It can be simpler to not make a finite state machine. Instead, try the different alternatives one by one, the longest one first. Instead of if (next == '

It can be simpler to not make a finite state machine. Instead, try the different alternatives one by one, the longest one first. Instead of if (next == '>') { advance() if (next == '=') { advance() return GREATER_EQUAL } else { return GREATER } } it can be simpler to do if (next is ">=") return GREATER_EQUAL if (next is ">") return GREATER The price is a little bit of performance. It needs more than one character of "lookahead" and may have to re-scan some parts of the input.