+instance Read Program where
+ readPrec = fmap Program $ lift $ do
+ asts <- sepBy1 (readS_to_P reads) $ do
+ skipSpaces
+ char ';'
+ skipSpaces
+ optional $ char ';'
+ skipSpaces
+ return asts
+
+data AST = Function String [String] Expr
+ | Extern String [String]
+ | Eval Expr
+ deriving Show
+data Expr = Num Double
+ | BinOp BinOpType Expr Expr
+ | Var String
+ | Call String [Expr]
+ | If Expr Expr Expr
+ | For String Expr Expr (Maybe Expr) Expr
+ deriving Show
+data BinOpType = Add | Sub | Mul | Cmp Ordering
+ deriving Show
+
+instance Read AST where
+ readPrec = parseFunction +++ parseExtern +++ (Eval <$> readPrec)
+ where parseFunction = do
+ lift $ string "def" >> skipSpaces
+ (name, params) <- parsePrototype
+ lift skipSpaces
+ Function name params <$> readPrec
+ parseExtern = do
+ lift $ string "extern" >> skipSpaces
+ uncurry Extern <$> parsePrototype
+ parsePrototype = lift $ do
+ name <- munch1 isAlpha
+ params <- between (char '(') (char ')') $
+ sepBy (munch1 isAlpha) skipSpaces
+ return (name, params)
+