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From: Luc Maranget <luc.maranget@inria.fr>
Message-Id: <200210250840.KAA0000030588@beaune.inria.fr>
Subject: Re: [Caml-list] Again on pattern matching and strings
To: luther@dpt-info.u-strasbg.fr (Sven Luther)
Date: Fri, 25 Oct 2002 10:40:06 +0200 (MET DST)
Cc: luc.maranget@inria.fr (Luc Maranget),
        alex@baretta.com (Alessandro Baretta),
        garrigue@kurims.kyoto-u.ac.jp (Jacques Garrigue),
        caml-list@inria.fr (Ocaml)
In-Reply-To: <20021024162629.GA4395@iliana> from "Sven Luther" at oct 24, 2002 06:26:29 
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> > To sum it up for strings : strings are atoms to the PM compiler which
> > never look into them, it only compares one string against another, for
> > equality only.  The match compiler does not make avantage of the known
> > pattern string in any sense.  The match compiler does not make
> > avantage of the existence of a lexical ordering on strings. In fact
> > many << optimizations >> are posible here, none is performed.
> 
> So, i suppose replacing all strings in a pattern matching by an integer
> pointing to hashtable or something would improve performance a lot if
> the same string is pattern matched over and over again ?
> 
> Friendly,

Indeed, but there are other possibilities, such as tries.
In the style
match x with
| "a" -> 1
| "ab" -> 2
| "abc" -> 3
| _ -> 4

===>

switch get_char 0 x with
| 'a' ->
   begin switch get_char 1 x with
   | eos -> 1 (* end of string ... *)
   | 'b' -> (switch get_char 2 x with ...)
   | _ -> 4
   end
| _ -> 4

Where switch operates on machine integers.

> 
> Sven Luther
> 


--Luc

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