callback
https://peps.python.org/pep-0255/
continuation passing style (CPS)
state machine
generators are used to easily create iterators; coroutines are used to introduce concurrency or complex control flows. https://faculty.ai/tech-blog/flow-types-for-generators-and-coroutines-in-javascript/
https://flow.org/blog/2015/11/09/Generators/