GHC.Prim does not export Constraint

This code from the effect-monad library worked in ghc-7.10, but fails with ghc-8.0.1-rc1:

{-# LANGUAGE TypeFamilies, ConstraintKinds, PolyKinds #-}

module Control.Effect.Cond where

import GHC.Prim

class Cond (m :: k -> * -> *) where
    type AltInv m (s :: k) (t :: k) :: Constraint

It seems one now needs to import Constraint from GHC.Exts.

This should be mentioned in the migration guide (https://ghc.haskell.org/trac/ghc/wiki/Migration/8.0), together with any other breaking changes there might be from the kind equalities patch (67465497).

Trac metadata

Trac field	Value
Version	8.0.1-rc1
Type	Bug
TypeOfFailure	OtherFailure
Priority	highest
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed milestone to %8.0.1

changed weight to 10

added Tbug Trac import labels

As I understand it, GHC.Exts is the One Official Place from where to import magic GHC gubbins, so I didn't worry too much about moving things around behind the scenes. I'll add a note to the migration guide.

There should not be other breakages from the kind equalities patch.

closed

Updated the wiki page.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

Thank you.

added Phighest label