sub TIEHANDLE
{
  my ($class, %args) = @_;
  my $handle = gensym();
  my $impl = bless { handle => gensym() }, $class;
  $impl->OPEN (%args);
  return $impl;
}

sub OPEN
{
  my ($impl, %args) = @_;
  open $impl->{handle}, $args{file} or croak "Could not open  '$args{file}'";
  $impl->{in_filter} = $args{in} || \&_no_filter;
  $impl->{out_filter} = $args{out} || \&_no_filter;
}