completed non exercises part

time for exercises

simple_parser.hs

@@ -1,3 +1,4 @@
+import Control.Monad
 import System.Environment
 import Text.ParserCombinators.Parsec hiding (spaces)
 
@@ -7,8 +8,37 @@ symbol = oneOf "!#$%&|*+-/:<=>?@^_~"
 spaces :: Parser ()
 spaces = skipMany1 space
 
+data LispVal = Atom String
+    | List [LispVal]
+    | DottedList [LispVal] LispVal
+    | Number Integer
+    | String String
+    | Bool Bool
+
+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
+                   _ -> Atom atom
+
+parseNumber :: Parser LispVal
+parseNumber = liftM (Number . read) $ many1 digit
+
+parseExpr :: Parser LispVal
+parseExpr = parseAtom <|> parseString <|> parseNumber
+
 readExpr :: String -> String
-readExpr input = case parse (spaces >> symbol) "lisp" input of
+readExpr input = case parse parseExpr "lisp" input of
     Left err -> "No match: " ++ show err
     Right val -> "Found value"