Two things: i) are you building an OO module for phylogenetics? (If yes, let's join forces); ii) here's how I did it: 
sub parent {
    my $self = $_[0];
    if ( $_[1] ) {
        my $parent = $_[1];
        if ( $parent->can('parent') ) {
            $self->[PARENT] = $parent;
        }
        else {
            my $ref = ref $self;
            carp "parents can only be $ref objects";
            return;
        }
    }
    return $self->[PARENT];
}

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This follows the "if it walks like a duck" paradigm. Not saying that this is the best way to do it, but it works for me.

In reply to Re^2: isa() on any scalar by rvosa
in thread isa() on any scalar by mrborisguy

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