Create a SourceTOut, TMat which materializes a TaskCompletionSourceTResult which controls what element will be emitted by the Source. If the materialized promise is completed with a Some, that value will be produced downstream, followed by completion. If the materialized promise is completed with a None, no value will be produced downstream and completion will be signaled immediately. If the materialized promise is completed with a failure, then the returned source will terminate with that error. If the downstream of this source cancels before the promise has been completed, then the promise will be completed with None.

public static Source<T, TaskCompletionSource<T>> Maybe<T>()

static member Maybe : unit -> Source<'T, TaskCompletionSource<'T>>