Oddity with ConstraintKinds and TypeFamilies
See the attached program (not sure how to reduce it further - I don't know whether the relevant interaction is really with !TypeFamilies, Rank2Types, or what).
When compiled with -DWORKAROUND, it compiles, when without, it doesn't. The difference:
#ifndef WORKAROUND
ap :: (forall a. C e a => a -> r) -> e -> r
#else
ap :: c ~ C e => (forall a. c a => a -> r) -> e -> r
#endif(Where 'C e' is an associated type of 'e' of kind * -> Constraint.)
I sort of assumed that 'Some Type' and 'a ~ Some Type => a' would always be equivalent, but maybe I'm wrong. Feel free to mark as invalid if I am.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |