###
### T-continuation
###

## Chapter 8 section 8.1

sub T {
  my ($parser, $transform) = @_;
  my $p = sub {
    my ($input, $continuation) = @_;
    if (my $v = $parser->($input, $continuation)) {
      $v = $transform->(@$v);
      return $v;
    } else {
      return;
    }
  };
  $N{$p} = $N{$parser};
  return $p;
}