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