Because build-string calls an unknown function 1000 x 100000 times, and an unknown function call is expensive.
Racket could possible collapse all modules and perform additional in-lining optimizations eventually, which may help here. But it doesn't yet. -- Matthias On Aug 3, 2014, at 5:15 AM, Roman Klochkov wrote: > Are higher order function always slow? > > Made small test: > test1 -- unfamous set-in-the-loop accumulating > test2 -- built-in build-string > test3 -- manually written build-string with the same code as in test1 > ---- > (define (test1 n) > (define res (make-string n)) > (for ([i (in-range n)]) > (string-set! res i (integer->char i))) > res) > > (define (test2 n) > (build-string n integer->char)) > > (define (build-string1 n proc) > (define res (make-string n)) > (for ([i (in-range n)]) > (string-set! res i (proc i))) > res) > > (define (test3 n) > (build-string1 n integer->char)) > > (time (for ([i 100000]) (test1 100))) > (time (for ([i 100000]) (test1 100))) > (time (for ([i 100000]) (test1 100))) > (displayln "") > (time (for ([i 100000]) (test2 100))) > (time (for ([i 100000]) (test2 100))) > (time (for ([i 100000]) (test2 100))) > (displayln "") > (time (for ([i 100000]) (test3 100))) > (time (for ([i 100000]) (test3 100))) > (time (for ([i 100000]) (test3 100))) > ---- > Tested on Linux x32 > > $ /usr/racket/bin/racket > Welcome to Racket v6.1. > > (enter! "test") > cpu time: 360 real time: 469 gc time: 64 > cpu time: 212 real time: 209 gc time: 0 > cpu time: 208 real time: 208 gc time: 0 > > cpu time: 400 real time: 402 gc time: 0 > cpu time: 380 real time: 382 gc time: 4 > cpu time: 384 real time: 383 gc time: 0 > > cpu time: 524 real time: 529 gc time: 4 > cpu time: 468 real time: 470 gc time: 8 > cpu time: 412 real time: 414 gc time: 12 > > --- > > So I see, that build-string version is about two times slower, than > set-in-the-loop. Why so much? I expected about 10-20% difference. > > -- > Roman Klochkov > ____________________ > Racket Users list: > http://lists.racket-lang.org/users
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