sub _copy {
  my $this = shift;
  if (not ref $this) {
    $this
  }
  elsif (ref $this eq "HASH") {
    +{map { $_ => _copy($this->{$_})} keys %$this}
  }
  elsif (ref $this eq "ARRAY") {
    [map _copy($_), @$this]
  }
  elsif (ref $this eq "CODE") {
    # do some processing here, the following is a 
    # placeholder
    'CODEREF'
  }
  else {
    Carp::croak "What's a " . ref $_ . "?" 
  }
}