[Date Index] [Thread Index] [Author Index]

Re: Pattern matches only when named

• To: mathgroup at smc.vnet.net
• Subject: [mg43877] Re: [mg43873] Pattern matches only when named
• From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
• Date: Fri, 10 Oct 2003 03:05:46 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

This works:

In[3]:=
f+g/.HoldPattern[_+_]->h

Out[3]=
h


In your second case you need HoldPattern, otherwise your pattern 
evaluates to 2 _ (2 Blank[]) which does not match anything.





On Thursday, October 9, 2003, at 02:55 PM, Ken Morgan wrote:

> Just a curiosity:
>
> In[1]:=   f + g /. u_ + _ -> h
> Out[1]:=  h
>
> but
>
> In[2]:=   f + g /. _ + _ -> h
> Out[2]:=  f + g
>
> Why does the pattern match only when one of the Blanks has a name?
>
>
> Thanks,
> Ken
>
>
>
Andrzej Kozlowski
Yokohama, Japan
http://www.mimuw.edu.pl/~akoz/
http://platon.c.u-tokyo.ac.jp/andrzej/