use Safe;
   my $config = Safe->new;
   *{ $config->varglob($_) } = $handler{$_}
      for keys %handler;
   $ok = $config->reval( $cfg_str );
   # Or: $ok = $config->rdo( $config_source );
   $err = $@;

##</code><code>##

join ";\n", map "local *$_ = \$handler{$_}", keys %handler;

##</code><code>##

   local *handler_localizer = sub {
      if( my $name = each %handler ) {
         no strict 'refs';
         local *{$name} = $handler{$name};
         handler_localizer();
      } else {
         $ok = eval $cfg_str;
         $err = $@;
      }
   };