Thanks everyone. I guess I misread the docs. Great to hear re: caching. Guess I wasn't screwing things up as I momentarily feared. :)
Sam Tobin-Hochstadt writes: > Here are some quick numbers on the traditional Racket VM: > > ``` >> (define v (build-list 10000000 values)) >> (time (list? v)) > cpu time: 47 real time: 47 gc time: 0 > #t >> (time (list? v)) > cpu time: 31 real time: 31 gc time: 0 > #t >> (time (list? v)) > cpu time: 13 real time: 13 gc time: 0 > #t >> (time (list? v)) > cpu time: 15 real time: 16 gc time: 0 > #t >> (time (list? v)) > cpu time: 4 real time: 4 gc time: 0 > #t >> (time (list? v)) > cpu time: 1 real time: 1 gc time: 0 > #t >> (time (list? v)) > cpu time: 2 real time: 2 gc time: 0 > #t >> (time (list? v)) > cpu time: 1 real time: 1 gc time: 0 > #t >> (time (list? v)) > cpu time: 1 real time: 0 gc time: 0 > #t >> (time (list? v)) > cpu time: 1 real time: 0 gc time: 0 > #t >> (time (list? v)) > cpu time: 1 real time: 0 gc time: 0 > #t >> (define v2 (drop v (/ 10000000 2) )) >> (time (list? v2)) > cpu time: 0 real time: 0 gc time: 0 > #t > ``` > Here's some RacketCS numbers, which are a little different: > > ``` > [samth@huor:~/.../extra-pkgs/typed-racket/typed-racket-test (master) > plt] racketcs > Welcome to Racket v7.5.0.4 [cs]. >> (define v (build-list 10000000 values)) >> (time (list? v)) > cpu time: 77 real time: 77 gc time: 0 > #t >> (time (list? v)) > cpu time: 73 real time: 73 gc time: 0 > #t >> (time (list? v)) > cpu time: 53 real time: 53 gc time: 0 > #t >> (time (list? v)) > cpu time: 37 real time: 37 gc time: 0 > #t >> (time (list? v)) > cpu time: 25 real time: 25 gc time: 0 > #t >> (time (list? v)) > cpu time: 12 real time: 13 gc time: 0 > #t >> (time (list? v)) > cpu time: 2 real time: 2 gc time: 0 > #t >> (time (list? v)) > cpu time: 3 real time: 3 gc time: 0 > #t >> (time (list? v)) > cpu time: 1 real time: 1 gc time: 0 > #t >> (time (list? v)) > cpu time: 0 real time: 0 gc time: 0 > #t >> (define v2 (drop v (/ 10000000 2) )) >> (time (list? v2)) > cpu time: 61 real time: 61 gc time: 0 > #t >> (time (list? v2)) > cpu time: 50 real time: 50 gc time: 0 > #t >> (time (list? v2)) > cpu time: 15 real time: 15 gc time: 0 > #t >> (time (list? v2)) > cpu time: 25 real time: 25 gc time: 0 > #t >> (time (list? v2)) > cpu time: 22 real time: 22 gc time: 0 > #t >> (time (list? v2)) > cpu time: 3 real time: 3 gc time: 0 > #t >> (time (list? v2)) > cpu time: 0 real time: 0 gc time: 0 > #t > ``` > > If you want to make that match pattern faster, use `cons` or `list-rest`. > > Sam > > On Tue, Oct 29, 2019 at 2:18 PM Alexis King <lexi.lam...@gmail.com> wrote: >> >> > On Oct 29, 2019, at 12:41, Christopher Lemmer Webber >> > <cweb...@dustycloud.org> wrote: >> > >> > But the documentation says that the `list?` predicate is O(n). >> >> I’m not sure where you’re seeing that, but the documentation actually says >> just the opposite. Specifically, it says this: >> >> > This procedure effectively takes constant time due to internal caching (so >> > that any necessary traversals of pairs can in principle count as an extra >> > cost of allocating the pairs). >> >> In other words, `list?` is amortized constant time. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Racket Users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to racket-users+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/racket-users/4E904F54-3605-4964-AC19-EB6617A5D9F7%40gmail.com. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/87k18nxv8c.fsf%40dustycloud.org.
