Asynchronous handling

local function monsterTurn(self, completion)
    transition.to(self, {time=1000, onComplete=completion}) -- whatever actual things take care of the action here
end

local function newMonster()
    return {TakeTurn = monsterTurn}
end

local allMonsters = {}

for i=1,3 do
    allMonsters[i] = newMonster()
end

local function dmTurn(event)
    if event.choice ~= "dm" then return end
    local monstersThisTurn = {}
    for -, monster in ipairs(allMonsters) do
        monstersThisTurn[i], monstersThisTurn[monster] = monster, i
    end
    local function finishMonsterTurn(monster)
        local i = monstersThisTurn[monster]
        monstersThisTurn[monster] = nil
        table.remove(monstersThisTurn, i)
        if monstersThisTurn[1] then
            monstersThisTurn[1]:TakeTurn(finishMonsterTurn)
        else
            Runtime:dispatchEvent{name='Turn'; choice='Player'}
        end
    end
    monstersThisTurn[1]:TakeTurn(finishMonsterTurn)
end

Runtime:addEventListener('Turn', dmTurn)