5 import Text.ParserCombinators.ReadP hiding ((+++), (<++), choice)
9 | BinOp BinOp Expr Expr
12 | For String Expr Expr (Maybe Expr) Expr
15 data BinOp = Add | Sub | Mul | Cmp Ordering
18 instance Read Expr where
19 readPrec = parens $ choice [ parseNum
24 , parseBinOp "<" 10 (Cmp LT)
25 , parseBinOp ">" 10 (Cmp GT)
26 , parseBinOp "==" 10 (Cmp EQ)
27 , parseBinOp "+" 20 Add
28 , parseBinOp "-" 20 Sub
29 , parseBinOp "*" 40 Mul
31 where parseNum = Num <$> readPrec
32 parseVar = Var <$> lift (munch1 isAlpha)
33 parseBinOp s prc op = prec prc $ do
39 func <- lift (munch1 isAlpha)
40 params <- lift $ between (char '(') (char ')') $
41 sepBy (readS_to_P reads)
42 (skipSpaces >> char ',' >> skipSpaces)
43 return (Call func params)
47 spaced $ string "then"
49 spaced $ string "else"
51 return (If cond thenE elseE)
54 identifier <- lift (munch1 isAlpha)
59 stp <- (spaced (char ',') >> Just <$> step readPrec)
63 return (For identifier start cond stp body)
64 spaced f = lift $ skipSpaces >> f >> skipSpaces
66 data Prototype = Prototype String [String]
69 instance Read Prototype where
71 name <- munch1 isAlpha
72 params <- between (char '(') (char ')') $
73 sepBy (munch1 isAlpha) skipSpaces
74 return (Prototype name params)
76 data AST = Function Prototype Expr
81 instance Read AST where
82 readPrec = parseFunction +++ parseExtern +++ parseTopLevel
83 where parseFunction = do
84 lift $ string "def" >> skipSpaces
85 Function <$> readPrec <*> readPrec
87 lift $ string "extern" >> skipSpaces
89 parseTopLevel = TopLevelExpr <$> readPrec