Testcase parser, lexer exhausted

testcase1.pl

use Marpa::XS;
use MarpaX::Simple::Lexer;
use IO::String;

my $grammar = Marpa::XS::Grammar->new( {
    start => 'Parser',
    rules => [
        [ 'Parser'  => [ 'X' ] ],
    ],
    terminals => [qw/X/],
});

$grammar->precompute;

my $recognizer = Marpa::XS::Recognizer->new( { grammar => $grammar } );

my $lexer = MarpaX::Simple::Lexer->new(
    recognizer => $recognizer,
    tokens     => {
        X => qr/X/,
    },
    debug => 1,
);

my $io = IO::String->new("X");
$lexer->recognize($io);