5 import Text.ParserCombinators.ReadP hiding ((+++), choice)
9 | BinOp BinOp Expr Expr
13 data BinOp = Add | Sub | Mul | Cmp Ordering
16 instance Read Expr where
17 readPrec = parens $ choice [ parseNum
20 , parseBinOp "<" 10 (Cmp LT)
21 , parseBinOp "+" 20 Add
22 , parseBinOp "-" 20 Sub
23 , parseBinOp "*" 40 Mul
25 where parseNum = Num <$> readPrec
26 parseVar = Var <$> lift (munch1 isAlpha)
27 parseBinOp s prc op = prec prc $ do
36 func <- lift (munch1 isAlpha)
37 params <- lift $ between (char '(') (char ')') $
38 sepBy (readS_to_P reads)
39 (skipSpaces >> char ',' >> skipSpaces)
40 return (Call func params)
42 data Prototype = Prototype String [String]
45 instance Read Prototype where
47 name <- munch1 isAlpha
48 params <- between (char '(') (char ')') $
49 sepBy (munch1 isAlpha) skipSpaces
50 return (Prototype name params)
52 data AST = Function Prototype Expr
57 instance Read AST where
58 readPrec = parseFunction +++ parseExtern +++ parseTopLevel
59 where parseFunction = do
60 lift $ string "def" >> skipSpaces
61 Function <$> readPrec <*> readPrec
63 lift $ string "extern" >> skipSpaces
65 parseTopLevel = TopLevelExpr <$> readPrec