Programming in Emacs Lisp : an introduction

262 Pages·1997·0.925 MB·English

by  Robert J Chassell, Free Software Foundation (Cambridge, Mass.)

Programming in Emacs Lisp
An Introduction

Programming in Emacs Lisp
An Introduction
Edition 1.05, 21 October 1997
by Robert J. Chassell
Copyright (cid:13)c 1990, ’91, ’92, ’93, ’94, ’95, ’97 Free Software Foundation, Inc.
Published by the Free Software Foundation, Inc.
59 Temple Place, Suite 330
Boston, MA 02111-1307 USA
ISBN-1882114-41-8
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i
Short Contents
Preface......................................... ix
1 List Processing................................. 1
2 Practicing Evaluation ........................... 19
3 How To Write Function Definitions .................. 25
4 A Few Buffer–Related Functions.................... 45
5 A Few More Complex Functions .................... 55
6 Narrowing and Widening......................... 67
7 car, cdr, cons: Fundamental Functions ............. 71
8 Cutting and Storing Text......................... 79
9 How Lists are Implemented ....................... 97
10 Yanking Text Back ............................ 101
11 Loops and Recursion ........................... 105
12 Regular Expression Searches...................... 121
13 Counting: Repetition and Regexps.................. 137
14 Counting Words in a defun...................... 149
15 Readying a Graph............................. 167
16 Your ‘.emacs’ File............................ 177
17 Debugging .................................. 191
18 Conclusion.................................. 197
Appendix A The the-the Function .................. 199
Appendix B Handling the Kill Ring ................... 201
Appendix C A Graph with Labelled Axes ............... 211
Index......................................... 233
ii Programming in Emacs Lisp
iii
Table of Contents
Preface ...................................... ix
For Whom This is Written.................................... x
Lisp History ................................................ xi
A Note for Novices.......................................... xi
Thank You ................................................. xi
1 List Processing ............................ 1
1.1 Lisp Lists............................................... 1
1.1.1 Lisp Atoms .................................... 1
1.1.2 Whitespace in Lists............................. 2
1.1.3 GNU Emacs Helps You Type Lists............... 3
1.2 Run a Program......................................... 3
1.3 Generate an Error Message .............................. 4
1.4 Symbol Names and Function Definitions .................. 5
1.5 The Lisp Interpreter..................................... 5
1.5.1 Byte Compiling................................. 6
1.6 Evaluation.............................................. 6
1.6.1 Evaluating Inner Lists .......................... 7
1.7 Variables............................................... 8
1.7.1 Error Message for a Symbol Without a Value..... 9
1.8 Arguments.............................................. 9
1.8.1 Arguments’ Data Types........................ 10
1.8.2 An Argument as the Value of a Variable or List.. 11
1.8.3 Variable Number of Arguments................. 11
1.8.4 Using the Wrong Type Object as an Argument .. 11
1.8.5 The message Function......................... 12
1.9 Setting the Value of a Variable.......................... 14
1.9.1 Using set..................................... 14
1.9.2 Using setq.................................... 15
1.9.3 Counting...................................... 15
1.10 Summary............................................. 16
1.11 Exercises............................................. 17
2 Practicing Evaluation ..................... 19
2.1 Buffer Names.......................................... 19
2.2 Getting Buffers ........................................ 21
2.3 Switching Buffers ...................................... 22
2.4 Buffer Size and the Location of Point.................... 23
2.5 Exercise............................................... 23
iv Programming in Emacs Lisp
3 How To Write Function Definitions ........ 25
3.1 The defun Special Form................................ 25
3.2 Install a Function Definition ............................ 27
3.2.1 Change a Function Definition................... 28
3.3 Make a Function Interactive ............................ 28
3.3.1 An Interactive multiply-by-seven.............. 29
3.4 Different Options for interactive ...................... 30
3.5 Install Code Permanently............................... 31
3.6 let ................................................... 32
3.6.1 The Parts of a let Expression.................. 32
3.6.2 Sample let Expression......................... 33
3.6.3 Uninitialized Variables in a let Statement....... 34
3.7 The if Special Form ................................... 34
3.7.1 The type-of-animal Function in Detail......... 35
3.8 If–then–else Expressions................................ 36
3.9 Truth and Falsehood in Lisp............................ 37
3.10 save-excursion...................................... 38
3.10.1 Template for a save-excursion Expression .... 39
3.11 Review............................................... 40
3.12 Exercises............................................. 43
4 A Few Buffer–Related Functions........... 45
4.1 Finding More Information .............................. 45
4.2 A Simplified beginning-of-buffer Definition............ 45
4.3 The Definition of mark-whole-buffer................... 47
4.3.1 Body of mark-whole-buffer................... 48
4.4 The Definition of append-to-buffer .................... 48
