function testPutBack()
{
$m = ['d' => '[1-9][0-9]*', 'sp' => '(\\s+)', '+'];
$lexer = new Lexer();
$lexer->init($m);
$s = $lexer->getTokenStream('1+2');
$tok = $s->fetch();
$this->assertEquals('d', $tok[0]);
$tok = $s->fetch();
$this->assertEquals('+', $tok[0]);
$s->putBack($tok);
$tok = $s->fetch();
$this->assertEquals('+', $tok[0]);
$tok = $s->fetch();
$this->assertEquals('d', $tok[0]);
$s->putBack($tok);
$tok = $s->fetch();
$this->assertEquals('d', $tok[0]);
$tok = $s->fetch();
$this->assertNull($tok);
}
