Be sure that finalizers can't get into a Waiting state.

[pragmatrix]

Because of #4, which effectively limits finalizers to make synchronous requests only, finalizers that get into the waiting state should not be supported. While I doubt that this is possible on a syntactical level, a dynamic check for the waiting state in debug builds should be simple to implement.

[pragmatrix]

There are other sitations in which Moms are not meant to be asynchronous (waiting for something). I see two options?

• A new type of Mom is defined which can not represent the Waiting state. This would require to duplicate a lot of functions and probably may not be usable in a transparent way as long F# does not implement traits (or we need SRTP trickery to implement that). The advantage would be that the compiler could verify if the Moms are synchronous or asynchrous.
• We could build an function that virtualizes an Mom in DEBUG builds and throws an exception if a Waiting state appears.

I'd prefer the second option for now.