sub alpha {
    my $self = shift;
    my $condition = 1; # always
    return $self->_internal_sub($condition);
}

sub beta {
    my $self = shift;
    my $gamma = get_gamma_somewhere();
    my $condition = $self->{baz} eq $gamma;
    return $self->_internal_sub($condition);
}
sub _internal_sub {
    my $self = shift;
    my $condition = shift;
    ...
    foreach ...
        if ...
            if ...
                if ...
                    push @foo, [ @bar ] if $condition;
                }
            }
        } else {
            push @foo, [ @bar ] if $condition;
        }
    }
    push @foo, [ @bar ] if $condition;
    return \@foo;
}