lua中的coroutine

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


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


     print("main",coroutine.resume(co,1,10))
     print("main","z"))
     print("main","x","y"))
     print("main","y"))

结果

co-body 1 10

main false cannot resume dead coroutine

感觉上形如r = coroutine.yield()这种的r是通过下次传的参数，而不是实际的返回值。