备份-泛函编程（23）－泛函数据类型－Monad 泛函编程（23）－泛函数据类型－Monad
http://www.cnblogs.com/tiger-xc/p/4461807.html
https://blog.csdn.net/samsai100/article/details/71512702
http://www.cnblogs.com/tiger-xc/p/4461807.html
https://blog.csdn.net/samsai100/article/details/71512702