-lex :: [Char] -> (Either String Token, [Char])
-lex [] = (Right EndOfFileToken, [])
-lex ['/':'/':xs] = lex $ dropWhile ((<>) '\n') xs
-lex ['/':'*':xs] =
- lex $ tl $ map snd $ dropWhile ((<>) ('*', '/')) $ zip2 [zero:xs] xs
-lex ['v':'a':'r':xs] = (Right VarToken, xs)
-lex ['V':'o':'i':'d':xs] = (Right VoidToken, xs)
-lex ['r':'e':'t':'u':'r':'n':xs] = (Right ReturnToken, xs)
-lex ['i':'f':xs] = (Right IfToken, xs)
-lex ['e':'l':'s':'e':xs] = (Right ElseToken, xs)
-lex ['w':'h':'i':'l':'e':xs] = (Right WhileToken, xs)
-lex ['T':'r':'u':'e':xs] = (Right TrueToken, xs)
-lex ['F':'a':'l':'s':'e':xs] = (Right FalseToken, xs)
-lex ['I':'n':'t':xs] = (Right IntTypeToken, xs)
-lex ['C':'h':'a':'r':xs] = (Right CharTypeToken, xs)
-lex ['B':'o':'o':'l':xs] = (Right BoolTypeToken, xs)
-lex [':':':':xs] = (Right DoubleColonToken, xs)
-lex ['!':'=':xs] = (Right NotEqualToken, xs)
-lex ['<':'=':xs] = (Right LesserEqToken, xs)
-lex ['>':'=':xs] = (Right GreaterEqToken, xs)
-lex ['=':'=':xs] = (Right EqualsToken, xs)
-lex ['&':'&':xs] = (Right AmpersandsToken, xs)
-lex ['|':'|':xs] = (Right PipesToken, xs)
-lex ['-':'>':xs] = (Right ArrowToken, xs)
-lex ['\'':x:'\'':xs] = (Right (CharToken x), xs)
+ret:: TokenValue [Char] Int -> (Either String Token, [Char], Int)
+ret tv rest i = (Right (i, tv), rest, i)
+
+err :: String Int -> (Either String Token, [Char], Int)
+err s i = (Left ("Line " +++ toString i +++ ": " +++ s), [], i)
+
+lex :: [Char] -> (Int -> (Either String Token, [Char], Int))
+lex [] = ret EndOfFileToken []
+lex ['/':'/':xs] = lex (dropWhile ((<>) '\n') xs)
+lex ['/':'*':xs] = \i.let (c, r) = span ((<>) ('*','/')) $ zip2 [' ':xs] xs in
+ lex (tl $ map snd $ tl $ r) (i + length [x\\(x, _)<-c | x == '\n'])
+lex ['v':'a':'r':xs] = ret VarToken xs
+lex ['V':'o':'i':'d':xs] = ret VoidToken xs
+lex ['r':'e':'t':'u':'r':'n':xs] = ret ReturnToken xs
+lex ['i':'f':xs] = ret IfToken xs
+lex ['e':'l':'s':'e':xs] = ret ElseToken xs
+lex ['w':'h':'i':'l':'e':xs] = ret WhileToken xs
+lex ['T':'r':'u':'e':xs] = ret TrueToken xs
+lex ['F':'a':'l':'s':'e':xs] = ret FalseToken xs
+lex ['I':'n':'t':xs] = ret IntTypeToken xs
+lex ['C':'h':'a':'r':xs] = ret CharTypeToken xs
+lex ['B':'o':'o':'l':xs] = ret BoolTypeToken xs
+lex [':':':':xs] = ret DoubleColonToken xs
+lex ['!':'=':xs] = ret NotEqualToken xs
+lex ['<':'=':xs] = ret LesserEqToken xs
+lex ['>':'=':xs] = ret GreaterEqToken xs
+lex ['=':'=':xs] = ret EqualsToken xs
+lex ['&':'&':xs] = ret AmpersandsToken xs
+lex ['|':'|':xs] = ret PipesToken xs
+lex ['-':'>':xs] = ret ArrowToken xs
+lex ['\'':x:'\'':xs] = ret (CharToken x) xs