query method

Implementation

@override
Stream<Node> query(Database database) async* {
  Stream<Node> solutions(int index, Map<Variable, Node> bindings) async* {
    if (index < arguments.length) {
      final arg = arguments[index];
      final subs = arg.substitute(bindings) as Term;
      await for (final item in database.query(subs)) {
        final unified = mergeBindings(arg.match(item), bindings);
        if (unified != null) {
          yield* solutions(index + 1, unified);
        }
      }
    } else {
      yield substitute(bindings);
    }
  }

  yield* solutions(0, newBindings());
}