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MathGroup Archive 1998

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Re: How to change the argument of a function?



Vilis Nams wrote:
> 
> I want to define a function that in the course of doing something, also
> changes the value of its argument, for example: f[x_]:=Module[{},
> x=2*x;
> x
> ]
> When I run the function, I get the error: "Set::setraw : Cannot assign
> to raw object  ...." Can this be done in some way?
> 
> --------------------
> Vilis O. Nams
> Dept of Biology, NSAC
> Box 550, Truro, NS,  Canada
> vnams @ nsac.ns.ca
> -------------------


If I have an argument I want to change in the course of a functional
evaluation, I make a "working" copy at the beginning of the function:

f[x_]:=Module[{y},
  y=x;
> y=2*y;
> y
> ]

I don't think you can change the value of the actual argument inside a
function, or if you could that it would be a good idea.  If you made
global changes inside a local function, it might make for some
interesting bugs that would be very hard to track down. -- 
Remove the _nospam_ in the return address to respond.



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