Re: Do Modules Produce Side Effects?

*To*: mathgroup at smc.vnet.net*Subject*: [mg48002] Re: Do Modules Produce Side Effects?*From*: Bill Rowe <readnewsciv at earthlink.net>*Date*: Wed, 5 May 2004 08:11:07 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

On 5/4/04 at 1:08 AM, Harold.Noffke at wpafb.af.mil (Harold Noffke) wrote: >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? I think you are misunderstanding the syntax of Module. To get be able to use m as a local variable and preserve global values of m, you need to specify m to be a local variable. That is you need to use the following to get the behavior you want Module[{m}, m=4; 2 m] -- To reply via email subtract one hundred and four