Yes, this is because the contract enforces parametericity, which doesn't allow `index-of` to work the way you'd want.
Instantiating things doesn't help because the contract is based on the `require/typed`, not on the use site. Here's a few suggestions: 1. Submit a pull-request to TR to add `index-of` 2. Import `index-of` at a concrete type 3. Use `unsafe-require/typed` 4. Use the third argument to `index-of?` Sam On Sun, Dec 15, 2019 at 9:28 PM 'John Clements' via Racket Users <racket-users@googlegroups.com> wrote: > > It looks like my quick attempt at importing index-of into TR is running into > a problem. Here’s the program I ran: > > #lang typed/racket > > (require/typed racket/list > [index-of (All (T) ((Listof T) T -> (U False Natural)))]) > > (index-of '(n s e w) 'n) ;; returns... #f? > > In typed/racket/no-check this returns 0, and also in racket (mutatis > mutandis). > > I thought this might be some kind of parametricity issue, but even when I > instantiate index-of at Symbol which should pretty much clear the way for > arbitrary equality checking, I still get False. > > Am I missing something obvious? Maybe I shouldn’t be running from the > November 14 git head any more? > > Welcome to DrRacket, version 7.5.0.7--2019-11-14(-/f) [3m]. > > John > > > > -- > 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/ef401a3d-9c41-44f9-ba61-93c09065755e%40mtasv.net. -- 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/CAK%3DHD%2BaFwAPxwuf67_NxeqCeZQMfac%2BL8Vqf0fEbFDGxLPgmgg%40mail.gmail.com.
