refactor: lexNumbers

app/Lexer.hs

@@ -26,7 +26,11 @@ lex' (x:xs) tokens orgLength = case x of
 
 lexNumbers :: String -> [Token] -> Int -> [Token]
 lexNumbers (x:xs) tokens orgLength
-    | isDigit x = lex' (dropWhile isDigit (x:xs)) ((Integer(read (takeWhile isDigit (x:xs))::Int)):tokens) orgLength
-    | otherwise = error $ "Syntax error: " ++ [x] ++ " (" ++ show (orgLength - (length (x:xs))) ++ ")"
+    | isDigit x = lex' rest ((Integer(read digits::Int)):tokens) orgLength
+    | otherwise = syntaxError x (orgLength - (length (x:xs)) + 1)
+    where
+        digits = takeWhile isDigit (x:xs)
+        rest = dropWhile isDigit (x:xs)
+        isDigit c = c `elem` "0123456789"
 
-isDigit x = x `elem` "0123456789"
+syntaxError char pos = error $ "Syntax error: " ++ [char] ++ " (" ++ show pos ++ ")"