Coroutines in Lua

babysitter.lua

local _coroutines = {}


local _add = function(c)
  -- add a new coroutine to be "babysat"
  table.insert(_coroutines, c)
end

local _clear = function()
  -- remove all the coroutines, start afresh
  _coroutines = {}
end

local _countRunning = function()
  return #_coroutines
end

local _update = function(dt)
  -- this is where I'd really love J. Blow's 'remove' primitive...
  local i = 1
  while i <= #_coroutines do
    local c = _coroutines[i]
      -- this passes delta-time to the coroutine using Lua magic
      coroutine.resume(c, dt)
      -- remove any couroutines that have finished
      if coroutine.status(c) == "dead" then
        table.remove(_coroutines, i)
      else
        i = i + 1
      end
  end
end

return {
  add = _add,
  update = _update,
  clear = _clear,
  countRunning = _countRunning
}

main.lua

require("babysitter")

function love.keypressed(key, uni)
  -- patience is a virtue ...
  if babysitter.countRunning() > 0 then
    return
  end  

  -- wait for one second then exit
  babysitter.add(coroutine.create(function(dt)
    local t = 0
    while t < 1 do
      -- timer counts up to 1 second in total
      t = t + dt
      -- we can also fade out the music very nicely here
      music:setVolume(1 - t)
      -- resume here next update
      coroutine.yield()
    end
    love.event.push("quit")
  end))
end

function love.update(dt)
  babysitter.update(dt)
end