编程与软件工程dev.stephendiehl.com
学习 Haskell 时我希望知道的事
What I Wish I Knew When Learning Haskell
2013 — 2020，它一次次回到首页
黑点是上首页（≥ 50 分）的那次投稿，空心点是没冲上去的投稿，点越大分数越高。
导读
这是 Stephen Diehl 整理的 Haskell 学习指南（以幻灯片/参考文档形式呈现），旨在让初学者快速了解学习 Haskell 时最需要知道的核心库、概念和工具。评论提到它涵盖 ACID 持久化、Pipes 流处理、Scotty Web 框架等实用库，并讨论了 monad 的教学方式。整体风格简洁全面，适合作为查阅参考。
为什么经久不衰：它用极简的示例和全面的概览，把 Haskell 生态中那些“早该知道”的库和概念集中呈现，多年间持续帮助新手跨越入门门槛，至今仍是高效的参考清单。
HN 评论精选
推荐三个能体现 Haskell 简洁威力的实用库。
我认为这三张幻灯片特别突出，它们展示了用极少的代码就能写出严肃软件：1. ACID（符合 ACID 的 Haskell 数据类型持久化，带索引）；2. Pipes（对数据流编程）；3. Scotty（微型 Web 框架，类似 Sinatra 或 Flask，构建在超快的 Warp 服务器上）。
cies查看英文原文
I think these 3 slides really stand out, they show with how little code one can write serious software in Haskell... 1. ACID (acid-compliant persistance on Haskell data types, with indexes) http://dev.stephendiehl.com/hask/#(27) 2. Pipes (program on streams of data) http://dev.stephendiehl.com/hask/#(30) 3. Scotty (micro web-framework, a la Sinatra or Flask, on top of the super fast Warp server) http://dev.stephendiehl.com/hask/#(32)
批评用抽象结构讲 monad 效果差，主张用真实代码和链式调用类比来教学。
我完全不认同他对 monad 的分析。如果只展示抽象结构，你无法理解为什么需要 do 记法这种语言级概念。这更多是例子不好的问题。用类比来表示 monad 也很糟糕，因为 Haskell 中的 monad 更多关乎编程实践而非建模真实对象。应该这样解释：展示真实代码，解释为什么用这种结构写代码。比如 jQuery 中的链式调用：$('selector').css(...).filter(...).css(...)。链式 API 有用是因为你组合计算，而不必到处传递值。Haskell 没有点号记法，但 monad 在最实用的意义上就是表示这种计算形式，最终写成 jQuery 'selector' >>= css ... >>= filter ... >>= css ...。
rtpg查看英文原文
I disagree completely with his analysis on monads. If you just present the abstract structure, you cannot understand why you even want (for example) the do notation as a language-level concept. I think this is more of a case of bad examples than anything. Trying to represnent monads via analogy works badly too though, because monads as used in haskell are more about programming pragmatics than modelling real world objects. The way to explain it should be : - Show real code - Explain why we use this structure to write our code .I think a good explanation is to ... in Jquery you do things like chaining to build things. $('selector').css('color','red').filter(someFilter).css('color','blue') Chaining APIs are useful because you're combining computation('chaining'), and you don't want to have to carry around a value everywhere. You want to do the same thing in Haskell obviously. Haskell doesn't have dot notation, so you can't do this style exactly. First idea would be to do something like let x=jQuery document selector in let y=css x 'color' 'red' in let z=filter y someFilter in ... This is a pain, especially considering that the 'chaining' here is mechanically obvious let [n+1] = f [n] [whatever] in let [n+2] = g [n+1] .... So monads, in the most pragmatic sense, allow you to represnt this form of computation. You end up with jQuery 'selector' >>= css 'color' 'red' >>= filter someSelector >>= css 'color' blue' You implicitly carry around your computation. ) In any case the Maybe monad is the worst example ever, just like how a singleton group is a bad example. Sure it's the 'simplest' , but it's far from the most typical
学习 Haskell 对任何程序员都有极高回报，推荐相关并发编程书。
真的去学就对了。很遗憾我工作中不用 Haskell，但学习 Haskell 是我做过性价比最高的事。《Parallel and Concurrent Programming in Haskell》是我读过的关于并行和并发编程概念最好的资料。每个程序员都应该学这门语言，即使他们从不打算或没机会使用它。
eklavya查看英文原文
Really just learn it. It's a pity I don't use Haskell at work and yet learning Haskell was the single most bang for buck exercise I have ever done. "Parallel and Concurrent Programming in Haskell" is the best resource I have ever read on parallel and concurrent programming concepts. Every programmer should learn this language even if they never plan/get to use it.
个人经历说明函数式编程能大幅降低状态复杂度、提升代码可重建性。
几年前我不小心把整个 Haskell 作业删了，离截止日期只剩一天。几个小时内我就从零重建了它。那时我意识到函数式编程的力量。如果用的是命令式语言，绝不可能恢复得这么快。从那以后我尽量遵循函数式风格。我意识到每个变量都是另一种状态，增加了代码的复杂度。
shahbaby查看英文原文
A few years ago I accidentally deleted my entire Haskell assignment about 1 day before it was due. Within a few hours I rebuilt it from scratch. That's when I realized the power of functional programming. There's no way I have been able to recover that quickly if I had used an imperative programming language. Since that experience I've tried to follow a functional programming style whenever I can. I've realized that every variable is another state which adds to the complexity of the code.
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