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Date: Sat, 30 Jun 2007 10:19:37 +0200
From: Pierre =?ISO-8859-15?B?RXRjaGVtYe906Q==?= <petchema@concept-micro.com>
To: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] The Implicit Accumulator: a design pattern using
 optional arguments
Message-Id: <20070630101937.a95e7e6c.petchema@concept-micro.com>
In-Reply-To: <200706271453.06045.jon@ffconsultancy.com>
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	<1A1D6F56-B3DB-4552-969C-9859482175AC@lrde.epita.fr>
	<200706271453.06045.jon@ffconsultancy.com>
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Le Wed, 27 Jun 2007 14:53:05 +0100, Jon Harrop <jon@ffconsultancy.com> a écrit :

> 
> # let symbol =
>     let m = Hashtbl.create 1 in
>     fun string ->
>       try Hashtbl.find m string with Not_found ->
>       Hashtbl.add m string string;
>       string;;
> val symbol : '_a -> '_a = <fun>

The usual way to do this in OCaml is using a weak hashtable. Benefit is
that the strings can still be collected when not longer used. Weak
hashtables also have a "merge" function that do exactly what we want:

module H = Weak.Make(struct
        type t = string
        let hash = Hashtbl.hash
        let equal (x:t) y = x = y
      end)

let symbol =
  let symbols = H.create 13 in
  H.merge symbols