Oh, I was talking much more about how you can first learn how to write a compiler. I wasn't talking about how you write a production industry-strength compiler.

Btw, I mentioned parser combinators: those are basically just a front-end. Similar to regular expressions. The implementation can be all kinds of things, eg could be recursive descent or a table or backtracking or whatever. (Even finite automata, if your combinators are suitably restricted.)

I used a small custom parser combinator library to parse Fortran from raw characters (since tokenization is so context-dependent), and it's worked well.