package Cloneable;   # interface

sub clone { die "you must implement clone() yourself" }

1; 
##</code><code>##

sub import {
  my $callerpackage = caller;

  return 1 if($locks{$callerpackage}); $locks{$callerpackage} = 1;

  # they need to finish loading before we can inspect what methods they've defined
  eval "use $callerpackage;";

  # [do the Interface validation and die if it fails...]

  undef $locks{$callerpackage};
}