Comment by srean

Coroutine idea is very old. I am not 100% sure but they were heavily used in Telecom applications.

It's easier in C and old C++ if one can drop down to assembly to switch between different call stacks.

Among modern languages there is Lua. Take a look at Felix too.

https://felix-tutorial.readthedocs.io/en/latest/tut110.html

https://felix.readthedocs.io/en/latest/fibres.html