Async and Promise

• proper async

• keep familiar Promise for aliased async

• Promise is implemented basically completely in userland!

• fiber-based execution (e.g. JVM's new Loom model).. but doesn't really matter, feels like TS

• (for soundness, Promis requires Copy values, which classes and primitive value types trivially satisfy)

• TS++ has no exceptions, promises never reject quite like they do in TS++

• (they're really more like Futures once you remove the exception model)

• Promise<Result<T, E>> as the result type for fallible async work

• (or Task<Result<T, E>> for affine execution)