Instead of passing a string directly as the first argument to `regexp-match`, use `regexp` to convert the string to a regexp value if you want to use it multiple times.
Changing (define (matches rx lstr) (filter (λ(w)(regexp-match? rx w)) lstr)) to (define (matches rx-str lstr) (define rx (regexp rx-str)) (filter (λ(w)(regexp-match? rx w)) lstr)) makes the "regexp-golf-racket.rkt" example take 3 seconds on my machine instead of 50 seconds. Similarly, mapping `regexp` over the right-hand side of `lrx` in "regex-timing.rkt" makes it take less than 1 second instead of 25 seconds. I think Python similarly converts strings to regexps, but it internally caches the conversion. At Thu, 26 Jun 2014 18:19:51 +0200, Laurent wrote: > Hi, > > While translating (almost literally) Norvig's awesome regex golf from > Python [1] to Racket [2], I'm facing a 25x slowdown (about 2s vs 50s). I've > run the optimization coach and made the obvious changes (mainly adding > `in-list` in `for` loops), tried to optimize `filter` and cache the regexps > in a hash (to avoid their recompilation, since I need to keep the raw > string too), but with no significant gain. > > Reading the profile report, it seems that most of the time (99%) is spent > in `regexp-match`, so I wanted to write a stripped down version showing > that Python indeed is much faster than Racket on this particular function > but this test case shows almost the contrary! (25s vs 23s) > > So I'm stumped and I have no idea how to cut this 25x slowdown. Does anyone > have an idea? > > In [2], you can find: > - the regex golf file in Python (used for timing), which is almost > identical to Norvig's > - the translation in Racket > - the stress test of `re.search` in Python > - the stress test of `regexp-match?` in Racket > > Timings can be found at the bottom of each file. > > Note that the outputs of the programs are not exactly the same, because > sets are used in Python and lists in Racket, but unless there are bugs in > my code (which is not improbable) I don't think it matters a lot. > > Thanks, > Laurent > > [1] http://nbviewer.ipython.org/url/norvig.com/ipython/xkcd1313.ipynb > [2] https://gist.github.com/Metaxal/777be153b50a35a2618c > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
