fold<R> method
Implementation
Future<R> fold<R>(R initialValue, R Function(R acc, T item) reducer) async {
var acc = initialValue;
while (!drained) {
final resultFuture = pull();
final result = resultFuture is Future ? await resultFuture : resultFuture;
acc = result.p(O.fold(() => acc, (v) => reducer(acc, v)));
}
return acc;
}