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Re: ClearAll error message

  • To: mathgroup at smc.vnet.net
  • Subject: [mg92356] Re: ClearAll error message
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Mon, 29 Sep 2008 07:05:38 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <gbnpep$pr3$1@smc.vnet.net>

carlos at colorado.edu wrote:
> Just out of curiosity.  The following ClearAll works as expected.
> 
>   name=Symbol["A"]; ClearAll[name];
> 
> But this elicits an error message:
> 
>   ClearAll[Symbol["A"]];
> 
> Why?  A non-standard argument evaluation?

*snip*

Correct: ClearAll does not evaluate its argument(s) (attribute *HoldAll*).


     In[1]:= ClearAll[Symbol["A"]]

     During evaluation of In[1]:= ClearAll::ssym: Symbol[A] is not
     a symbol or a string.

     In[2]:= Attributes[ClearAll]

     Out[2]= {HoldAll, Protected}

     In[3]:= ?HoldAll

     HoldAll is an attribute which specifies that all arguments to
     a function are to be maintained in an unevaluated form.


Regards,
-- Jean-Marc


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