Function yield 

pub fn yield(values: Repeatable<any>) -> Repeatable<any>

Suspends the execution of the calling coroutine. Any arguments are returned as extra results by the resume that woke the coroutine up; symmetrically, yield returns the extra values passed to the next resume.

Examples

local co = coroutine.create(function(a)
  local b = coroutine.yield(a * 2)   -- b comes from the next resume
  return a + b
end)
print(coroutine.resume(co, 10))    --> true   20
print(coroutine.resume(co, 5))     --> true   15