They're essentially callable, stateful, structured gotos. Difficult to understand for the uninitiated. For example, generators. Also known as semicoroutines.

They're essentially callable, stateful, structured gotos. Difficult to understand for the uninitiated. For example, generators. Also known as semicoroutines. https://langdev.stackexchange.com/a/834 https://langdev.stackexchange.com/a/834 This: generator fib() { a, b = 1, 2 while (a<100) { b, a = a, a+b yield a } yield a-1 } Becomes this: struct fibState { a, b, position } int fib(fibState state) { switch (fibState.postion) { case 0: fibState.a, fibState.b = 1,2 while (a<100) { fibState.b, fibState.a = fibState.a, fibState.a+fibState.b // switching the context fibState.position = 1; return fibState.a; case 1: } fibState.position = 2; return fibState.a-1 case 2: fibState.position = -1; } } The ugly state machine example presented in the article is also a manual implementation of a generator. It's as palatable to the normal programmer as raw compiler output. Being written in C++ makes it even uglier and more complicated. The programming language I made is a concrete example of what programming these things manually is like. I had to write every primitive as a state machine just like the one above. https://www.matheusmoreira.com/articles/delimited-continuations-in-lone-lisp https://www.matheusmoreira.com/articles/delimited-continuati...