You have hit limitations of the for/fold macros. I wrote an extension for controlling the way values get accumulated, along with post-processing like list reversal. Let me know what you think!
https://github.com/ianj/nifty-macros/tree/master/for-acc -Ian ----- Original Message ----- From: Roman Klochkov <[email protected]> To: [email protected] Sent: Sat, 18 Jan 2014 06:25:10 -0500 (EST) Subject: [racket] Style. for/fold for/list for/lists Where can I find style guide for these for/lists: I have to duplicate values names: (define-values ([(desc-args lengths add-data) (for/lists (desc-args lengths add-data) ([arg (in-list %args)]) ....)) is it ok? Or better (define-values ([(desc-args lengths add-data) (for/lists (a b c) (...) ...)) ? for/fold has no "return" clause. So I have to do (call-with-values (for/fold (acc1 acc2 sum) (...) ...) (lambda (acc1 acc2 sum) (reverse acc1) (reverse acc2) sum)) And for/list doesn't allow to add several items to resulting list in one round. Even with for/fold it gives (reverse (for/fold (acc) ([item (in-list list)]) (values (cons (get-val1 item) (cons (get-val2 item) acc))))) Awful, especially for reading. It is clumsy and unobvious. In Common Lisp iterate I could do (iter (...) (collect (foo) into acc1) (collect (bar) into acc2) (summing ... into sum) (finally (return acc1 acc2 sum))) http://common-lisp.net/project/iterate/doc/index.html Is there something similar? -- Roman Klochkov ____________________ Racket Users list: http://lists.racket-lang.org/users
