I can't really test what you've posted (no stress-testing code), and you also compare safe versus unsafe accessors, which skews things.
I wanted to follow up apologizing to anyone who tried to use my library. I had not tested it thoroughly enough and didn't realize it does not work outside its own module. I've since fixed this and added the documentation in markdown format (Scribble does some weird extra ```racket additions with markdown that I had to manually remove, too. Dunno what that's about). -Ian ----- Original Message ----- From: "Pierpaolo Bernardi" <[email protected]> To: "J. Ian Johnson" <[email protected]> Cc: "Tim Nelson" <[email protected]>, "users" <[email protected]> Sent: Monday, March 25, 2013 10:42:28 AM GMT -05:00 US/Canada Eastern Subject: Re: [racket] for/hash and for/list: adding nothing, adding more than one thing On Mon, Mar 25, 2013 at 2:41 PM, J. Ian Johnson <[email protected]> wrote: > Let me know how you like my library. I'm thinking of adding some more > ergonomics to it: > 1) support right folds so a for/list-like comprehension has better allocation > behavior. > 2) add a keyword for-clause for starting an inner iteration so you don't have > to do this: > (for ([e0 (in-list l0)] > [e1 (in-list l1)]) > (for ([e2 (in-list l2)] > [e3 (in-list l3)]) > ...body...)) > but instead you can do this: > (for ([e0 (in-list l0)] > [e1 (in-list l1)] > #:start-inner-loop ;; suggest a better name please > [e2 (in-list l2)] > [e3 (in-list l3)]) > ...body...)) IMHO the first form is clearer. I don't see any gain in the second one. > I seem to remember that for* is not equivalent to successive nesting of for > forms, but I can't remember how I reached this conclusion. I have found, in one case, that performance of nested fors is significantly better than a single for*, but I have not investigated the cause. See the code fragment below. Cheers P. (define (risolvi-2 sexomini) (let ((tabella (crea-tabella))) (let fansexomino ((sexomini sexomini)) (cond ((null? sexomini) (eureka tabella)) ((posizione-accettabile? tabella sexomini) (let ((sexomino (unsafe-first sexomini))) (for ((orientazione (in-list sexomino))) (let ((forma (unsafe-first orientazione))) (for ((posizione (in-list (unsafe-rest orientazione)))) (when (compatibile? forma posizione tabella) (let* ((x (posizione-x posizione)) (y (posizione-y posizione)) (v (unsafe-vector-ref tabella x))) (unsafe-vector-set! v y forma) (fansexomino (unsafe-rest sexomini)) (unsafe-vector-set! v y #f)))))))))))) #| ;; risolvi-2 is faster (define (risolvi-3 sexomini) (let ((tabella (crea-tabella))) (let fansexomino ((sexomini sexomini)) (cond ((null? sexomini) (eureka tabella)) ((posizione-accettabile? tabella sexomini) (for* ((sexomino (in-value (first sexomini))) (orientazione (in-list sexomino)) (forma (in-value (first orientazione))) (posizione (in-list (rest orientazione))) #:when (compatibile? forma posizione tabella) (x (in-value (posizione-x posizione))) (y (in-value (posizione-y posizione))) (v (in-value (vector-ref tabella x)))) (vector-set! v y forma) (fansexomino (rest sexomini)) (vector-set! v y #f))))))) |# ____________________ Racket Users list: http://lists.racket-lang.org/users
