Haskell语言学习笔记（85）STM

安装 async

$ cabal install async
async-2.2.1 installed

async 和 wait

• async :: IO a -> IO (Async a)
  启动新线程，执行异步操作。
• wait :: Async a -> IO a
  等待异步操作完成，并返回值。
• concurrently :: IO a -> IO b -> IO (a, b)
  并发（concurrently）运行两个 IO 操作，返回两个结果。