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Re: Why does _+_==2_ (or, why is HoldPattern required

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  • Subject: [mg132245] Re: Why does _+_==2_ (or, why is HoldPattern required
  • From: Alan G Isaac <alan.isaac at gmail.com>
  • Date: Wed, 22 Jan 2014 03:31:46 -0500 (EST)
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On 1/20/2014 10:42 PM, Itai Seggev wrote:
> MatchQ[x+x, _+_] would return False


That is actually much less surprising to me:
one expects evaluation of the first expression.
What is quite surprising is that `_+_` does
not stand for any+thing, `_*_` does
not stand for any*thing, etc.
(Not unless one uses HoldPattern.)
I do not consider these "edge cases".

As you say, a decision had to be made.
I am just trying to understand the decision.
Your answer that it treats all symbolic expressions
equally is very likely a good answer in the end,
but of course on its own it begs the question.

Thanks,
Alan Isaac




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