On Tue, Jul 11, 2017 at 12:16 AM, Nadeem Abdul Hamid <nad...@acm.org> wrote:
> I'm looking for a general solution. Basically, I thought binding multiple
> id's would have achieved what this does:
>
>> (for/list ([t '((1 2 3) (4 5 6) (7 8 9) (a b c))])
> (match-define (list x y z) t)
> (list x z))
> '((1 3) (4 6) (7 9) (a c))
>
As far as I know, there's nothing built-in that does this, but it's
not hard to build:
(define (in-tuples xs)
(make-do-sequence
(λ ()
(values
(λ (pos)
(apply values (car pos)))
cdr
xs
(λ (pos)
(not (null? pos)))
#f
#f))))
(for/list ([(x y z) (in-tuples '((1 2 3) (4 5 6) (7 8 9) (a b c)))])
(list x z))
;; => '((1 3) (4 6) (7 9) (a c))
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