Haskell趣学指南：Learn You a Haskell for Great Good

需积分: 9 150 浏览量更新于2024-07-22 1 收藏 9.99MB PDF 举报

"Learn You a Haskell for Great Good" 是一本专为初学者设计的Haskell编程语言入门指南。作者Miran Lipovac旨在通过轻松有趣的方式教授这门函数式编程语言的基础知识。在这本书中，读者将深入理解Haskell的核心概念，包括： 1. **函数式编程基础**：Haskell是一种纯函数式编程语言，这意味着所有计算都是无副作用的。书中会介绍如何定义和使用函数，以及理解函数式编程中的基本概念，如高阶函数、纯函数和不可变数据。 2. **类型系统**：Haskell拥有强大的静态类型系统，能够帮助程序员在编译时发现许多潜在错误。书中将讲解如何理解Haskell的类型推断机制，以及如何定义和使用自定义类型。 3. **模式匹配**：Haskell中模式匹配是处理数据结构的关键技术，它允许根据结构来解构值。书中会详细阐述如何使用模式匹配进行函数定义和数据操作。 4. **列表和递归**：Haskell的列表处理能力强大，主要依赖于递归。读者将学习如何使用列表和常见的列表操作，如map、filter、fold等，并了解如何编写递归函数。 5. **惰性求值**：Haskell采用惰性求值策略，意味着表达式只有在需要时才会被计算。这种特性可以有效处理无限数据结构。书中会介绍惰性求值的概念及其在实际编程中的应用。 6. **Monads**：Monads是Haskell中处理副作用和控制流的一种抽象方式，是函数式编程的重要组成部分。虽然Monads对初学者可能较为复杂，但本书会尝试以简单易懂的方式解释这一概念。 7. **类型类**：Haskell的类型类类似于其他语言的接口，提供了多态性的实现。书中会介绍如何定义和使用类型类，以及它们在代码复用和设计模式中的作用。 8. **IO操作**：尽管Haskell是纯函数式的，但仍然需要与外部世界交互。书中会讲解如何在保持函数式编程风格的同时，使用IO monad进行输入/输出操作。 9. **高级特性**：除了基础知识，书中还会涉及一些更高级的主题，如类型家族、GADTs（通用关联类型）、多参数类型类等，以帮助读者深入理解Haskell的潜力。 10. **实践应用**：通过一系列的实例和练习，读者将有机会实践所学，解决实际问题，从而巩固对Haskell的理解。 “Learn You a Haskell for Great Good”是一本全面而有趣的教程，旨在引导初学者进入Haskell的世界，同时激发他们对函数式编程的兴趣和热情。

Purely functional programming is differ-

ent. You don’t tell the computer what to do—

you tell it what stuff is. For instance, you can tell

the computer that the factorial of a number

is the product of every integer from 1 to that

number or that the sum of a list of numbers is

the ﬁrst number plus the sum of the remaining

numbers. You can express both of these opera-

tions as functions.

In functional programming, you can’t set a

variable to one value and then set it to some-

thing else later on. If you say a is 5, you can’t just change your mind and

say it’s something else. After all, you said it was 5. (What are you, some kind

of liar?)

In purely functional languages, a function has no side effects. The only

thing a function can do is calculate something and return the result. At

ﬁrst, this seems limiting, but it actually has some very nice consequences. If

a function is called twice with the same parameters, it’s guaranteed to return

the same result both times. This property is called referential transparency. It

lets the programmer easily deduce (and even prove) that a function is cor-

rect. You can then build more complex functions by gluing these simple

functions together.

Haskell is lazy. This means that

unless speciﬁcally told otherwise,

Haskell won’t execute functions

until it needs to show you a result.

