Yes, a cast to a List type checks all the elements of the list. There's no way to tell if every element of list is a string in less than O(N) time -- that information just isn't available anywhere.
Sam On Thu, Feb 28, 2019 at 3:52 PM Brian Craft <craft.br...@gmail.com> wrote: > > Really? A cast is also O(N)? > > On Thursday, February 28, 2019 at 11:11:01 AM UTC-8, Sam Tobin-Hochstadt > wrote: >> >> Any of these solutions need a O(N) traversal of the data. That's >> because we need to do a full traversal to be sure we got an actual >> (Listof String) from read-json -- there's no way around it. >> >> Sam >> >> On Thu, Feb 28, 2019 at 2:04 PM Brian Craft <craft...@gmail.com> wrote: >> > >> > I would think there'd be a large performance issue, as well, due to >> > needing an O(N) walk of the data. I'm having type checker issues with >> > (time), so haven't tested it, but maybe (cast) will get me past those. >> > >> > Thanks! >> > >> > On Monday, February 25, 2019 at 4:26:52 PM UTC-8, Philip McGrath wrote: >> >> >> >> An alternative to figuring out how to satisfy the type checker is to use >> >> `cast`, e.g.: >> >> #lang typed/racket >> >> (require typed/json) >> >> (string-join >> >> (cast >> >> (string->jsexpr >> >> "[\"The\",\"quick\",\"brown\",\"fox\",\"...\"]") >> >> (Listof String))) >> >> >> >> Obviously this has pros and cons, the main pro being that it runs. The >> >> biggest con, in my view, is that you effectively are dropping into >> >> untyped world. If you figure out how to satisfy the type checker, you get >> >> assurance that your code is well-typed, which is presumably what you want >> >> if your using Typed Racket in the first place. Using `cast` means that >> >> you are responsible for making sure that expression has the type you say >> >> it does, without help from Typed Racket, or you will get a runtime error. >> >> For example, I often forget that `read-json` might return `eof` rather >> >> than a `JSExpr`. Also, `cast` uses the contract machinery, which can >> >> carry performance costs. >> >> >> >> But the fact that it runs is not a small benefit, especially if it lets >> >> you fill in other parts of your program and come back to remove the >> >> `cast` later. It also lets you take advantage of Typed Racket to generate >> >> any complicated runtime checks. >> >> >> >> -Philip >> >> >> >> >> >> On Mon, Feb 25, 2019 at 6:49 PM <jackh...@gmail.com> wrote: >> >>> >> >>> A JSExpr is one of a couple of things: >> >>> >> >>> - A list >> >>> - A hash with symbol keys >> >>> - A number >> >>> - A string >> >>> - A boolean >> >>> - Null >> >>> >> >>> The (andmap string?) approach implicitly assumes you're giving it a >> >>> list. But it might be something else instead, so you want this: (and >> >>> (list? js) (andmap string? js)) >> >>> >> >>> On Monday, February 25, 2019 at 3:44:38 PM UTC-8, Brian Craft wrote: >> >>>> >> >>>> So, that also gives me a type error: >> >>>> >> >>>> Type Checker: Polymorphic function `andmap' could not be applied to >> >>>> arguments: >> >>>> Domains: (-> a b ... b c) (Listof a) (Listof b) ... b >> >>>> (-> a c : d) (Listof a) >> >>>> Arguments: (-> Any Boolean : String) (U EOF JSExpr) >> >>>> >> >>>> in: (andmap string? s) >> >>>> >> >>>> >> >>>> On Monday, February 25, 2019 at 3:22:12 PM UTC-8, Sam Tobin-Hochstadt >> >>>> wrote: >> >>>>> >> >>>>> I think (andmap string? ...) is probably the easiest way to check that. >> >>>>> >> >>>>> Sam >> >>>>> >> >>>>> On Mon, Feb 25, 2019, 6:20 PM Brian Craft <craft...@gmail.com> wrote: >> >>>>>> >> >>>>>> In typed racket, parsing a string list gives me a JSExpr, which is a >> >>>>>> union. I need to pass it to functions that operate on string lists, >> >>>>>> but can't figure out how to please the type checker. Maybe with >> >>>>>> occurrence typing? But I don't know how to assert "this is a list of >> >>>>>> strings". >> >>>>>> >> >>>>>> -- >> >>>>>> 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...@googlegroups.com. >> >>>>>> For more options, visit https://groups.google.com/d/optout. >> >>> >> >>> -- >> >>> 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...@googlegroups.com. >> >>> For more options, visit https://groups.google.com/d/optout. >> > >> > -- >> > 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...@googlegroups.com. >> > For more options, visit https://groups.google.com/d/optout. > > -- > 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. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. 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