Make custom monads available.

[ゆきくらげ]

I'd like to do away with contexts and allow custom monads to be used in apps like Halogen.
I think this requires abstraction of operations, but I have no idea how to do it...

[ゆきくらげ]

This seems a bit difficult, so I'll give up on including it in v0.7.

[ゆきくらげ]

I think this class is important. 🤔

class MonadEffect m <= MonadSequenceSignal m where
  sequenceSignal :: Signal (m a) -> m (Signal a)

This indicates that the Signal can be unwrapped.
If this can be done, arbitrary Hooks could be embedded.

The problem is that if m is a MonadSequenceSignal, then FreeT f m must also be a MonadSequenceSignal.
This is because it allows the Component to be a MonadSequenceSignal as well.

[ゆきくらげ]

b08db91