Added lambda syntax on the language

src/Lexer.hs

@@ -12,7 +12,7 @@ parseTokens = do
     return tokns
 
 anyLispToken :: GenParser Char st Token
-anyLispToken = leftParenT <|> rightParenT <|> apostropheT <|> symbolT <|> intT
+anyLispToken = leftParenT <|> rightParenT <|> apostropheT <|> backslashT <|> symbolT <|> intT
 
 ------------------------------------------------------------
 
@@ -30,7 +30,10 @@ apostropheT = char '\'' >> return ApostropheT
 rightParenT :: GenParser Char st Token
 rightParenT = char ')' >> return RightParenT
 
+backslashT :: GenParser Char st Token
+backslashT = char '\\' >> return BackslashT
+
 symbolT :: GenParser Char st Token
 symbolT = do
-    var <- map toLower <$> many1 (letter <|> oneOf "+-*/\\!|@#$~%&/=<>")
+    var <- map toLower <$> many1 (letter <|> oneOf "+-*/!|@#$~%&/=<>")
     return $ SymbolT var

src/Parser.hs

@@ -20,7 +20,7 @@ expressionFromTokensEOF = do
 
 expressionFromTokens :: GenParser Token st Expr
 expressionFromTokens = do
-  expr <- intE <|> quotedE <|> try setE <|> try nilE <|> try consE <|> varE <|> listE
+  expr <- intE <|> quotedE <|> try setE <|> try nilE <|> try consE <|> try lambdaE <|> varE <|> listE
   return expr
 
 listE :: GenParser Token st Expr
@@ -71,6 +71,14 @@ setE = do
   _ <- parseRightParenT
   return $ SetE var expr
 
+lambdaE :: GenParser Token st Expr
+lambdaE = do
+  _ <- parseBackslashT
+  (SymbolT arg) <- parseSymbolT
+  body <- expressionFromTokens
+  return $ LambdaE arg body
+
+
 ------------------------------------------------------------
 
 satisfyT :: (Stream s m a, Show a) => (a -> Bool) -> ParsecT s u m a
@@ -78,6 +86,9 @@ satisfyT f = tokenPrim show
                        (\pos _ _ -> incSourceColumn pos 1)
                        (\t -> if f t then Just t else Nothing)
 
+parseBackslashT :: GenParser Token st Token
+parseBackslashT = satisfyT (== BackslashT)
+
 parseLeftParenT :: GenParser Token st Token
 parseLeftParenT = satisfyT (== LeftParenT)
 

src/TokenType.hs

@@ -2,6 +2,7 @@ module TokenType where
 
 data Token = LeftParenT
            | RightParenT
+           | BackslashT
            | SymbolT String
            | ApostropheT
            | IntT Integer