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Parse.hs
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Parse.hs
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module Parse where
import Text.ParserCombinators.Parsec hiding (spaces)
import Monad
data LispVal = Atom String
| List [LispVal]
| DottedList [LispVal] LispVal
| Number Integer
| String String
| Bool Bool
instance Show LispVal where
show = showVal
symbol :: Parser Char
symbol = oneOf "!$%&|*+-/:<=?>@^_~#"
spaces :: Parser()
spaces = skipMany1 space
parseString :: Parser LispVal
parseString = do
char '"'
x <- many (noneOf "\"")
char '"'
return $ String x
parseAtom :: Parser LispVal
parseAtom = do
first <- letter <|> symbol
rest <- many (letter <|> digit <|> symbol)
let atom = first:rest
return $ case atom of
"#t" -> Bool True
"#f" -> Bool False
otherwise -> Atom atom
parseNumber :: Parser LispVal
parseNumber = liftM (Number . read) $ many1 digit
parseList :: Parser LispVal
parseList = liftM List $ sepBy parseExpr spaces
parseDottedList :: Parser LispVal
parseDottedList = do
head <- endBy parseExpr spaces
tail <- char '.' >> spaces >> parseExpr
return $ DottedList head tail
parseQuoted :: Parser LispVal
parseQuoted = do
char '\''
x <- parseExpr
return $ List [Atom "quote", x]
parseExpr :: Parser LispVal
parseExpr = parseAtom
<|> parseString
<|> parseNumber
<|> parseQuoted
<|> do char '('
x <- (try parseList) <|> parseDottedList
char ')'
return x
------------- Book ShowVal ---------------------
showVal :: LispVal -> String
showVal (String contents) = "\"" ++ contents ++ "\""
showVal (Atom name) = name
showVal (Number contents) = show contents
showVal (Bool True) = "#t"
showVal (Bool False) = "#f"
showVal (List contents) = "(" ++ unwordsList contents ++ ")"
showVal (DottedList head tail) = "(" ++ unwordsList head ++ " . " ++ showVal tail ++ ")"
unwordsList :: [LispVal] -> String
unwordsList = unwords . map showVal
------------- My ShowVal ------------------------
{-
showVal :: LispVal -> String
showVal (Atom str) = "atom " ++ str
showVal (List xs) = "( " ++ (showListVal xs) ++ " )"
showVal (DottedList ls vl) = showListVal ls ++ " . " ++ (showVal vl)
showVal (Number int) = show int
showVal (String s) = "string " ++ s
showVal (Bool b) = show b
showListVal :: [LispVal] -> String
showListVal [] = ""
showListVal [x] = showVal x
showListVal (x:xs) = (showVal x) ++ ',' : ' ' : (showListVal xs)
-}