If you're willing to use vectors, then maybe you're also willing to
use a custom data structure? You could get much better performance
that way. Here's a half-baked example of what I mean. `map-once/h`,
below, returns a (normal list) of hole-lists. ("hole-list" is not a
good name. The offset doesn't really designate a hole in the list, but
the offset where the function should be applied.)
===
#lang racket/base
(require racket/match)
(struct hole-list (xs hole-offset fn))
(define (hole-list-empty? hxs)
(match hxs
[(hole-list (? pair?) _ _) #f]
[_ #t]))
(define (hole-list-nonempty? hxs)
(not (hole-list-empty? hxs)))
(define (hcar hxs)
(match hxs
[(hole-list (cons x _) 0 fn) (fn x)]
[(hole-list (cons x _) _ _) x]))
(define (hcdr hxs)
(match hxs
[(hole-list (cons _ xs) n fn) (hole-list xs (sub1 n) fn)]))
(define-match-expander hcons
(syntax-rules ()
[(_ x xs) (and (? hole-list?)
(? hole-list-nonempty?)
(app hcar x)
(app hcdr xs))]))
(define-match-expander hnull
(syntax-rules ()
[(_) (and (? hole-list?)
(? hole-list-empty?))]))
(define (hole-list->list hxs)
(match hxs
[(hnull) '()]
[(hcons x xs) (cons x (hole-list->list xs))]))
(define (map-once/h fn xs)
(for/list ([i (in-range (length xs))])
(hole-list xs i fn)))
On Fri, Jun 19, 2015 at 4:33 PM, Luke Miles <rashreportl...@gmail.com> wrote:
> I timed all these with `sqr` on a list of 10000 `(random)`.
>
> Luke's (my) first one:
> cpu time: 4706 real time: 4699 gc time: 3673
>
> Luke's second one:
> cpu time: 5401 real time: 5393 gc time: 4136
>
> Jon's first one:
> cpu time: 9734 real time: 9728 gc time: 8007
>
> Jon's second one (tested on a vector of course):
> cpu time: 1198 real time: 1195 gc time: 883
>
> Jens' first one:
> cpu time: 5622 real time: 5618 gc time: 4800
>
> Jens' second one:
> cpu time: 4393 real time: 4391 gc time: 3935
>
>
> I thought Jens' second one would be faster. The vector's results are
> promising.
>
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