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Re: Evaluation details

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86742] Re: [mg86722] Evaluation details
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Thu, 20 Mar 2008 02:52:04 -0500 (EST)
  • References: <200803191026.FAA05164@smc.vnet.net>


On 19 Mar 2008, at 11:26, Mumbo Jumbo wrote:
> Hello,
>
> I am quite puzzled why a Mathematica statement
> x=x+1;
> causes infinite recursion. Since the ducumentation states that the  
> lhs of
> this statement is not evaluated, it seems to me that the evaluation  
> of the
> rhs should not lead to recursive evaluation.
> TIA, Yuri.
>
>

The left hand side is not "pre-evaluated" but an OwnValue for x is  
created:

In[3]:= Block[{$RecursionLimit = 20}, x = x + 1]
"reclim" : "Recursion depth of   20 exceeded."
Out[3]= Hold[x + 1] + 19

In[4]:= OwnValues[x]
Out[4]= {HoldPattern[x] :> Hold[x + 1] + 19}

and then the rhs is evaluated, this OwnValue applied, a new OwnValue  
for x created etc.

Andrzej Kozlowski



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