The library requires low level access to the VM, but you can yield from anywhere, and pass `coroutine.yield` as a value to higher order functions.

However, there are (were?) restrictions when C functions are present on the call stack between `coroutine.resume` and coroutine.yield`.

Edit: not that low level, actually, here's the coroutine implementation, built on top of the public Lua C API:

http://www.lua.org/source/5.3/lcorolib.c.html

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