Re: Pattern match exactly 0 or 1 times?
- To: mathgroup at smc.vnet.net
- Subject: [mg26410] Re: Pattern match exactly 0 or 1 times?
- From: Rainer Gruber <rainer.gruber at jk.uni-linz.ac.at>
- Date: Wed, 20 Dec 2000 00:21:34 -0500 (EST)
- Organization: Johannes Kepler Universitaet Linz
- References: <91f70k$548@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi Gavin,
I think you are searching for something like this:
In[1]:=
f[x___ /; Length[{x}] <= 1] := something
The additional condition make sure that only if f has 0 or 1 arguments
it is evaluted to "someting".
Rainer Gruber
Gavin Scott wrote:
>
> Is there a way to specify a pattern which will match exactly zero or
> one times? I find myself wanting somethinglike the standard regular
> expression '?' operator, but can't see a way to do this with
> Mathematica's pattern features. The closest I've been able to come
> is something like:
>
> x___ /; x=="a"
>
> which will match zero or more copies of a specific value. I'd like
> to match no more than one though.
>
> Is there anything like a general Regular Expression package for
> Mathematica anywhere? I did a quick search and didn't find anything
> like this, so I'm wondering if my desire for such a thing simply
> indicates that there's something fundamental about Mathematica
> that I don't get yet which would eliminate the need for this.
>
> Thanks,
>
> G.