Deferred

Creates an unset Deferred.
Every time you bind the resulting F, a new Deferred is created.
If you want to share one, pass it as an argument and flatMap
once.

Like apply but returns the newly allocated Deferred directly
instead of wrapping it in F.delay. This method is considered
unsafe because it is not referentially transparent -- it
allocates mutable state.
In general, you should prefer apply and use flatMap to get state sharing.

Like apply but initializes state using another effect constructor