Do Modules Produce Side Effects?
- To: mathgroup at smc.vnet.net
- Subject: [mg47964] Do Modules Produce Side Effects?
- From: Harold.Noffke at wpafb.af.mil (Harold Noffke)
- Date: Tue, 4 May 2004 01:08:46 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
$Version "5.0 for Microsoft Windows [2000] (November 18, 2003)"
MathGroup:
The MathBook definition of Module tells me, "Module creates new
symbols to represent each of its local variables every time it is
called." I am led by this, and other Module descriptions, to conclude
Modules do not produce side effects, like Blocks do. However, we have
...
In[1]:= m=i^2
Out[1]= i^2
In[2]:= Module[ {}, m=4; 2*m ]
Out[2]= 8
In[3]:= m
Out[3]= 4
I expected m to remain unchanged from its original i^2. But Module
changed m to 4, just as I would expect a Block to do.
Am I misunderstanding something about the "side effect safety" of
Modules?
Regards,
Harold
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