Attempt to deconstruct Aff to either Pure or Effect

[jvliwanag]

Any chance we can get something similar to

data Step a = PureStep a | EffectStep (Effect a) | AffStep (Aff a)

deconstruct :: forall a. Aff a -> Step a

Examples:

• deconstruct (pure 5) -- returns (PureStep 5)
• deconstruct (liftEffect (log "hello world")) -- returns (EffectStep ...)

Not sure about the names. But there are incidents when I'd like to be able to take a peek at Aff a. And whether I can take advantage of JS' single threaded runtime if it turns out that the Aff is just Effect.

I can try to implement this if this change is welcome - and if it's possible.