-- coroutine.create -- 创建协程
-- coroutine.yield  -- 暂停执行 让出执行权
-- coroutine.resume -- 执行协程，继续执行协程

function foo(a)
    print("foo", a)
    return coroutine.yield(2*a)
end

co = coroutine.create(function(a, b)
    print("co-body-1", a, b)
    local r = foo(a+1)
    print("co-body-2", r)
    local r, s = coroutine.yield(a+b, a-b)
    print("co-body-3", r, s)
    return b, "end"
end)

print("main1", coroutine.resume(co, 1, 10))
print("main2", coroutine.resume(co, "r"))
print("main3", coroutine.resume(co, "x", "y"))
print("main4", coroutine.resume(co, "x1", "y1"))

--[[
执行结果：
co-body-1       1       10
foo     2
main1   true    4
co-body-2       r
main2   true    11      -9
co-body-3       x       y
main3   true    10      end
main4   false   cannot resume dead coroutine
]]