sub all_segments {
    my $self = shift;
    return $self->_gapfill_engine('all');
}

sub all_gapfillers {
    my $self = shift;
    return $self->_gapfill_engine('gap');
}

sub _gapfill_engine {
    my $self = shift;
    my $mode = shift;
    ...
    # foreach and if loops (next stage in refactoring)
    # do one thing if $mode eq 'all'
    # do another thing if $mode eq 'gap'
    return \@segments;
}