George Caswell <tetsu...@maine.rr.com> writes:
>    Anyway, my implementation, "subs" uses up a lot of heap space compared to,
> say, "combos" posted by John Stone, and incurs more garbage collection, but
> still comes out faster:

> (define (expand xs sets)
>     (if (or (null? xs) (null? sets))
>         ()
>    (cons
>        (apply append (map (lambda (set) (map (lambda (s) (cons (car xs)
> s)) set)) (cdr sets)))
>        (expand (cdr xs) (cdr sets)))
> ))

> (define (subs xs n)
>     (cond ((eq? 0 n) ())
>         (else
>        (do ((i 1 (+ i 1))
>             (acc (map (lambda (x) (list (list x))) xs) (expand xs acc)))
>            ((= i n) (apply append acc))))))