lexer can now read single character tokens

src/lexer/lexer.cpp

@@ -0,0 +1,34 @@
+#include "lexer.hpp"
+
+#include "token/token.hpp"
+
+#include <iostream>
+
+namespace lexer {
+    token::token lexer::next_token() {
+        char c;
+        if (!(input >> c))
+            return {token::type::END_OF_FILE, ""};
+
+        switch (c) {
+        case '=':
+            return {token::type::ASSIGN, c};
+        case '+':
+            return {token::type::PLUS, c};
+        case ',':
+            return {token::type::COMMA, c};
+        case ';':
+            return {token::type::SEMICOLON, c};
+        case '(':
+            return {token::type::LPAREN, c};
+        case ')':
+            return {token::type::RPAREN, c};
+        case '{':
+            return {token::type::LBRACE, c};
+        case '}':
+            return {token::type::RBRACE, c};
+        }
+        return {token::type::ILLEGAL, c};
+    };
+
+} // namespace lexer