I'm not used to the reply-to begin set to the individual vs. the list for racketusers, so I'll forward a few replies... Begin forwarded message:
> From: Brian Adkins <racketus...@lojic.com> > On Jul 12, 2014, at 1:17 PM, Matthias Felleisen wrote: >> On Jul 12, 2014, at 12:53 PM, Brian Adkins wrote: >> >>> I'm porting more Haskell code to Racket as a learning exercise. When I got >>> to this line: >>> >>> isPos (r,c) = elem r [0..4] && elem c [0..r] >>> >>> I first wrote this: >>> >>> (define (is-pos r c) (and (member r (lgen 0 4)) >>> (member c (lgen 0 r)))) >>> >>> where lgen is: >>> >>> (define (lgen m n) (build-list (+ 1 (- n m)) (λ (x) (+ x m)))) >>> >> >> >> Have you considered turning your Haskell code into prefix and leaving it >> otherwise alone (mostly): > > Not until now :) > >> >> #lang racket >> >> ;; >> ----------------------------------------------------------------------------- >> ;; prelude >> >> (module+ test (require rackunit)) >> >> (define-syntax-rule >> (= (f x ...) expression) >> (define (f x ...) expression)) >> >> (define (.. low high) (range low high)) >> (define (elem r rng) (cons? (member r rng))) >> >> ;; >> ----------------------------------------------------------------------------- >> ;; Haskell to Racket >> ;; isPos (r,c) = elem r [0..4] && elem c [0..r] >> >> ((isPos r c) . = . (and (elem r [.. 0 4]) (elem c [.. 0 r]))) > > Wow, interesting idea. I wasn't sure what ". = ." was, so I just tried '(7 . > 8 . 9) in the repl and got '(8 7 9); apparently the above gets converted to: > > (= (isPos r c) (and (elem r [.. 0 4]) (elem c [.. 0 r]))) > > It took a while to find: > > "Such a pair triggers a reader conversion that moves the element between .s > to the front of the list. The conversion enables a kind of general infix > notation:" on: > > http://docs.racket-lang.org/guide/Pairs__Lists__and_Racket_Syntax.html > > searching about . is challenging. > > Thanks for the "range" tip. I did some googling and didn't find anything so I > resorted to lgen; I should've known that Racket would provide a decent > built-in. > > Not sure how I feel about [.. 0 4] yet vs. (range 0 5). My goal isn't to get > my code to the concise level that Haskell provides, just to get rid of extra > fluff at times. > > Also (lgen m n) is (range m (add1 n)). It seems odd to me that (range 2 4) > generates '(2 3). Is that an historical artifact? > > The Haskell version of isPos accepts a single 2-tuple argument, so I think a > list or struct is closer to the original than separate args. I've modified my > code to use a struct for now, I'll see how that works. The defpat macro > accepts a struct constructor as is, so that's handy. > > >> >> ;; >> ----------------------------------------------------------------------------- >> ;; some tests >> >> (module+ test >> (check-true (isPos 1 0)) >> (check-true (isPos 2 1)) >> (check-false (isPos 1 2)) >> (check-false (isPos 5 1))) >> >> >> >> Okay, the line is still a bit wider but that's because of extra spaces -- >> Matthias >> >> > ____________________ Racket Users list: http://lists.racket-lang.org/users
