Tuple constraints not properly kinded
Consider this:
{-# LANGUAGE DataKinds, ConstraintKinds, KindSignatures #-}
import GHC.Exts ( Constraint )
type UnitType = (() :: *)
type UnitConstraint = (() :: Constraint)
type PairType = ((,) :: * -> * -> *)
So far, so good. But, adding the following causes an error:
type PairConstraint = ((,) :: Constraint -> Constraint -> Constraint)
The error is
The signature specified kind `Constraint
-> Constraint -> Constraint',
but `(,)' has kind `* -> * -> *'
In general, you can't use the prefix form of (,)
in a constraint, to my surprise. It's not entirely clear what is the "correct" behavior here, but this all seems a little fishy as currently implemented.
This was all tested on 7.7.20121130.
Trac metadata
Trac field | Value |
---|---|
Version | 7.7 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |