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MathGroup Archive 2000

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Re: With[{software=Mathematica}, Frustration]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24335] Re: [mg24308] With[{software=Mathematica}, Frustration]
  • From: BobHanlon at aol.com
  • Date: Sun, 9 Jul 2000 04:52:43 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

In a message dated 7/7/2000 12:44:38 AM, siegman at stanford.edu writes:

>Pages 359-360 of The Mathematica Book says (admittedly, taken a little
>
>out of context), 
>
>   "You can think of  With  as a generalization of the /. operator. . ."
>
>and
>
>   " With[{x=x0}, body]  works essentially like body /. x->x0 . . . "
>
>Great, looks neat, let's try it for evaluating expressions without 
>permanently setting the variables in them:
>
>   In[1]:= c = a b
>
>   Out[1]= a b
>
>   In[2]:= c
>
>   Out[2]= a b
>
>   In[10]:= c /. {a -> 2, b -> 3}
>
>   Out[10]= 6
>
>   In[3]:= With[{a = 2, b = 3}, c]
>
>   Out[3]= a b
>
>*Not* what I was hoping for  . . .
>

Attributes[With]

{HoldAll, Protected}

c = a*b;

With[{a = 2, b = 3}, Evaluate[c]]

6


Bob Hanlon


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