#4056: GHC panic with small TH code
---------------------------------+------------------------------------------
    Reporter:  verdelyi          |       Owner:                    
        Type:  bug               |      Status:  new               
    Priority:  normal            |   Component:  Template Haskell  
     Version:  6.12.2            |    Keywords:                    
          Os:  Unknown/Multiple  |    Testcase:                    
Architecture:  Unknown/Multiple  |     Failure:  Compile-time crash
---------------------------------+------------------------------------------
 [verde...@localhost CompilerGenerator-Haskell]$ cat BUG.hs
 {-# LANGUAGE TemplateHaskell, TypeFamilies, RankNTypes, FlexibleContexts
 #-}

 import Language.Haskell.TH

 astTest :: Q [Dec]
 astTest = [d|
     generateWalker :: forall t . [t] -> [t]
     generateWalker = id

     class (Num (From t), Num (To t)) => TransformationPhase t where
         type From t
         type To t
         type Downwards t
         type Upwards t

         executeTransformationPhase :: [t] -> [t]
         executeTransformationPhase = undefined
   |]
 [verde...@localhost CompilerGenerator-Haskell]$ ghci BUG.hs
 GHCi, version 6.12.2: http://www.haskell.org/ghc/  :? for help
 Loading package ghc-prim ... linking ... done.
 Loading package integer-gmp ... linking ... done.
 Loading package base ... linking ... done.
 Loading package ffi-1.0 ... linking ... done.
 [1 of 1] Compiling Main             ( BUG.hs, interpreted )
 ghc: panic! (the 'impossible' happened)
   (GHC version 6.12.2 for i386-unknown-linux):
         nameModule executeTransformationPhase{v agj}

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

 >

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4056>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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