module AST where
+import Data.Char
import Text.Read
import Text.ParserCombinators.ReadP hiding ((+++), choice)
-data BinOpType = Add | Sub | Mul
+data AST = Function String [String] Expr
+ | Eval Expr
deriving Show
data Expr = Num Float
| 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 = choice [ parseNum
+ , parseVar
+ , parseCall
, parseBinOp '+' Add
, parseBinOp '-' Sub
, parseBinOp '*' Mul
]
where parseNum = Num <$> readPrec
+ parseVar = Var <$> 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