Function co_yield 

pub fn co_yield(state: &mut LuaState) -> Result<usize, LuaError>

coroutine.yield([...]) — suspend the running coroutine.

All arguments are passed back as results of the corresponding resume.

→ return lua_yield(L, lua_gettop(L)); → lua_yield(L,n) is lua_yieldk(L, n, 0, NULL) (lua.h:316)