Re: Re: [Caml-list] ocamllex, regular expression syntax

[Stefan Heimann <lists@stefanheimann.net>]

Hi,

On Fri, May 23, 2003 at 08:31:39AM +0200, Pierre Weis wrote:
> 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 !)

no, the regular expression I mentioned is correct. The double quotes
do not enclose the regex but are part of it (maybe that's what
confused you):

stefan@kunz:~$ echo '"Hello \"World\"!"' | egrep
'"[^"\\]*(\\.[^"\\]*)*"'
"Hello \"World\"!"
stefan@kunz:~$ echo 'x' | egrep '"[^"\\]*(\\.[^"\\]*)*"'
stefan@kunz:~$

The single quotes just protect the string from shell expansion...

> > 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...

Normally you don't have to escape the " symbol with a backslash. Only
when you put them inside double quotes because you use the regular
expression as a normal string. But then it becomes really messy... In
ocaml's Str module syntax it looks like this:

let re = regexp "\"[^\"\\\\]*\\(\\\\.[^\"\\\\]*\\)*\""

> [...]

Bye,
  Stefan

--
Stefan Heimann
http://www.stefanheimann.net :: personal website.
http://cvsshell.sf.net       :: CvsShell, a console based cvs client.

-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners