Re: Problem with matching.

*To*: mathgroup at smc.vnet.net*Subject*: [mg54017] Re: [mg53907] Problem with matching.*From*: Josef Karthauser <joe at tao.org.uk>*Date*: Mon, 7 Feb 2005 03:13:18 -0500 (EST)*References*: <200502040911.EAA00959@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Thanks to everyone who had suggestions to address my matching problem. The boiled down wisdom is that in the case where a pattern doesn't appear to match in the way expected, e.g.. in MatchQ[expr,pattern], make use of both 'expr//FullForm' and 'pattern//FullForm' to make sure that both the expression and the pattern are really in the form that you expect, because other rules might have had a chance to rewrite them before they get applied. Copious amounts of 'HoldPattern[pattern]' might be necessary to get the expected behaviour. Rgds, Joe On Fri, Feb 04, 2005 at 04:11:08AM -0500, Bob Hanlon wrote: > F[{___,a_,___}]F[{___,a_,___}]//FullForm > > Power[F[List[BlankNullSequence[],Pattern[a,Blank[]],BlankNullSequence[]]],2] > > The two terms on the LHS of the rule are identical so they are multiplied to > form F^2. Use the following: > > F[{x,2,c}]F[{x,1,f}]/.F[{___,a_,___}]F[{___,b_,___}]/;a==b:>yes > > yes > > > Bob Hanlon > > > > > From: Josef Karthauser <joe at tao.org.uk> To: mathgroup at smc.vnet.net > > Date: 2005/02/02 Wed PM 06:10:51 EST > > To: mathgroup at smc.vnet.net > > Subject: [mg54017] [mg53913] [mg53907] Problem with matching. > > > > Can someone tell me why this doesn't match? > > > > F[{x, 2, c}]F[{x, 1, f}] /. F[{___, a_, ___}]F[{___, a_, ___}] :> yes > > > > I'm expecting 'yes' to be returned if any of the list arguments to F[] > > contain the same value. It doesn't match however; what am I doing > > wrong? > > > > Thanks, > > Joe -- Josef Karthauser (joe at tao.org.uk) http://www.josef-k.net/ FreeBSD (cvs meister, admin and hacker) http://www.uk.FreeBSD.org/ Physics Particle Theory (student) http://www.pact.cpes.sussex.ac.uk/ ================ An eclectic mix of fact and theory. =================

**References**:**Re: Problem with matching.***From:*Bob Hanlon <hanlonr@cox.net>