[pmahoney]

Here is (I think) the example regex ported to OCaml's Re library [1]

    let my_regex =
      let open Re in
      seq [
          bos;
          opt (str "0x");
          repn (
              alt [
                  rg 'A' 'F';
                  rg 'a' 'f';
                  rg '0' '9';
              ]
          ) 4 None |> group;
          eos;
      ]
      |> compile

I'm familiar with standard (compact) regex syntax, but I've been using the above syntax recently in a couple small places. I'm a bit on the fence as to which is "better". The compact syntax is, of course, more compact. I think it's a very similar comparison between APL (which I've not used) and most other common programming languages.

One advantage of the expanded syntax is that it's a bit nicer to incorporate a string variable, e.g. "str some_string" vs. "/#{Regexp.escape(some_string)}/" (to borrow Ruby's syntax).

[1] https://github.com/ocaml/ocaml-re