reactive programming 1.5 monads

Data structures with map and flatMap seem to be quite common.

In fact there’s a name that describes this class of a data structures

together with some algebraic laws that they should have.

They are called monads.

带有map和flatMap的数据结构非常常见

具有这类数据结构加上一些代数规则的类就叫做monads

2. flatMap和Unit

A monad M is a parametric type M[T] with two operations, flatMap and

unit, that have to satisfy some laws.

trait M[T] {
def flatMap[U](f: T => M[U]): M[U]
}
def unit[T](x: T): M[T]

3.Examples of Monads

 List is a monad with unit(x) = List(x)Set is monad with unit(x) = Set(x)Option is a monad with unit(x) = Some(x)Generator is a monad with unit(x) = single(x)

flatMap is an operation on each of these types, whereas unit in Scala is

different for each monad

4. 在monads上用flatMap和Unit定义map

m map f == m flatMap(x => unit(f(x)))

5. monads laws

结合律

m flatMap f flatMap g == m flatMap (x => f(x) flatMap g)

左单位

unit(x) flatMap f == f(x)

右单位

m flatMap unit = m

6.monads与for表达式

结合律使得下面两个语句等价

for (y <- for (x <- m; y <- f(x)) yield y
z <- g(y)) yield z== for (x <- m;
y <- f(x)
z <- g(y)) yield z

右单元使得

for (x <- m) yield x  == m

7. Try类型

abstract class Try[+T]
case class Success[T](x: T) extends Try[T]
case class Failure(ex: Exception) extends Try[Nothing]

An expression composed from ‘Try‘, ‘map‘, ‘flatMap‘ will never

throw a non-fatal exception.

由try map flatMap构成的语句永远不会抛出非致命的异常

这个性质叫做 "bullet prooof"原理

（至今不太理解）

转载于:https://blog.51cto.com/dingbo/1591761

reactive programming 1.5 monads相关推荐

Principles of Reactive Programming 之Actors are Distributed （1）
week7中的前两节课的标题是"Actors are Distributed",讲了很多Akka Cluster的内容,同时也很难理解. Roland Kuhn并没有讲太多Akka ...
未来：spring响应式编程 Hands-On Reactive Programming in Spring 5 ，为啥需要响应式编程
Why Reactive Spring? 为什么使用响应式的spring In this chapter, we are going to explain the concept of react ...
什么是反应式编程? 这里有你想要了解的反应式编程 (Reactive programming)
理解反应式编程你曾有过订阅报纸或者杂志的经历吗?互联网的确从传统的出版发行商那儿分得了一杯羹,但是过去订阅报纸真的是我们了解时事的最佳方式.那时,我们每天早上都会收到一份新鲜出炉的报纸,并在早饭时间 ...
什么是响应式编程（Reactive Programming）
1.什么是响应式编程(Reactive Programming) Wikipedia上这样说: In computing, reactive programming is an asynchronou ...
Reactive Programming with RxJava，介绍一本书和Rx
Reactive Programming with RxJava,介绍一本书和Rx 标签(空格分隔): book RxJava Who Should Read This Book Reactive P ...
未来：spring响应式编程 Hands-On Reactive Programming in Spring 5（二）------Basic Concepts
看完这篇文章你会有很大收获! 好学近乎知,力行近乎仁,知耻而后勇. The previous chapter explained why it is important to build reacti ...
响应式编程（Reactive Programming）是什么？
简介在计算中,响应式编程(Reactive Programming)是一种面向数据流和变化传播的声明式编程范式. 这意味着可以在编程语言中很方便地表达静态或动态的数据流,而相关的计算模型会自动将变化 ...
设计模式--谈谈Reactive Programming 响应式编程
1. Reactive Programming 响应式编程 1.1. 什么是什么是响应式编程维基百科的解释如下: In computing, reactive programming is an a ...
reactive programming
In computing, reactive programming is a declarative programming paradigm concerned with data streams ...

reactive programming 1.5 monads

reactive programming 1.5 monads相关推荐

最新文章

热门文章