Lua: lua_resume and lua_yield argument purposes

Question

What is the purpose of passing arguments to lua_resume and lua_yield?

I understand that on the first call to lua_resume the arguments are passed to the lua function that is being resumed. This makes sense. However I'd expect that all subsequent calls to lua_resume would "update" the arguments in the coroutine's function. However that's not the case.

What is the purpose of passing arguments to lua_resume for lua_yield to return? Can the lua function running under the coroutine have access to the arguments passed by lua_resume?

Answer 1

What Nicol said. You can still preserve the values from the first resume call if you want:

do
  local firstcall
  function willyield(a)
    firstcall = a
    while a do
      print(a, firstcall)
      a = coroutine.yield()
    end
  end
end

local coro = coroutine.create(willyield)
coroutine.resume(coro, 1)
coroutine.resume(coro, 10)
coroutine.resume(coro, 100)
coroutine.resume(coro)

will print

1 1
10 1
100 1