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  • #16139

Closed
Open
Opened Jan 07, 2019 by Ashley Yakeley@AshleyYakeleyDeveloper

GHC confused about type synonym kind with QuantifiedConstraints

{-# LANGUAGE KindSignatures, RankNTypes, ConstraintKinds, QuantifiedConstraints #-}
module Bug where
import Data.Constraint

type E (c :: * -> Constraint) = forall (a :: *). Eq a => c a
Bug.hs:5:58: error:
    • Expected a type, but ‘c a’ has kind ‘Constraint’
    • In the type ‘forall (a :: *). Eq a => c a’
      In the type declaration for ‘E’
  |
5 | type E (c :: * -> Constraint) = forall (a :: *). Eq a => c a
  |                                                          ^^^

Note that GHC accepts the program when the Eq a constraint is removed.

Trac metadata
Trac field Value
Version 8.6.3
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
Test case
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Reference: ghc/ghc#16139