GHC allows you to quantify variables over TYPE 'Unlifted (a.k.a, #)

This should be disallowed, so sayeth goldfire:

$ inplace/bin/ghc-stage2 --interactive
GHCi, version 8.1.20160109: http://www.haskell.org/ghc/  :? for help
λ> :set -XKindSignatures 
λ> import GHC.Types
λ> data Wat (a :: TYPE 'Unlifted) = Wat a
λ> :i Wat
data Wat (a :: #) = Wat a       -- Defined at <interactive>:3:1
λ> :set -XMagicHash 
λ> :t Wat 1#
Wat 1# :: Wat GHC.Prim.Int#
λ> :t Wat 'a'#
Wat 'a'# :: Wat GHC.Prim.Char#

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	goldfire
Operating system
Architecture