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From: Pierre Weis <pierre.weis@inria.fr>
Message-Id: <200305230631.IAA31844@pauillac.inria.fr>
Subject: Re: [Caml-list] ocamllex, regular expression syntax
In-Reply-To: <20030522205632.GA2130@kunz.ratzer> from Stefan Heimann at "May 22, 103 10:56:33 pm"
To: lists@stefanheimann.net (Stefan Heimann)
Date: Fri, 23 May 2003 08:31:39 +0200 (MET DST)
Cc: caml-list@inria.fr
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Hi,

[...]
> But the regular expression syntax in the Str module looks "normal" to
> me.
> 
> Regular expressions like this
> 
> "[^"\\]*(\\.[^"\\]*)*"
> 
> are not easy to read,

I suppose you did not try this, since it is not a legal regular
expression. I guess you mean

"[^\\"\\]*(\\.[^\\"\\]*)*"

(Hence, the ``normal looking'' of those reg-exps does not imply simple,
clear, and natural syntax !)

> but with the ocamllex syntax it is even more
> difficult:
>
> '"'[^'"''\\']*('\\'_[^'"''\\']*)*'"'
> 
> (and harder to write).

It is not so clear to me: the ' conventions are exactly those of the
language (hence there is no need to \\ the " symbols), the _ gets its
"normal" meaning of ``whatever'' or ``catch all case'' pattern...

> Is this just for historical reason or is there a practical reason for
> this syntax? I'm just curious...

It's just natural: you would start by giving syntax to match chars,
hence you ``naturally'' write them inside quotes following the Caml
convention. The rest of the regular expressions constructs,
succession, alternative, repetitition, range and catch-all just follow
almost automatically.

Regards,

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://pauillac.inria.fr/~weis/


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