The short answer is no I'm afraid. The slightly longer answer is while you can't do this, you can do something similar if you pass in a list containing a permutation, or a record with a permutation member, and change that. For example:
testperm := function(s) local i; i := 1; s[1] := s[1]^-1; Print(s,"\n"); return i; end; gap> a:=[(1,2,3)]; [ (1,2,3) ] gap> testperm(a); [ (1,3,2) ] 1 gap> a; [ (1,3,2) ] You might think, why can I change lists? The rule is you can change members of a list (or members of a record), but not the list itself. For example, if in our function we wrote ' s := [(3,2,1)] ', we would find that didn't change a, because now we are changing s, not a member of s. Chris On 19/04/2016, 22:06, "forum-boun...@gap-system.org on behalf of Rafael Villarroel" <forum-boun...@gap-system.org on behalf of rafa...@uaeh.edu.mx> wrote: > >Hello GAP forum, > >Is it possible to define a function that returns, say, an integer, but >changes a permutation given as argument, as a side effect. > >Something like this: > >testperm := function(s) > local i; > i := 1; > s := s^-1; > Print(s,"\n"); > return i; >end; > >but that when running it like this... > >gap> a:=(1,2,3); >(1,2,3) >gap> testperm(a); >(1,3,2) >1 >gap> a; >(1,2,3) > >...actually changes the permutation a. > >Thanks in advance, >Rafael > > >_______________________________________________ >Forum mailing list >Forum@mail.gap-system.org >http://mail.gap-system.org/mailman/listinfo/forum _______________________________________________ Forum mailing list Forum@mail.gap-system.org http://mail.gap-system.org/mailman/listinfo/forum
