diff --git a/app/Lexer.hs b/app/Lexer.hs
index cdf1d19..f18b11d 100644
--- a/app/Lexer.hs
+++ b/app/Lexer.hs
@@ -8,3 +8,25 @@ data Token = Plus
            | LBrace
            | RBrace
            deriving Show
+
+lex :: String -> [Token]
+lex source = reverse (lex' source [] (length source))
+
+lex' :: String -> [Token] -> Int -> [Token]
+lex' "" tokens _ = tokens
+lex' (' ':xs) tokens orgLength = lex' xs tokens orgLength
+lex' (x:xs) tokens orgLength = case x of
+    '+' -> lex' xs (Plus:tokens) orgLength
+    '-' -> lex' xs (Minus:tokens) orgLength
+    '*' -> lex' xs (Multiply:tokens) orgLength
+    '/' -> lex' xs (Divide:tokens) orgLength
+    '(' -> lex' xs (LBrace:tokens) orgLength
+    ')' -> lex' xs (RBrace:tokens) orgLength
+    _ -> lexNumbers (x:xs) tokens orgLength
+
+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 = x `elem` "0123456789"