RE: Pattern matches only when named
- To: mathgroup at smc.vnet.net
- Subject: [mg43894] RE: [mg43873] Pattern matches only when named
- From: "David Park" <djmp at earthlink.net>
- Date: Fri, 10 Oct 2003 03:06:04 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Ken, Because the lhs of the rule is evaluated by Mathematica giving 2_. _ + _ -> h 2 _ -> h And that doesn't match anything in your expression. Use HoldPattern to prevent evaluation. f + g /. HoldPattern[ _ + _] -> h h David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: Ken Morgan [mailto:kemorgan at vt.edu] To: mathgroup at smc.vnet.net 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