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Re: List manipulation question


Maarten.vanderBurgt at icos.be wrote:
> 
Hi Maarten,

you must give Swap23[] the attribute HoldAll to prevent the evaluation. 

SetAttributes[Swap23, HoldAll]

Swap23[l_Symbol] := 
  Module[{tmp}, tmp = l[[2]]; l[[2]] = l[[3]]; l[[3]] = tmp;]


will change the second and third entry in l. You can but you don't
need return a value because the parts of l get assigned.

Hope that helps
  Jens 

> Dear all,
> 
> In the following piece of code I define a function Swap23 which is ment
> to swap elements 2 and 3 in a list.
> Executing the function on a simple list I get an error. Why do I get
> this error? Why do I not get this error when I execute the commnad from
> Swap23 "by hand" as is shown in In[4]?
> 
> Thanks for any help
> 
> Maarten van der Burgt
> Icos Vision Systems
> Leuven
> Belgium


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