Scratch that, naive memoization doesn't fix it. Will tinker with this more out of curiosity
On Thu, Jan 22, 2015 at 1:23 PM, Jack Firth <jackhfi...@gmail.com> wrote: > Add memoization to fix that > > (define (memo f) > (let ([cache (make-hash)]) > (lambda xs > (hash-ref! cache xs (thunk (apply f xs)))))) > > (define (cumulative-sum xs) > (map (memo (curry foldl + 0)) > (build-list (length xs) > (compose (curry take xs) > add1)))) > > On Thu, Jan 22, 2015 at 11:21 AM, Matthias Felleisen <matth...@ccs.neu.edu > > wrote: > >> >> Consider the performance implications. >> >> >> On Jan 22, 2015, at 1:59 PM, Jack Firth <jackhfi...@gmail.com> wrote: >> >> > If you're using all of racket, here's a way to do it with heavy usage >> of higher order functions >> > >> > #lang racket >> > >> > (define (cumulative-sum xs) >> > (map (curry foldl + 0) >> > (build-list (length xs) >> > (compose (curry take xs) >> > add1)))) >> > >> > On Thu, Jan 22, 2015 at 6:34 AM, Matthias Felleisen < >> matth...@ccs.neu.edu> wrote: >> > >> > #lang racket >> > >> > ;; [Listof Number] -> [Listof Number] >> > ;; given (a b c ...) produce (a (+ a b) (+ a b c) ...) >> > (define (cumulative-sum l #;"final private:" [so-far 0]) >> > (cond >> > [(empty? l) '()] >> > [else (define next (+ so-far (first l))) >> > (cons next (cumulative-sum (rest l) next))])) >> > >> > (module+ main >> > (cumulative-sum '(1 2 3))) >> > >> > ;; The comments are HtDP-style, but the optional entry parameter is not >> available in the teaching languages. >> > >> > >> > On Jan 22, 2015, at 8:53 AM, Alexandr M <rus...@gmail.com> wrote: >> > >> > > Hello, >> > > >> > > I am trying to replicate functionality of this code in Python: >> > > >> > > https://gist.github.com/m-blog/22b7c5d31b3839ffba50#file-cumsum-py >> > > >> > > in Racket without usage of any libraries. >> > > >> > > What would the most optimal / concise way to do it in Racket? >> > > >> > > Thank you. >> > > >> > > -- >> > > Best regards, >> > > Alex >> > > ____________________ >> > > Racket Users list: >> > > http://lists.racket-lang.org/users >> > >> > >> > ____________________ >> > Racket Users list: >> > http://lists.racket-lang.org/users >> > >> >> >
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