Type families regression
Here is a small program:
type family F a b
type instance F (Maybe a) b = b -> F a b
class C a where
go :: (forall a. Maybe a -> b -> a) -> a -> F a b
instance C a => C (Maybe a) where
go f a b = go f (f a b)
The current head complains:
Could not deduce (F a b ~ F a b) from the context (C a)
NB: `F' is a type function, and may not be injective
Expected type: b -> F a b
Actual type: F (Maybe a) b
- 12.3 accepts it.
Trac metadata
Trac field | Value |
---|---|
Version | 7.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |