When dealing with trees, it's hard to avoid recursion. And this really is a tree problem: Create a structure which has i0 children, each of which have i1 children, .., each of which has 'i(n-1)' children.

Normally, recursion can be avoided with AoA(oA(oA))) by hardcoding the for loops, because the list of loop counter vars acts as the stack recursion would give us. This doesn't apply in this case, because we have an arbitrary number of for loops.

You could avoid recursion in this case by creating an 1-dimentional array of loop counters as long as the input list, but it would overcomplicate the code for nothing. It would be fun to code it for hte challenge, but I'm late.

Update: deref can easily be rewritten to be non-recursive:

sub deref {
    my $aref = shift;
    $aref = $aref->[shift] while (@_ > 2);
    return $aref->[$_[0]] = $_[1];
}
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