public function __construct()
{
// init compiler/visitor if necessary
if (!self::$s_compiler) {
self::$s_compiler = Hoa\Compiler\Llk::load(new Hoa\File\Read(__CA_LIB_DIR__ . '/core/Parsers/ExpressionParser/ExpressionGrammar.pp'));
}
if (!self::$s_visitor) {
self::$s_visitor = new ExpressionVisitor();
}
}