
> lines properly
Also, that needs to be '(apply min (map ...' Still, you get the point.
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