paradigm/system-vs-functions
A function calculate the result of an algo. Sometimes it is called a blue function.
A system-function can have effects, and interact with the run-time. In an Actor model it is an Actor. Inparadigm/async-await it is a process yelding a result when it has finished. They are part of the system. Sometime they do not return results at all, but only interact with the system, maintaning it functional, and changing the state of the system. They are called red functions.
A red function can call blue functions, but not vice-versa.