+data BinOpType = Add | Sub | Mul
+ deriving Show
+
+instance Read AST where
+ readPrec = parseFunction +++ (Eval <$> readPrec)
+ where parseFunction = lift $ do
+ skipSpaces
+ string "def"
+ skipSpaces
+ name <- munch1 isAlpha
+ params <- between (char '(') (char ')') $
+ sepBy (munch1 isAlpha) skipSpaces
+ skipSpaces
+ body <- readS_to_P reads
+ return (Function name params body)