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Re: MatchQ, silly question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg105114] Re: MatchQ, silly question
  • From: David Bailey <dave at removedbailey.co.uk>
  • Date: Sat, 21 Nov 2009 03:35:07 -0500 (EST)
  • References: <he5v9i$3gh$1@smc.vnet.net>

janos wrote:
> MatchQ[3 x^2, #] & /@ {3 x_^2,  3 x_^_, _ x_^_, _ _^_, _ (_^_), _ *
> (_^_)}
> 
> dives False in the last cases. Why? The FullForm
> 
> Power[Blank[ ],Plus[1,Blank[ ]]]
> 
> contains Plus, why?
> 
> Thank you.
> 
> J=E1nos
> 
Because expressions still evaluate, even if they contain Blank[] - this 
can be easily seen by entering the expression _+_ .

Wrap the pattern in HoldPattern to prevent evaluation.

David Bailey
http://www.dbaileyconsultancy.co.uk


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