module AST where
+import Data.Char
import Text.Read
import Text.ParserCombinators.ReadP hiding ((+++), choice)
data Expr = Num Float
+ | Var String
| BinOp BinOp Expr Expr
deriving Show
deriving Show
instance Read Expr where
- readPrec = choice [ parseNum
+ readPrec = parens $ choice [ parseNum
+ , parseVar
, parseBinOp "<" 10 (Cmp LT)
, parseBinOp "+" 20 Add
, parseBinOp "-" 20 Sub
, parseBinOp "*" 40 Mul
]
where parseNum = Num <$> readPrec
- -- use 'prec 1' and 'step' so that parsing 'a'
- -- can only go one step deep, to prevent ininfite
- -- recursion
+ parseVar = Var <$> lift (munch1 isAlpha)
parseBinOp s prc op = prec prc $ do
a <- step readPrec
lift $ do
b <- readPrec
return (BinOp op a b)
+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