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MathGroup Archive 2006

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perplexed by blank sequence in pattern replacement

  • To: mathgroup at smc.vnet.net
  • Subject: [mg68674] perplexed by blank sequence in pattern replacement
  • From: "Blake" <laing at ou.edu>
  • Date: Wed, 16 Aug 2006 03:36:01 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Dear MathGroup:

I have been blithely using blank sequences in pattern matching for some
time. In persuit of a bug in a package of mine, I was quite alarmed to
find that I don't really understand how to use the blank sequence, as
expressed in the following simplified example:

In[1]:=Replace[a*b*c,Times[mysequence__]:>{mysequence}]

Out[1]={a b c}

I expected Out[1]={a,b,c}, from a naieve reading of the full form of
a*b*c

In[2]:=FullForm[a*b*c]

Out[2]//FullForm=Times[a,b,c]

Will someone PLEASE tell me why In[1] does not yield the results I
expected? (I can readily use a work-around, what I am concerned with is
a correct understanding of pattern matching).

Blake Laing
thesis slave
University of Oklahoma


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