On Monday, June 28, 2021 at 10:25:36 PM UTC-4 Sam Tobin-Hochstadt wrote: > On Mon, Jun 28, 2021 at 9:46 PM Jonathan Simpson wrote: > > > > On Sunday, June 27, 2021 at 10:29:55 AM UTC-4 Robby Findler wrote: > >> > >> Replacing ` (~r x #:precision 1)` with `(number->string x)` and ditto > for `y` eliminates the overhead of contracts and brings about another 4x > speedup on my machine. > > > > > > This is because the compiler is able to remove the contract checks, not > because number->string doesn't have a contract, correct? If it is the > compiler, is there any rule of thumb to determine when the compiler will > likely remove the contract checks? Using typed 'for' iterators seems to be > one case that the compiler optimizes, but can we rely on others? > > There are two possible meanings for "contract checks" here. One is > "does it check that it gets the right kind of arguments, and raise an > error if not". In that sense, every function that is not "unsafe" has > contracts, certainly including `number->string`. The other meaning is > "uses the `racket/contract` library". The `~r` function has a contract > in that sense, while `number->string` does not, and that's a > significant source of overhead. On my laptop, just removing the > contract on `~r` in the source of the `racket/format` library speeds > up Bogdan's revised program from 600ms to 200ms. > > Most of the time, the compiler does not remove either kind of contract > check. Sometimes the first kind of contract check can be removed in > the simplest of cases; the second kind is basically never removed by > the compiler. There are other cases where macros can generate code > that omits contract checks, as with the `for` forms when used with > sequence generators like `in-list`, but that is again for simple > checks. > > Sam
Thanks for the reply. I was under the impression that all of the racket provided functions had full racket/contract contracts implemented at the module boundary, which is what I thought was generating errors of the form: --- (number->string "aa") ; number->string: contract violation ; expected: number? ; given: "aa" --- I take it that the contract error above was generated by a lower-level contract then. I've only glanced at contracts, so I assume this is documented somewhere. Is this section of the Reference referring to the simple contracts that you mention? >From https://docs.racket-lang.org/reference/contracts.html: --- Contracts come in two forms: those constructed by the various operations listed in this section of the manual, and various ordinary Racket values that double as contracts, including... --- Once again, thanks for the information. -- Jonathan -- 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/34b87a4d-5ab3-4c83-9676-e7e560641391n%40googlegroups.com.
