> < ^ Date: Mon, 01 Mar 1999 11:58:07 EST
^ From: Robert Radina <radina@vmimat.mat.unimi.it >
> ^ Subject: problems with lists

My GAP version is 3.4.4.
I'm using recursively defined lists, i.e. objects of this kind:

gap> a:=[];; b:=[a];; a[1]:=b;;
gap> a; b;
[ [ ~ ] ]
[ [ ~ ] ]

I found that the basic operations don't work with these lists. For example:

gap> a=b;

causes to run out of memory. The same for:

gap> a:=[3,~];
[ 3, ~ ]
gap> a*2;

Apparently GAP tries to reach the list 'first elements' following list
structure; but this is, obviously, impossible with recursive definitions.
Now, my question is:
Is my usage of lists supported or it must be considered bad usage
(but recursion is described in the first chapter of the manual...)?
I think that if recursion is to be allowed then the function '=' must at
least report the problem and not cause exiting, wasting all the work made.

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