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Date: -- (:)
From: Martin Jambon <martin.jambon@e...>
Subject: Re: [Caml-list] integer regular expressions
Florent.Ouchet@imag.fr wrote:
> Hello,
> 
> I'm looking for a way to match integer numbers (immediate values), whose
> types may be either int, int32, int64 or big_int. A conversion to string
> in order to use string (perl compatible) regular expressions is likely
> not the solution I'm looking for because it will not allow integer
> specific matches.
> 
> For instance (not normative), the regular expression syntax and
> semantics would allow complex matches such as "0%30" === "this integer
> matches if and only if its modulo to 30 is equal to 0". As in string
> regular expressions, operator | will implement a logical or...
> 
> I googled a little but all the results are always related to string
> regular expressions :( any pointers? any existing Caml code?

You want something called "views" or "active patterns".
You can do that in OCaml with mikmatch, which includes such syntax extension.

See http://martin.jambon.free.fr/mikmatch-manual.html#htoc10

Here is your example:

let view Mod30 = fun x -> x mod 30 = 0
(*
   but not:
     let view Mod m = fun x -> x mod m = 0

   but it could be implemented without difficulty (if really needed).
*)


let test x =
  match x with
     %Mod30 -> ...
   | ... ->


Of course the whole point is to use %Mod30 within arbitrary patterns,
otherwise it wouldn't be useful.

I you want to match regular expressions over anything else than bytes, there's
nothing out-of-the-box. You can define views on lists that would consume any
number of elements, but it is pretty limited.



Martin

-- 
http://mjambon.com/