Bug.hs

module Bug where

import Control.Monad
import Control.Monad.State (gets)
import Control.Monad.Trans.Class (lift)

foo = lift lift gets

{-
$ ghc bug.hs 
[1 of 1] Compiling Bug              ( bug.hs, bug.o )

bug.hs:7:7:
    Couldn't match kind `* -> *' with `*'
    Expected type: ((s0 -> a1) -> m1 a1) -> t0 m0 a0
      Actual type: ((s0 -> a1) -> m1 a1) -> t0 m0 a0
    Kind incompatibility when matching types:
      (s_j -> a_k) -> m_l a_k :: * -> *
      (s0 -> a1) -> m1 a1 :: *
    The function `lift'ghc: panic! (the 'impossible' happened)
  (GHC version 7.6.3 for x86_64-unknown-linux):
	kindFunResult ghc-prim:GHC.Prim.*{(w) tc 34d}

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
-}