备忘
http://www.jdon.com/idea/monad.html
http://blog.leichunfeng.com/blog/2015/11/08/functor-applicative-and-monad/
http://www.jdon.com/idea/functor-monad.html
http://www.jdon.com/designpatterns/functional-patterns-identity.html
http://www.jdon.com/idea/monoid.html
http://www.jdon.com/idea/monad.html
https://www.cnblogs.com/wujy/p/4950591.html
https://www.jianshu.com/p/e0b0afd0519f
http://blog.csdn.net/chenyin10011991/article/details/51971388
https://www.raywenderlich.com/62699/reactivecocoa-tutorial-pt1
我思故我在