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MathGroup Archive 2005

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Re: this is ridiculous...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg61816] Re: this is ridiculous...
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Mon, 31 Oct 2005 01:17:09 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

On 10/30/05 at 12:43 AM, chris.chiasson at gmail.com (Chris Chiasson)
wrote:

>Can anyone replicate the pattern replacement problem I am having
>with Equal?

>In[1]:=d == 2 /. Equal[x__] :> tree[x]
>willow[d, 2] /.  willow[x__] :> tree[x]
>$Version

>Out[1]=d == 2
>Out[2]=tree[d, 2]
>Out[3]="5.2 for Microsoft Windows (June 20, 2005)"

<original replaced with InputForm to improve readability>

Yes, I get the same result. The issue is the pattern Equal[x___]. Specifically,

In[6]:=Equal[x___]
Out[6]=True

So, when Mathematica evaluates the rule, it becomes

True :> tree[x]

and since True doesn't appear in the original expression the output is Equal[d,2].

It appears what you are trying to do is change the Head of Equal[d,2]. Wouldn't it be simpler to do

tree@@Equal[d,2] ?
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