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 > <javascript:>> 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 <javascript:>. > > For more options, visit https://groups.google.com/d/optout. >
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