It looks to me like the slowdown isn't entirely explained by contract
checking, or perhaps TR isn't generating the contracts I would have
guessed. With the program below, I see this output
cpu time: 1228 real time: 1228 gc time: 133
cpu time: 658 real time: 658 gc time: 18
cpu time: 80 real time: 81 gc time: 0
but would have expected the first two lines to be nearly the same.
Robby
#lang racket
(require (only-in math/number-theory divides?))
(define (divisible-by? x d)
(= (modulo x d)
0))
(module d racket/base
(require racket/contract/base)
(define (divisible-by? x d)
(= (modulo x d)
0))
(provide
(contract-out
[divisible-by? (-> exact-integer? exact-integer? boolean?)])))
(require (prefix-in c: (submod "." d)))
(module+ main
(time
(for ([x (in-range 3 5000000)])
(if (3 . divides? . x)
x
0)))
(time
(for ([x (in-range 3 5000000)])
(if (3 . c:divisible-by? . x)
x
0)))
(time
(for ([x (in-range 3 5000000)])
(if (x . divisible-by? . 3)
x
0))))
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