Inspired by Alexey Radul's thesis on Propagation Networks

TODO:

• Propogate information
• Propagate some information
• Sing
• Speak to goblins

Other work in this area:

• Scheme: https://github.com/namin/propagators (original impl)
• Haskell: https://github.com/ekmett/propagators
• Haskell: https://github.com/typedbyte/propeller
• Scheme (implemented using spritely goblin object system): https://gitlab.com/spritely/brainy
• Python: https://github.com/duasfl8r/propagator.py
• Pure Data Scheduler C impl: (this is basically a propagator scheduler that only works on a subset of propagator types): https://github.com/pure-data/pure-data/blob/master/src/m_sched.c