Emacs Lisp编程入门指南

需积分: 9 178 浏览量更新于2024-07-27 收藏 1.44MB PDF 举报

Emacs Lisp 是一个强大的编程语言，特别与著名的文本编辑器 Emacs 紧密集成，使得用户能够在编辑器内部编写和运行代码来扩展其功能。本书《Emacs Lisp 编程入门》（An Introduction to Programming in Emacs Lisp, Revised Third Edition）由 Robert J. Chassell 编写，旨在向非程序员介绍这个主题，帮助他们理解和掌握如何在 Emacs 中进行编程。本书于 2009 年 10 月 28 日发布，版权归属于 Free Software Foundation, Inc.。作为 GNU Press 的一部分，它强调了自由软件的理念，遵循 GNU Free Documentation License，版本 1.3 或更高版本，允许用户根据这些条款复制、分发和修改文档，同时保持特定的版权和授权信息。 Emacs Lisp 的核心概念包括： 1. **环境与交互式编程**：Emacs 提供了一个高度可定制的环境，用户可以直接在编辑器中编写和测试代码，通过交互式的REPL（Read-Eval-Print Loop）进行实时反馈。 2. **宏系统**：Emacs Lisp 的宏功能允许创建自定义的编程抽象，极大地提高了代码的复用性和灵活性。 3. **模式匹配与正则表达式**：理解如何使用模式匹配和正则表达式在 Lisp 中处理文本数据是关键，这对于处理大量文本文件和文档尤其重要。 4. **数据结构与函数设计**：Emacs Lisp 提供了丰富的数据结构，如列表、字典、树等，以及用于操作这些数据的函数，有助于构建复杂的逻辑和算法。 5. **面向编辑器的编程**：Emacs Lisp 的代码通常是为编辑器本身设计的，这意味着学习者将学会如何增强编辑器的功能，比如实现新命令、自动补全、语法高亮等。 6. **文档与调试**：书中还会讲解如何阅读和理解已有的 Lisp 代码，以及如何使用内置的调试工具来排查问题。 7. **版本控制与源码管理**：虽然不是核心内容，但了解如何利用 Lisp 与版本控制系统（如 Git）集成，能更好地管理项目的开发过程。 8. **许可证和社区**：学习者还将接触到开源软件的精神和合作，以及如何参与到活跃的 Emacs Lisp 开发社区中去。如果你打算开始学习 Emacs Lisp，这本书会提供一个坚实的基础，帮助你逐渐适应这个强大且灵活的语言环境，让你能够更深入地定制和扩展你的编辑体验。

4 Preface

Thank You

My thanks to all who helped me with this boo k. My especial thanks to

Jim Blandy, Noah Friedman, Jim Kingdon, Roland McGrath, Frank Ritter,

Randy Smith, Richard M. Stallman, and Meliss a Weisshaus. My tha nks also go

to both Philip Johnson and David Stamp e fo r their patient encouragement. My

mistakes are my own.

Robert J. Chassell

bob@gnu.org

Section 1.1: Lisp Lists 1

1 List Processing

To the untutored eye, Lisp is a strange programming language. In Lisp code there

are parentheses everywhere. Some people even claim that the name stands for

‘Lots of Isolated Silly Parentheses’. But the claim is unwarranted. Lisp stands for

LISt Processing, and the programming language handles lists (and lis ts of lists) by

putting them between parentheses. The parentheses mark the boundaries of the

list. Sometimes a list is preceded by a single apostrophe or quo tation ma rk, ‘’’

Lists are the basis of Lisp.

1.1 Lisp Lists

In Lisp, a list loo ks like this: ’(rose violet daisy buttercup). This list is pr e -

ceded by a single apostrophe. It could just as well be written as follows, which looks

more like the kind of list you are likely to be familiar with:

’(rose

violet

daisy

buttercup)

The elements of this list a re the na mes of the four diﬀerent ﬂowers, separated from

each other by whitespace and sur rounded by parentheses, like ﬂowers in a ﬁeld with

a stone wa ll around them.

Lists can also have numbe rs in them, as in this lis t: (+ 2 2). This list has a

plus-sign, ‘+’, followed by two ‘2’s, each separated by whitespace.

In Lisp, both data and programs are represented the same way; that is, they a re

both lists of words, numbers, or other lists, separated by whitespa c e and surrounded

by parentheses. (Since a program looks like data, one program may easily serve

as data for another; this is a very p owerful feature of Lisp.) (Incidentally, thes e

two parenthetical remarks are not Lisp lists, because they contain ‘;’ and ‘.’ as

punctuation marks.)

