###
### concatenate2-continuation
###

## Chapter 8 section 8.1

sub concatenate2 {
  my ($A, $B) = @_;
  my $p;
  $p = parser {
    my ($input, $continuation) = @_;
    my ($aval, $bval);
    my $BC = parser {
      my ($newinput) = @_;
      return unless ($bval) = $B->($newinput, $continuation);
    };
    $N{$BC} = "$N{$B} $N{$continuation}";
    if (($aval) = $A->($input, $BC)) {
      return ([$aval, $bval]);
    } else {
      return;
    }
  };
  $N{$p} = "$N{$A} $N{$B}";
  return $p;
}