Re: List manipulation question
- To: mathgroup at smc.vnet.net
- Subject: [mg15928] Re: List manipulation question
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Wed, 17 Feb 1999 23:33:59 -0500
- Organization: Universitaet Leipzig
- References: <7a2b7v$1t6@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
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