Use injective type families (decomposition) when dealing with givens
Consider this code:
type family Id a = r | r -> a
id :: (Id a ~ Id b) => a -> b
id x = xGHC currently rejects it because it does not use type family injectivity information when dealing with the given constraints. Implementing this requires changing Core.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.10.2 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | #6018 (closed) |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |