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
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