[verdelyi@localhost CompilerGenerator-Haskell]$ cat BUG.hs {-# LANGUAGE TemplateHaskell, TypeFamilies, RankNTypes, FlexibleContexts #-}import Language.Haskell.THastTest :: 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 |][verdelyi@localhost CompilerGenerator-Haskell]$ ghci BUG.hs GHCi, version 6.12.2: http://www.haskell.org/ghc/ :? for helpLoading 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>