Here is another list, this time with a list inside of it:

’(this list has (a list inside of it))

The components of this list are the words ‘this’, ‘list’, ‘has’, and the list ‘(a

list inside of it)’. The interior list is made up of the words ‘a’, ‘list’, ‘inside’,

‘of’, ‘it’.

1.1.1 Lisp Atoms

In Lisp, what we have been calling words are called atoms. This term comes from

the historical meaning of the word atom, which means ‘indivisible’. As far as Lisp

is concerned, the words we have been using in the lists cannot be divided into

any smalle r parts and still mean the same thing as part of a program; likewise with

numbers and single character symbols like ‘+’. On the other hand, unlike an ancient

The single apostrophe or qu otation mark is an abbreviation for the function quote; you

need not think about functions now; functions are deﬁ ned in Section 1.3 “Generate

an Error Message”, page 4.

2 Chapter 1: List Processing

atom, a list can be split into parts. (See Cha pter 7 “car cdr & cons Fundamental

Functio ns”, page 72.)

In a list, atoms ar e separated from each other by whitespace. They can be right

next to a parenthesis.

Te chnically speaking, a list in Lisp consists of par e ntheses surrounding atoms

separated by whitespace or surrounding other lists or surrounding both atoms and

other lists. A list c an have just one atom in it or have nothing in it at all. A list

with nothing in it looks like this: (), and is called the empty list. Unlike anything

else, an empty list is considered both an atom and a list at the same time.

The printed representation of both a toms and lists are called symbolic expres-

sions or, more concisely, s-expressions. The word expr ession by itself can r efer to

either the printed re presentation, or to the atom or list as it is held internally in the

computer. Often, people use the term expression indiscriminately. (Also, in many

texts, the word form is used as a syno nym for expression.)

Incidentally, the atoms that make up our universe were named such when they

were thought to be indivisible; but it has been found that physical atoms are not

indivisible. Parts can split oﬀ an atom or it can ﬁssion into two parts of roughly

equal size. Physical atoms were named pre maturely, b efore their truer nature was

found. In Lisp, certain kinds of atom, such as an array, can be separated into parts;

but the mechanism for doing this is diﬀerent from the mechanism for splitting a

list. As far as list operations are concerned, the atoms of a list are unsplittable.

As in English, the mea nings of the component letters of a Lisp atom are diﬀerent

from the meaning the letters make as a word. For example, the word for the South

American sloth, the ‘ai’, is completely diﬀerent from the two words, ‘a’, and ‘i’.

There are many kinds of atom in nature but only a few in Lisp: for ex-

ample, numbers, s uch as 37, 51 1, or 1729 , and symbols, such as ‘+’, ‘foo’, or

‘forward-line’. The words we have listed in the examples above are all symbols.

In everyday Lisp convers ation, the wor d “atom” is not often used, because program-

mers usually try to be more speciﬁc about what kind of atom they are dea ling with.

Lisp prog ramming is mostly about symbols (and sometimes numbers) within lists.

(Incidentally, the preceding three word parenthetical remark is a proper list in Lis p,

since it c onsists of ato ms , which in this case are symbols, separ ated by whitespace

and enclosed by pa rentheses, without any non-Lisp punctuation.)

Te xt between double quotation marks—even sentences or paragraphs—is also

an atom. Here is an example:

’(this list includes "text between quotation marks.")

In Lisp, all of the quoted text including the punctuation mark and the blank spaces

is a single atom. This kind of atom is called a string (for ‘string of characters’) and

is the sort of thing that is used for messages that a computer can print for a human

to read. Strings are a diﬀerent kind of atom than numbers or sy mbols a nd are used

diﬀerently.

Section 1.2: Run a Program 3

1.1.2 Whitespace in Lists

The amount of whitespace in a list does not matter. From the point of view of

the Lisp language,

’(this list

looks like this)

is exactly the same as this:

’(this list looks like this)

Both examples show what to Lisp is the same list, the list made up of the

symbols ‘this’, ‘list’, ‘looks’, ‘like’, and ‘this’ in that or der.

Extra whitespace and newlines are designed to make a list more readable by

humans . When Lisp reads the expression, it gets rid of all the extra whitespa ce

(but it needs to have at least one space between atoms in order to tell them apart.)

Odd as it seems, the examples we have seen cover almost all of what Lisp lists

look like! Every other list in Lisp looks more or less like one of these examples,

except that the list may be longer and more complex. In brief, a list is between

parentheses, a string is between quo tation marks, a symbol looks like a word, and

a number looks like a number. (For cer tain situations, square brackets, dots and

a few other special characters may be used; however, we will go quite far without

them.)

