sub map_constant_name {
  my ($name) = @_ ;

  # Let's not eval anything other than a simple name !

  if ($name !~ /^\w+$/) {
    $@ = "will not map '$name'" ;
    return undef ;
  } ;

  # OK -- eval to try to get constant value

  my $val = eval "$name()" ;

  return $@ ? undef : $val ;
} ;