use Stream qw/node drop list_to_stream/;

  my @tokens = (
    node( OP  => '+' ),
    node( VAR => 'x' ),
    node( VAL =>  3  )
  );
  my $stream = list_to_stream(@tokens);

  use Data::Dumper::Simple;
  while (my $node = drop($stream)) {
    print Dumper($node, $stream);
  }

##</code><code>##

  $node   = [ 'OP', '+' ];
  $stream = [               # AoA
    [ 'VAR', 'x' ],
    [ 'VAL',  3  ]
  ];

  $node   = [ 'VAR', 'x' ]; 
  $stream = [ 'VAL',  3  ]; # not AoA

  $node   = 'VAL';
  $stream = 3;              # scalar

##</code><code>##

  my $parser = parser {
    my $input = shift;
    return unless defined $input;
    my $next = head($input);
    for my $i (0 .. $#$wanted) {
      next unless defined $wanted->[$i];
      return unless $wanted->[$i] eq $next->[$i];
    }
    my $wanted_value = $value->($next, $u);
    return ($wanted_value, tail($input));
  };

##</code><code>##

  my $parser = parser {
    my $input = shift;
    return unless defined $input;
    my $next = head($input);
    for my $i (0 .. $#$wanted) {
      next unless defined $wanted->[$i];
      return unless $wanted->[$i] eq $next->[$i];
    }
    my $wanted_value = $value->($next, $u);
    my $tail = tail($input);

    # is this the last token from the stream?
    if ($tail && 'ARRAY' eq ref $tail && 'ARRAY' ne ref $tail->[0]) {
        $tail = [ $tail ];
    }
    return ($wanted_value, $tail);
  };

##</code><code>##

  my $parser = concatenate(
    lookfor('OP'),
    lookfor('VAR'),
  );
  my ( $parsed, $remainder ) = $parser->($stream);
  is_deeply $parsed, [qw/+ x/],
    'concatenate should return the parsed values';
  is_deeply $remainder, [[ VAL => 3 ]], # AoA, not just an aref
    '... and the rest of the stream';

##</code><code>##

  $parser = concatenate(
    lookfor('OP'),
    lookfor('VAR'),
    lookfor('VAL'),
  );