1.1.3 GNU Emacs Helps You Type Lists

When you type a Lisp ex pression in GNU Ema c s using either Lisp Interactio n mode

or Emacs Lisp mode, you have available to you several co mmands to format the Lisp

expression so it is easy to read. For example, pressing the TAB key automatically

indents the line the cursor is on by the right amount. A co mmand to properly

indent the c ode in a regio n is customarily bound to M-C-\. Indentation is designed

so that you can see which elements of a list b elong to which list—elements of a

sub-list are indented more than the elements of the enclosing list.

In addition, when you type a closing parenthesis, Emacs momentarily jumps the

cursor back to the matching o pening parenthesis, so you can see which one it is.

This is very useful, since every list you type in Lisp must have its closing pare nthesis

match its opening parenthesis. (See Section “Major Modes” in The GNU Emacs

Manual, for mor e infor mation about Emacs’ modes.)

1.2 Run a Progr am

A list in Lisp—any list—is a program ready to run. If you run it (for which the Lisp

jargon is evaluate), the computer will do one of three things: do nothing except

return to you the list itself; send you an error message; or, treat the ﬁrst symbol in

the list as a command to do something. (Usually, of cours e, it is the last of these

three things that you really want!)

The single apostrophe, ’, that I put in front of some of the example lists in

preceding sections is called a quote; w hen it precedes a list, it tells Lisp to do

nothing with the list, other than take it as it is written. But if there is no quote

preceding a list, the ﬁrst item of the list is special: it is a command for the computer

4 Chapter 1: List Processing

to obey. (In Lisp, these commands are called functions.) The list (+ 2 2) shown

above did not have a quote in front of it, so Lisp understands that the + is an

instruction to do something with the res t of the list: add the numbers that follow.

If you ar e reading this inside of GNU Emacs in Info, here is how you can evaluate

such a list: place your cursor immediately after the right hand parenthesis of the

following list and then type C-x C-e:

(+ 2 2)

You will see the number 4 appear in the echo area. (In the jargon, what you have

just done is “evaluate the list.” The echo area is the line at the bottom of the screen

that displays or “echoes” text.) Now try the same thing with a quoted list: place

the cursor right a fter the following list and type C-x C-e:

’(this is a quoted list)

You will see (this is a quoted list) appear in the echo area.

In both cases, what you are doing is giving a command to the program inside

of GNU Emacs called the Lisp interpreter—giving the interpreter a command to

evaluate the express ion. The name of the Lisp interpreter comes from the word for

the task done by a human who comes up with the meaning of an expression—who

“interprets” it.

You can also evaluate an atom that is not part of a list—one that is not sur-

rounded by parentheses; again, the Lisp interpreter translates from the humanly

readable expression to the language of the computer. But before discussing this

(see Section 1.7 “Variables”, page 9), we will discuss what the Lisp interpreter

does when you make an err or.

1.3 Generate an Error Message

Partly so you won’t worry if you do it accidentally, we will now give a command to

the Lisp interpreter that gener ates an error message. This is a harmless a c tiv ity;

and indeed, we will often try to generate error messa ges intentionally. Onc e you

understand the jargon, error messages can be informa tive. Instead of being called

“error” messages, they should be called “help” messages. They are like signposts to

a traveller in a strange country; deciphering them can be hard, but once understood,

they can point the way.

The error message is generated by a built-in GNU E macs debugger. We will

‘enter the debugger’. You get out of the debugger by typing q.

What we will do is e valuate a list that is not quoted and does not have a

meaningful command as its ﬁrs t element. Here is a list almost exactly the same as

the one we just used, but without the single-quote in front of it. Position the cursor

right after it and type C-x C-e:

(this is an unquoted list)

What you see depends on which version of Emacs you are running. GNU Emacs

version 22 provides more information than version 20 and before. First, the more

recent result of g enerating an error; then the earlier, version 20 result.

剩余269页未读，继续阅读

kexing46

粉丝: 0
资源: 2

Emacs Lisp编程入门指南

cpp-EmacsLisp编程快速指南

cpp-在EmacsLisp中的FUSE文件系统

Go-Goism在Emacs使用Go语言替代EmacsLisp语言

社区驱动的EmacsLisp编程风格指南

掌握EmacsLisp: 自定义dotfiles配置指南

Oczor一种简单的静态类型语言可编译成JavaScriptLuaRuby和EmacsLisp

改之理java源码复制-elwikicreole:EmacsLisp的WikiCreole解析器

积分兑换系统java源码-clomacs:简化EmacsLisp与Clojure的交互，反之亦然

刷题多久能面程序员-emacs-lisp-style-guide:社区驱动的EmacsLisp风格指南

EmacsLisp用户的dotfiles与src目录配置分享

最新资源