local coroutines={}

-- starts a coroutine and returns its key
function startcoroutine(fn, key)
	add(coroutines, fn)
end

function stepcoroutine(fn)
  coresume(fn)
end

function stopcoroutine(fn)
	del(coroutines, fn)
end

function _coresolve()
  for co in all(coroutines) do
    if costatus(co)!='dead' then
      assert(coresume(co))
    else
      stopcoroutine(co)
    end
  end
end

function wait(seconds)
  wait_frames(seconds*60)
end

function wait_frames(frames)
  for i=1,frames do
    yield()
  end
end