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
> --
> 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.
> To view this discussion on the web visit
https://groups.google.com/d/msgid/racket-users/ef401a3d-9c41-44f9-ba61-93c09065755e%40mtasv.net.