# untested

sub alsoslick()
{
    if do-stuff
    {
      return dualvar 1, "SomeValue"; # or just a non-0 numeric value
    }
    else
    {
      return dualvar 0, "Some error message";
    }
}

my $result = alsoslick;
if 0+$result
{
    process( '' . $result ); # or just $result if non-error result is numeric
}
else
{
    log-error( '' . $result );
}