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.