4.4.1 The append-to-buffer Interactive Expression... 49
4.4.2 The Body of append-to-buffer................ 50
4.4.3 save-excursion in append-to-buffer.......... 50
4.5 Review................................................ 52
4.6 Exercises.............................................. 53
5 A Few More Complex Functions........... 55
5.1 The Definition of copy-to-buffer....................... 55
5.2 The Definition of insert-buffer........................ 56
5.2.1 The Interactive Expression in insert-buffer.... 56
A Read-only Buffer............................ 56
‘b’ in an Interactive Expression................. 57
5.2.2 The Body of the insert-buffer Function....... 57
5.2.3 insert-buffer With an if Instead of an or..... 57
5.2.4 The or in the Body............................ 58
5.2.5 The let Expression in insert-buffer.......... 59
5.3 Complete Definition of beginning-of-buffer............ 60
5.3.1 Optional Arguments........................... 61
5.3.2 beginning-of-buffer with an Argument....... 62
What happens in a large buffer................. 62
What happens in a small buffer................ 63
5.3.3 The Complete beginning-of-buffer........... 64
5.4 Review................................................ 65
5.5 &optional Argument Exercise .......................... 65
v
6 Narrowing and Widening.................. 67
6.1 The save-restriction Special Form.................... 67
6.2 what-line............................................. 68
6.3 Exercise with Narrowing................................ 69
7 car, cdr, cons: Fundamental Functions ..... 71
7.1 car and cdr........................................... 71
7.2 cons.................................................. 72
7.2.1 Find the Length of a List: length.............. 73
7.3 nthcdr................................................ 74
7.4 setcar................................................ 76
7.5 setcdr................................................ 76
7.6 Exercise............................................... 77
8 Cutting and Storing Text ................. 79
8.1 zap-to-char .......................................... 80
8.1.1 The interactive Expression................... 80
8.1.2 The Body of zap-to-char...................... 81
8.1.3 The search-forward Function ................. 81
8.1.4 The progn Function ........................... 82
8.1.5 Summing up zap-to-char ..................... 83
8.1.6 The Version 18 Implementation................. 83
The body of the progn expression.............. 84
8.2 kill-region .......................................... 86
8.3 delete-region: A Digression into C .................... 86
8.4 Initializing a Variable with defvar ...................... 88
8.5 copy-region-as-kill.................................. 89
8.5.1 The Body of copy-region-as-kill............. 90
The kill-append function..................... 91
The else-part of copy-region-as-kill......... 92
8.6 Review................................................ 94
8.7 Searching Exercises..................................... 96
9 How Lists are Implemented ............... 97
9.1 Exercise.............................................. 100
10 Yanking Text Back ..................... 101
10.1 Kill Ring Overview................................... 101
10.2 The kill-ring-yank-pointer Variable ............... 101
10.3 Exercises with yank and nthcdr....................... 103
vi Programming in Emacs Lisp
11 Loops and Recursion.................... 105
11.1 while............................................... 105
11.1.1 A while Loop and a List..................... 106
11.1.2 An Example: print-elements-of-list ...... 107
11.1.3 A Loop with an Incrementing Counter........ 108
Example with incrementing counter ........... 108
The parts of the function definition............ 109
Putting the function definition together........ 110
11.1.4 Loop with a Decrementing Counter........... 112
Example with decrementing counter........... 112
The parts of the function definition............ 113
Putting the function definition together........ 113
11.2 Recursion ........................................... 114
11.2.1 Recursion with a List........................ 115
11.2.2 Recursion in Place of a Counter .............. 116
An argument of 3............................ 117
11.2.3 Recursion Example Using cond............... 118
11.3 Looping Exercise..................................... 119
12 Regular Expression Searches ............ 121
12.1 The Regular Expression for sentence-end............. 121
12.2 The re-search-forward Function..................... 122
12.3 forward-sentence................................... 123
The while loops............................. 124
The regular expression search................. 126
12.4 forward-paragraph: a Goldmine of Functions ......... 126
The let* expression.......................... 127
The forward motion while loop............... 129
Between paragraphs.......................... 130
Within paragraphs........................... 131
No fill prefix................................. 131
With a fill prefix............................. 132
Summary.................................... 132
12.5 Create Your Own ‘TAGS’ File.......................... 134
12.6 Review.............................................. 134
12.7 Exercises with re-search-forward.................... 136
13 Counting: Repetition and Regexps ...... 137
13.1 The count-words-region Function ................... 137
13.1.1 The Whitespace Bug in count-words-region.. 140
13.2 Count Words Recursively............................. 142
13.3 Exercise: Counting Punctuation....................... 147