I'm looking for suggestions on how to create invariants for the following AST transformation code. Any suggestions are appreciated! I asked this question before and Lennart suggested abstract interpretation as a solution. This would require interpreters for both ASTs to determine that the result they achieve is the same. I don't fancy writing a C# interpreter, though, so I'm looking for an easier way out. Thanks, Joel [1] http://tinyurl.com/368whq --- instance SharpTransform C.Type Type where toSharp C.TyInt = return TyInt toSharp C.TyFloat = return TyFloat toSharp C.TyStr = return TyStr toSharp C.TyBool = return TyBool toSharp (C.TyArray x) = liftM2 TyArray (toSharp x) (return []) toSharp (C.TySeries C.TyFloat) = return $ TyCustom "DataSeries" toSharp (C.TySeries x) = error $ "Unsupported series type: " ++ show x toSharp (C.TyProp x) = toSharp x toSharp C.TyUnit = return TyVoid instance SharpTransform C.VarIdent VarIdent where toSharp (C.VarIdent x) = return $ VarIdent x instance SharpTransform (Maybe C.Expr) (Maybe Expr) where toSharp Nothing = return Nothing toSharp (Just e) = liftM Just (toSharp e) instance SharpTransform C.Subscript [Expr] where toSharp xs = mapM toSharp xs instance SharpTransform C.BarsAgo Expr where toSharp C.Now = return $ Int 0 toSharp (C.BarsAgo e) = toSharp e -- http://wagerlabs.com/