[rules-users] Drools as Lexer / Parser (sequential data processing)

Hello group, I recently had the idea: "A rule system (like Drools) is ideal for making programs with complex rules simpler. Writing a lexer or parser can be non-trivial. So, is it possible and also meaningful to express such a task with rules?" Anyone here who maybe tried that already? The two big questions for me are: 1) how easy is it to express a lexer with rules? 2) how bad (good?) will it perform? If you happen to have a good idea of how to do it, could you please give me an example for a simple lexer? Let's say it will get natural language (a string, such as this email) as input and should return a sequence (say, ArrayList) of Tokens, which may look like this: public class Token { public String value; public String category; Token(String value, String category) { this.value = value; this.category = category; } } We could have three categories: "word", "numeric" and "whitespace". An input String could be: "We can see 500 cars" And it should produce an ArrayList with the contents: [ Token("We", "word"), Token(" ", "whitespace"), Token("can", "word"), Token(" ", "whitespace"), Token("see", "word"), Token(" ", "whitespace"), Token("500", "numeric"), Token(" ", "whitespace"), Token("cars", "word") ] At the moment I have difficulties to see if/how this could be achieved. If you find this easy, please post a solution. I am aware that JavaCC is really good for such tasks and will also perform extremly well. Greetings, André