while ( @list ) {
      $x = shift(@list);
      ($a,$b) = @$x;

      if ( ref($a) eq "CODE" ) {
          &$a($b); # modifies @list
      } else {
           $a->$b; # $a may be a class or an object;
                   # modifies @list 
      }
} # end of evil code that tells me nothing