Another regression with type families
Program (compile with !ScopedTypeVariables):
type family H s a b
class D (G v) => C v where
type G v
type F v
foo :: v -> H (F v) (G v) v
class D s where
bar :: (forall t. Maybe t -> a) -> s -> H a s r -> r
call :: forall v. C v => F v -> v
call x = bar (\_ -> x)
(undefined :: G v)
(foo (undefined :: v))
bar' :: C v => (forall t. Maybe t -> F v) -> G v -> H (F v) (G v) v -> v
bar' = bar
The current head (even with today's typechecker patch) complains:
Could not deduce (H a (G v) v ~ H (F v) (G v) v)
from the context (C v)
But if I change bar
to bar'
in the rhs of foo
, it all works fine. 6.12.3 accepts both programs.
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 |