+data Prototype = Prototype String [String]
+ deriving Show
+
+instance Read Prototype where
+ readPrec = lift $ do
+ name <- munch1 isAlpha
+ params <- between (char '(') (char ')') $
+ sepBy (munch1 isAlpha) skipSpaces
+ return (Prototype name params)
+
+data AST = Function Prototype Expr
+ | Extern Prototype
+ | TopLevelExpr Expr
+ deriving Show
+
+instance Read AST where
+ readPrec = parseFunction +++ parseExtern +++ parseTopLevel
+ where parseFunction = do
+ lift $ string "def" >> skipSpaces
+ Function <$> readPrec <*> readPrec
+ parseExtern = do
+ lift $ string "extern" >> skipSpaces
+ Extern <$> readPrec
+ parseTopLevel = TopLevelExpr <$> readPrec