[GHC] #1494: panic! (the 'impossible' happened)

[GHC]

#1494: panic! (the 'impossible' happened)
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    Reporter:  iampure at gmail.com  |        Owner:         
        Type:  bug                |       Status:  new    
    Priority:  highest            |    Milestone:         
   Component:  GHCi               |      Version:  6.7    
    Severity:  blocker            |   Resolution:         
    Keywords:                     |   Difficulty:  Unknown
          Os:  Unknown            |     Testcase:         
Architecture:  Unknown            |  
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Comment (by simonpj):

 I've boiled it down more:
 {{{
 module Foo where

 import Control.Monad.State

 newtype L m r = L (StateT Int m r)

 instance Monad m => Monad (L m)

 zork :: (Monad m) => a -> L m ()
 zork = undefined

 mumble e = do { modify id; zork e }
 }}}
 Compiling this with `-dcore-lint` shows the error.  More anon.

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1494>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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