Folks, I'm trying to save time when typing in my ASTs so I thought I would create a Plus class like this (I do hide the one from Prelude) class PlusClass a b c | a b -> c where (+) :: a -> b -> c {- instance (Integral a, Integral b) => PlusClass a b Expr where a + b = NumExpr (NumOp Plus (Int (fromIntegral a)) (Int (fromIntegral b))) instance Integral a => PlusClass a Double Expr where a + b = NumExpr (NumOp Plus (Int (fromIntegral a)) (Double b)) -} instance PlusClass Integer Integer Expr where a + b = NumExpr (NumOp Plus (Int a) (Int b)) instance PlusClass Double Integer Expr where a + b = NumExpr (NumOp Plus (Double a) (Int b)) instance PlusClass NumExpr NumExpr Expr where a + b = NumExpr (NumOp Plus a b) instance PlusClass Integer NumExpr Expr where a + b = NumExpr (NumOp Plus (Int a) b) instance PlusClass NumExpr Integer Expr where a + b = NumExpr (NumOp Plus a (Int b)) instance PlusClass String String Expr where a + b = StrExpr (StrOp StrPlus (Str a) (Str b)) NumExpr and StrExpr return Expr whereas Int, Double return NumExpr and Str returns StrExpr. This is all so that I could type in input2 = [ InputDecs [ inp "emaLength" TyNumber (20 + 40) ] ] Still, I get the following error Easy/Test/ParserAST.hs:76:44: No instance for (PlusClass t t1 Expr) arising from use of `+' at Easy/Test/ParserAST.hs:76:44-50 Possible fix: add an instance declaration for (PlusClass t t1 Expr) In the third argument of `inp', namely `(20 + 40)' In the expression: inp "emaLength" TyNumber (20 + 40) In the first argument of `InputDecs', namely `[inp "emaLength" TyNumber (20 + 40)]' and get an overlapped instances error if I uncomment the top portion. Any suggestions on how to resolve this? Thanks, Joel -- http://wagerlabs.com/