module AST where
+import Data.Char
import Text.Read
-import Text.ParserCombinators.ReadP hiding ((+++))
+import Text.ParserCombinators.ReadP hiding ((+++), choice)
+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]
+ deriving Show
+data BinOpType = Add | Sub | Mul
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 <- between (char '{') (char '}') $
+ readS_to_P reads
+ skipSpaces
+ return (Function name params body)
+
instance Read Expr where
- readPrec = parseNum +++ parseAdd
+ readPrec = choice [ parseNum
+ , parseVar
+ , parseCall
+ , parseBinOp '+' Add
+ , parseBinOp '-' Sub
+ , parseBinOp '*' Mul
+ ]
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 c typ = step $ do
a <- prec 11 readPrec
lift $ do
skipSpaces
- char '+'
+ char c
skipSpaces
b <- readPrec
- return (Add a b)
+ return (BinOp typ a b)