This is made possible by referential

transparency. If you know that the

result of a function depends only

on the parameters that function is

given, it doesn’t matter when you

actually calculate the result of the

function. Haskell, being a lazy lan-

guage, takes advantage of this fact

and defers actually computing re-

sults for as long as possible. Once

you want your results to be displayed, Haskell will do just the bare minimum

computation required to display them. Laziness also allows you to make

seemingly inﬁnite data structures, because only the parts of the data struc-

tures that you choose to display will actually be computed.

Let’s look at an example of Haskell’s laziness. Say you have a list of num-

bers, xs = [1,2,3,4,5,6,7,8], and a function called doubleMe that doubles every

element and returns the result as a new list. If you want to multiply your list

by 8, your code might look something like this:

doubleMe(doubleMe(doubleMe(xs)))

xvi Introduction

An imperative language would probably pass through the list once, make

a copy, and then return it. It would then pass through the list another two

times, making copies each time, and return the result.

In a lazy language, calling doubleMe on a list without forcing it to show

you the result just makes the program tell you, “Yeah yeah, I’ll do it later!”

Once you want to see the result, the ﬁrst doubleMe calls the second one and

says it wants the result immediately. Then the second one says the same

thing to the third one, and the third one reluctantly gives back a doubled

1, which is 2. The second doubleMe receives that and returns 4 to the ﬁrst

one. The ﬁrst doubleMe then doubles this result and tells you that the ﬁrst ele-

ment in the ﬁnal resulting list is 8. Because of Haskell’s laziness, the doubleMe

calls pass through the list just once, and only when you really need that to

happen.

Haskell is statically typed. This means that

when you compile your program, the compiler

knows which piece of code is a number, which

is a string, and so on. Static typing means that a

lot of possible errors can be caught at compile

time. If you try to add together a number and

a string, for example, the compiler will whine

at you.

Haskell uses a very good type system that

has type inference. This means that you don’t

need to explicitly label every piece of code with a type, because Haskell’s

type system can intelligently ﬁgure it out. For example, if you say a = 5 + 4,

you don’t need to tell Haskell that a is a number—it can ﬁgure that out by

itself. Type inference makes it easier for you to write code that’s more gen-

eral. If you write a function that takes two parameters and adds them to-

gether, but you don’t explicitly state their type, the function will work on

any two parameters that act like numbers.

Haskell is elegant and concise. Because it uses a lot of high-level con-

cepts, Haskell programs are usually shorter than their imperative equiva-

lents. Shorter programs are easier to maintain and have fewer bugs.

Haskell was made by some really smart guys (with PhDs). Work on

Haskell began in 1987 when a committee of researchers got together to

design a kick-ass language. The Haskell Report, which deﬁnes a stable ver-

sion of the language, was published in 1999.

What You Need to Dive In

In short, to get started with Haskell, you need a text editor and a Haskell

compiler. You probably already have your favorite text editor installed, so we

won’t waste time on that. The most popular Haskell compiler is the Glasgow

Haskell Compiler (GHC), which we will be using throughout this book.

The best way to get what you need is to download the Haskell Platform.

The Haskell Platform includes not only the GHC compiler but also a bunch

of useful Haskell libraries! To get the Haskell Platform for your system, go to

Introduction xvii

剩余403页未读，继续阅读

Hugo_谅

粉丝: 0
资源: 1

Haskell趣学指南：Learn You a Haskell for Great Good

Haskell初学者指南：Learn You a Haskell for Great Good!

《Learn You a Haskell》：新手指南引领编程之路

入门指南：图文并茂学习Haskell编程

Learn You A Haskell For Great Good Mar 2011.pdf

learn-you-a-haskell-for-great-good:我的工作通过 Learn You a Haskell for Great Good！

向您了解Haskell的伟大成就！ -入门指南Learn You a Haskell for Great Good! - A Beginner's Guide

学习您的haskell笔记本：Jupyter改编的《 Learn a Haskell for Great Good！

学到一些Erlang，以造福所有人！Learn You Some Erlang for Great Good!

Learn_You_a_Haskell_for_Great_Good.pdf

learn-haskell:学习haskell

最新资源