a koa style lua sample

demo.lua

-- koa style downstream and upstream

local thread1 = coroutine.create(function(down)
    print('thread1-down')
    coroutine.yield(down)
    print('thread1-up')
end)

local thread2 = coroutine.create(function(down)
    print('thread2-down')
    coroutine.yield(down)
    print('thread2-up')
end)

local arr = {
    thread1,
    function(down)
        print(1)
        down()
    end,
    thread2,
    function(down)
        print(2)
        down()
    end,
}

co(arr)()
--[[ output >>

thread1-down
1
thread2-down
2
thread2-up
thread1-up

]]

koa-style.lua

-- koa style downstream and upstream

function co(arr)
    local i = 0
    local len = #arr
    return function()
        function down(ok)
            if len <= i then return end
            i = i + 1
            local x = arr[i]
            local tp = type(x)
            if tp == 'function' then
                x(down)
            elseif tp == 'thread' then
                local chain, ret = coroutine.resume(x, down)
                if chain and ret == down then
                    down()
                    coroutine.resume(x, down)
                end
            end
        end
        down()
    end
end