On Tue, Nov 1, 2016 at 2:52 PM, Robby Findler <ro...@eecs.northwestern.edu> wrote:
> > > On Tuesday, November 1, 2016, David Storrs <david.sto...@gmail.com> wrote: > >> >> >> On Tue, Nov 1, 2016 at 12:58 PM, Robby Findler < >> ro...@eecs.northwestern.edu> wrote: >> >>> I wish I could see how to make a better error message for this input, >>> but I'm not seeing it. Do you? >>> >>> Robby >>> >>> >> With this function: >> >> (define/contract (register-functions . func-list) >> (->* () #:rest (listof procedure?) () any) >> >> I got this message: >> >> lib/test.rkt:56:5: ->*: expected the end of the contract >> at: (any) >> in: (->* () #:rest (listof procedure?) () any) >> >> >> I can see a couple of possible alternatives: >> >> 1) Call it a syntax error. That tells me that I've typed something >> wrong, as opposed to there being something I don't know about the semantics >> of contracts. >> > > It is a syntax error. > Absolutely, but that's not what the message says. :> > These might or might not still be errors, depending on how you look at it: >> >> (->* #:rest ... () result) >> (->* () #:rest ... result) >> >> If it's an error, the message I would suggest is: "Invalid contract. >> ->* requires both mandatory and optional argument lists, even if they are >> null." >> > > The optional argument list is optional actually. This is the root of the > problem: it thinks that the () was your range contract and then gets > confused that there is still more coming. > Maybe it shouldn't be optional, then? I'm not sure that saving two characters is worth the confusion that results from getting it wrong. I realize that making it optional without warning would break a lot of old code...maybe skipping the optional argument could be deprecated and eventually it could be rendered mandatory in a future release? > > > >> I think this works -- only one thing can follow the #:rest keyword, >> right? If so, it shouldn't be ambiguous what is referring to what. >> >> > I could say "only the rest argument contract and the result contract can > follow #:rest". Would that wording have helped? > Yep, that would have been perfect. > > Robby > > >> Dave >> >> On Tue, Nov 1, 2016 at 11:50 AM, David Storrs <david.sto...@gmail.com> >>> wrote: >>> > Aha. It's always the simple things that get you. Thanks, Alexis. >>> > >>> > On Tue, Nov 1, 2016 at 12:30 PM, Alexis King <lexi.lam...@gmail.com> >>> wrote: >>> >> >>> >> You have the order wrong for ->*. The #:rest option should come >>> >> after the positional argument contracts, just before the return >>> >> contract. Since this function has no positional optional arguments, >>> >> you can either omit the optional positional argument contracts >>> >> entirely: >>> >> >>> >> (->* () #:rest (listof procedure?) any) >>> >> >>> >> …or you can include it, before #:rest: >>> >> >>> >> (->* () () #:rest (listof procedure?) any) >>> >> >>> >> > On Nov 1, 2016, at 9:18 AM, David Storrs <david.sto...@gmail.com> >>> wrote: >>> >> > >>> >> > What would the correct contract for this function be? >>> >> > >>> >> > (define/contract (register-functions . func-list) >>> >> > (->* () #:rest (listof procedure?) () any) ;; this is wrong >>> >> > >>> >> > (for ((f func-list)) ...do something...)) >>> >> > >>> >> > >>> >> > I've read through the docs below and it doesn't make clear how to >>> do it. >>> >> > >>> >> > https://docs.racket-lang.org/guide/contracts-general-functions.html >>> >> > https://docs.racket-lang.org/reference/function-contracts.html >>> >> >>> >> -- >>> >> 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. >>> > 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. >> 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. > 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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