public static <A, B, C> PromiseWithoutUpdates<C> lift(
final Lambda2<A, B, C> f, PromiseWithoutUpdates<A> pa, PromiseWithoutUpdates<B> pb) {
return Transaction.run(
() -> {
class Tuple {
Tuple(Optional<A> oa, Optional<B> ob) {
this.oa = oa;
this.ob = ob;
}
Optional<A> oa;
Optional<B> ob;
};
Lambda2<Tuple, Tuple, Tuple> combine =
(l, r) -> new Tuple(l.oa.isPresent() ? l.oa : r.oa, l.ob.isPresent() ? l.ob : r.ob);
Lambda1<Tuple, Optional<C>> result =
t ->
t.oa.isPresent() && t.ob.isPresent()
? Optional.of(f.apply(t.oa.get(), t.ob.get()))
: Optional.empty();
Stream<Tuple> sA = pa.sDeliver.map(a -> new Tuple(Optional.of(a), Optional.empty()));
Cell<Tuple> vA = pa.oValue.map(oa -> new Tuple(oa, Optional.empty()));
Stream<Tuple> sB = pb.sDeliver.map(b -> new Tuple(Optional.empty(), Optional.of(b)));
Cell<Tuple> vB = pb.oValue.map(ob -> new Tuple(Optional.empty(), ob));
Stream<Tuple> sAArrives = sA.snapshot(vB, combine);
Stream<Tuple> sBArrives = sB.snapshot(vA, combine);
Stream<Tuple> sSimultaneous = sA.merge(sB, combine);
Stream<C> sDeliver =
Stream.filterOptional(sAArrives.orElse(sBArrives).orElse(sSimultaneous).map(result))
.once();
Cell<Optional<C>> oValue = Cell.lift(combine, vA, vB).map(result);
return new PromiseWithoutUpdates<C>(sDeliver, oValue);
});
}
static <A> Cell<List<A>> sequence(Collection<Cell<A>> in) {
Cell<List<A>> out = new Cell<>(new ArrayList<A>());
for (Cell<A> c : in)
out =
Cell.lift(
(l0, a) -> {
List<A> l = new ArrayList<A>(l0);
l.add(a);
return l;
},
out,
c);
return out;
}