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MathGroup Archive 2004

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ReplaceList -- Unexpected Answer

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46788] ReplaceList -- Unexpected Answer
  • From: Harold.Noffke at wpafb.af.mil (Harold Noffke)
  • Date: Mon, 8 Mar 2004 04:10:23 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

MathGroup:

In The Mathematica 5 Book, Section 2.3.3 Naming Pieces of Patterns, we
find the following pattern matching exercise ...

	Now both arguments of f are constrained to be the same, and only the
	first case matches.  

	In[5]:= 
		{f[h[4], h[4]], f[h[4], h[5]]} /. f[x:h[_], x_] -> r[x]
	Out[5]= 
		{r[h[4]],f[h[4],h[5]]}


Now, let's use ReplaceList to get more insight into this matching
process ...

	In[6]:=
		ReplaceList[ {f[h[4],h[4]],f[h[4],h[5]]},f[x:h[_],x_] -> r[x] ]
	Out[6]=
		{}
		
I do not understand why ReplaceList returns {} instead of { r[h[4]] }.

Regards,
Harold


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