#
# This software is Copyright 2005 by Elsevier Inc.  You may use it
# under the terms of the license at http://perl.plover.com/hop/LICENSE.txt .
#



###
### alternate-continuation
###

## Chapter 8 section 8.1

sub alternate {
  my @p = @_;
  return parser { return () } if @p == 0;
  return $p[0]                if @p == 1;

  my $p;
  $p = parser {
    my ($input, $continuation) = @_;
    for (@p) {
      if (my ($v) = $_->($input, $continuation)) {
        return $v;
      }
    }
    return;  # Failure
  };
  $N{$p} = "(" . join(" | ", map $N{$_}, @p) . ")";
  return $p;
}