Given this program:
{-# OPTIONS -fglasgow-exts #-}
module Bug1 where
import Control.Monad.State
newtype T a = T (StateT Int IO a) deriving (MonadState)
GHC 5.04.2 chokes:
ghc-5.04.2: chasing modules from: Bug1
Compiling Bug1 ( Bug1.hs, ./Bug1.o )
ghc-5.04.2: panic! (the `impossible' happened, GHC version 5.04.2):
basicTypes/VarEnv.lhs:173: Non-exhaustive patterns in case
Of course, the program is in error. (It should derive `MonadState Int`.)
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