module AST where
+import Data.Char
import Text.Read
-import Text.ParserCombinators.ReadP hiding ((+++))
+import Text.ParserCombinators.ReadP hiding ((+++), choice)
+newtype Program = Program [AST]
+ deriving Show
+
+instance Read Program where
+ readPrec = fmap Program $ lift $ sepBy1 (readS_to_P reads) $ do
+ skipSpaces
+ char ';'
+ skipSpaces
+
+data AST = Function String [String] Expr
+ | Eval Expr
+ deriving Show
data Expr = Num Float
- | Add Expr Expr
+ | BinOp BinOpType Expr Expr
+ | Var String
+ | Call String [Expr]
+ | If Expr Expr Expr
+ deriving Show
+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
+ name <- munch1 isAlpha
+ params <- between (char '(') (char ')') $
+ sepBy (munch1 isAlpha) skipSpaces
+ skipSpaces
+ body <- readS_to_P reads
+ return (Function name params body)
+
instance Read Expr where
- readPrec = parseNum +++ parseAdd
+ readPrec = choice [ parseNum
+ , parseVar
+ , parseCall
+ , parseIf
+ , parseBinOp "+" Add
+ , parseBinOp "-" Sub
+ , parseBinOp "*" Mul
+ , parseBinOp ">" (Cmp GT)
+ , parseBinOp "<" (Cmp LT)
+ , parseBinOp "==" (Cmp EQ)
+ ]
where parseNum = Num <$> readPrec
- parseAdd = step $ do
+ parseVar = Var <$> lift (munch1 isAlpha)
+ parseCall = do
+ func <- lift (munch1 isAlpha)
+ params <- lift $ between (char '(') (char ')') $
+ sepBy (readS_to_P reads)
+ (skipSpaces >> char ',' >> skipSpaces)
+ return (Call func params)
+ parseBinOp s typ = step $ do
a <- prec 11 readPrec
lift $ do
skipSpaces
- char '+'
+ string s
skipSpaces
b <- readPrec
- return (Add a b)
+ return (BinOp typ a b)
+ parseIf = do
+ lift $ do
+ string "if"
+ skipSpaces
+ cond <- step readPrec
+ lift $ do
+ skipSpaces
+ string "then"
+ skipSpaces
+ thenE <- step readPrec
+ lift $ do
+ skipSpaces
+ string "else"
+ skipSpaces
+ elseE <- step readPrec
+ return (If cond thenE elseE)