Unidirectional pattern signatures do not need to be invariant w.r.t. higher-rank polymorphism
Best explained by example:
data T = MkT (forall a. a -> a)
pattern PT :: (Int -> Int) -> T
pattern PT x <- MkT x
This looks perfectly reasonable to me. And the hand-written matcher is also accepted. Note that a similar bidirectional pattern synonym should indeed be rejected.
Trac metadata
Trac field | Value |
---|---|
Version | 8.2.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |