import Text.Read
import Text.ParserCombinators.ReadP hiding ((+++), choice)
+newtype Program = Program [AST]
+ deriving Show
+
+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 Float
+data Expr = Num Double
| BinOp BinOpType Expr Expr
| Var String
| Call String [Expr]
+ | If Expr Expr Expr
deriving Show
-data BinOpType = Add | Sub | Mul
+data BinOpType = Add | Sub | Mul | Cmp Ordering
deriving Show
instance Read AST where
- readPrec = parseFunction +++ (Eval <$> readPrec)
- where parseFunction = lift $ do
- skipSpaces
- string "def"
- skipSpaces
+ 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
- skipSpaces
- body <- between (char '{') (char '}') $
- readS_to_P reads
- skipSpaces
- return (Function name params body)
+ return (name, params)
instance Read Expr where
- readPrec = choice [ parseNum
+ readPrec = choice [ parseParens
+ , parseNum
, parseVar
, parseCall
- , parseBinOp '+' Add
- , parseBinOp '-' Sub
- , parseBinOp '*' Mul
+ , parseIf
+ , parseBinOp "+" Add
+ , parseBinOp "-" Sub
+ , parseBinOp "*" Mul
+ , parseBinOp ">" (Cmp GT)
+ , parseBinOp "<" (Cmp LT)
+ , parseBinOp "==" (Cmp EQ)
]
- where parseNum = Num <$> readPrec
+ where parseParens = step $ lift $
+ between (char '(') (char ')') (readS_to_P reads)
+ parseNum = Num <$> readPrec
parseVar = Var <$> lift (munch1 isAlpha)
parseCall = do
func <- lift (munch1 isAlpha)
sepBy (readS_to_P reads)
(skipSpaces >> char ',' >> skipSpaces)
return (Call func params)
- parseBinOp c typ = step $ do
- a <- prec 11 readPrec
+ parseBinOp s typ = step $ do
+ a <- prec 11 readPrec -- set recursion limit of 11
+ lift $ do
+ skipSpaces
+ string s
+ skipSpaces
+ BinOp typ a <$> readPrec
+ parseIf = do
+ lift $ do
+ string "if"
+ skipSpaces
+ cond <- step readPrec
+ lift $ do
+ skipSpaces
+ string "then"
+ skipSpaces
+ thenE <- step readPrec
lift $ do
skipSpaces
- char c
+ string "else"
skipSpaces
- b <- readPrec
- return (BinOp typ a b)
+ elseE <- step readPrec
+ return (If cond thenE elseE)