Folks, I'm transforming ASTs as part of my compiler from one language into another. The source AST is a list of statements whereas the target AST is a "class definition". type Object a = State Obj a data Obj = Object { objSym :: Integer -- starting # for gensym , objVars :: M.Map String VarDecl , objProps :: M.Map String PropDecl , objMeths :: M.Map String MethodDecl } deriving (Show, Eq) I'm using a state monad and the transformations are supposed to update the state (object) as needed to add variables, methods, etc. class Morpher a b | a -> b where morph :: a -> Object b I have a lot of boilerplate code like this and wonder how I can scrape it. instance Morpher Type C.Type where morph TyInt = return C.TyInt morph TyFloat = return C.TyFloat morph TyStr = return C.TyStr morph TyBool = return C.TyBool morph TyColor = return C.TyColor morph TyStyle = return C.TyStyle morph (TyList ty) = liftM C.TyList (morph ty) morph (TyArray ty) = liftM C.TyArray (morph ty) morph (TySeries ty) = liftM C.TySeries (morph ty) morph (TyInput ty) = liftM C.TyProp (morph ty) morph (TyRef ty) = liftM C.TyRef (morph ty) morph TyUnit = return C.TyUnit morph TyPrintDest = return C.TyPrintDest Notice that I'm calling a constructor of the same name in a different module ... unless it's an exception. instance Morpher BackRef C.Expr where morph Now = C.Int 0 morph (BarsBack e) = morph e instance Morpher DataRef C.Expr where morph (DS x) = C.Int x How can I reduce the boilerplate here? Thanks, Joel -- http://wagerlabs.com/