module AST where
+import Data.Char
import Text.Read
-import Text.ParserCombinators.ReadP hiding ((+++), choice)
+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
+ | For String Expr Expr (Maybe Expr) Expr
deriving Show
data BinOp = Add | Sub | Mul | Cmp Ordering
deriving Show
instance Read Expr where
- readPrec = choice [ parseNum
+ readPrec = parens $ choice [ parseNum
, parseVar
+ , parseCall
+ , parseIf
+ , parseFor
, parseBinOp "<" 10 (Cmp LT)
+ , parseBinOp ">" 10 (Cmp GT)
+ , parseBinOp "==" 10 (Cmp EQ)
, parseBinOp "+" 20 Add
, parseBinOp "-" 20 Sub
, parseBinOp "*" 40 Mul
]
where parseNum = Num <$> readPrec
parseVar = Var <$> lift (munch1 isAlpha)
- -- use 'prec 1' and 'step' so that parsing 'a'
- -- can only go one step deep, to prevent ininfite
- -- recursion
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
+ func <- lift (munch1 isAlpha)
+ params <- lift $ between (char '(') (char ')') $
+ 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)
+ parseFor = do
+ spaced $ string "for"
+ identifier <- lift (munch1 isAlpha)
+ spaced $ char '='
+ start <- readPrec
+ spaced $ char ','
+ cond <- readPrec
+ stp <- (spaced (char ',') >> Just <$> step readPrec)
+ <++ pure Nothing
+ spaced $ string "in"
+ body <- readPrec
+ return (For identifier start cond stp body)
+ spaced f = lift $ skipSpaces >> f >> skipSpaces
+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