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MathGroup Archive 1998

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Re: Disappearing variables

  • To: mathgroup at smc.vnet.net
  • Subject: [mg13801] Re: [mg13759] Disappearing variables
  • From: BobHanlon at aol.com
  • Date: Fri, 28 Aug 1998 04:18:24 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

f:=x=123

?f

"Global`f"

f := x = 123

f

123

x

123

Remove[x]

Removing x changed the definition for f:

?f

"Global`f"

f := Removed["x"] = 123

f

123

x is no longer in the definition of f; consequently, the call for f did
not re-assign the value to x

x

x

Bob Hanlon

In a message dated 8/24/98 6:51:01 AM, nobody at News.Dal.Ca wrote:

>I want to to define a variable inside a function, as follows: f:=x=123;
>Whenever I run f, x should be given the value of 123, and if x doesn't
>exist, it should be created. However:
>
>In[1]:= f:=x=123;
>In[2]:=f
>Out[2]:=123
>In[3]:=x
>Out[3]:=123        ** x exists
>In[4]:=Remove[x];
>In[5]:=f
>Out[5]:=123  ** f seems to work 
>In[6]:=x
>Out[6]:=x     ** x doesn't exist anymore, even though f worked
>
>It seems like x is created when I initially define f, whereas since f is
>SetDelayed,  x should be created when I run f.  Does anyone know why x
>is not created when I run f?


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