import Text.Read
import Text.ParserCombinators.ReadP hiding ((+++), choice)
-data Expr = Num Float
+data Expr = Num Double
| Var String
| BinOp BinOp Expr Expr
| Call String [Expr]
+ | If Expr Expr Expr
deriving Show
data BinOp = Add | Sub | Mul | Cmp Ordering
readPrec = parens $ choice [ parseNum
, parseVar
, parseCall
+ , parseIf
, parseBinOp "<" 10 (Cmp LT)
+ , parseBinOp ">" 10 (Cmp GT)
+ , parseBinOp "==" 10 (Cmp EQ)
, parseBinOp "+" 20 Add
, parseBinOp "-" 20 Sub
, parseBinOp "*" 40 Mul
parseVar = Var <$> lift (munch1 isAlpha)
parseBinOp s prc op = prec prc $ do
a <- step readPrec
- lift $ do
- skipSpaces
- string s
- skipSpaces
+ spaced $ string s
b <- readPrec
return (BinOp op a b)
parseCall = do
sepBy (readS_to_P reads)
(skipSpaces >> char ',' >> skipSpaces)
return (Call func params)
+ parseIf = do
+ spaced $ string "if"
+ cond <- readPrec
+ spaced $ string "then"
+ thenE <- readPrec
+ spaced $ string "else"
+ elseE <- readPrec
+ return (If cond thenE elseE)
+ spaced f = lift $ skipSpaces >> f >> skipSpaces
data Prototype = Prototype String [String]
deriving Show