sub CLEAR {
    my $self = shift;
    foreach ( @$self ) {
        foreach my $key ( keys %$_ ) {
            delete $_->{ $key }
        }
    }
    $self = [ { } ];
}

##</code><code>##

sub CLEAR {
  my $self = shift;
  @$self = ( {} );
}

##</code><code>##

sub CLEAR {
  $_[0] = [ {} ];
}

##</code><code>##

use Carp;

sub push_hash (\%) {
  my $href = shift;
  my $obj = tied %$href;

  croak "must be a Tie::Hash::Stack tied hash"
    unless $obj and $obj->isa('Tie::Hash::Stack');

  push @$obj, {};
}


sub pop_hash (\%) {
  my $href = shift;
  my $obj = tied %$href;

  croak "must be a Tie::Hash::Stack tied hash"
    unless $obj and $obj->isa('Tie::Hash::Stack');

  pop @$obj;
}


# and in your program...

tie my(%stash), 'Tie::Hash::Stack';

# ...
push_hash %stash;
# ...