gistfile1.pl

sub _get_groups_data_structure {
    my ($self, $groups ) = @_;
    $groups ||= $self->groups;

    ## this implementation courtesy of ribasushi.  Must acknowledge in the
    ## paper.
    my $inject = {
        -1 => 'leaf',
        0 => { some_data => 'lvl0' },
        1 => { some_data => 'lvl1' },
    };

    my ($visit, $v);
    $v = $visit = sub {  # get $visit in scope through a hack.  Could use
                         # Sub::Current instead.  Might want to do this in the
                         # situation that this code is called in a more complex
                         # situation.
        $_[0] ||= 0;
        +{ map
               {
                   $_ => $inject->{$_[0]}
                       ? { %{$inject->{$_[0]}}, children => $visit->($_[0]+1) }
                       : $_[0] == @$groups
                           ? $visit->($_[0]+1)
                           : $inject->{-1}
                       }
                   @{$groups->[$_[0]]}
               };
    };
    weaken($visit); # without this we have a memory leak
    my $data_tree = $visit->();
    return %$data_tree;
};