# Learning J

tenth draft, February 2005
About this Book
Table of Contents
Acknowledgements
Recent Changes
Index

J software and documentation are available at | J Software Home Page
This book is also available as a | single downloadable zip file
There is a version in PDF format at | Skip Cave's web page
Please send comments and criticisms to the | J Forum

### ABOUT THIS BOOK

This book is meant to help the reader to learn the computer-programming language J.

The book is intended to be read with enjoyment by both the beginning programmer and the experienced programmer alike. The only prerequisite is an interest on the part of the reader in learning a programming language.

The emphasis is on making the J language accessible to a wide readership. Care is taken to introduce only one new idea at a time, to provide examples at every step, and to make examples so simple that the point can be grasped immediately. Even so, the experienced programmer will find much to appreciate in the radical simplicity and power of the J notation.

The scope of this book is the core J language common to the many implementations of J available on different computers. The coverage of the core language is meant to be relatively complete, covering (eventually) most of the J Dictionary.

Hence the book does not cover topics such as graphics, plotting, GUI, and database access covered in the J User Guide. It should also be stated what the aims of the book are not: neither to teach principles of programming as such, nor to study algorithms, or topics in mathematics or other subjects using J as a vehicle, nor to provide definitive reference material.

The book is organized as follows. Part 1 is an elementary introduction which touches on a variety of themes. The aim is to provide the reader, by the end of Part 1, with an overview and a general appreciation of the J language. The themes introduced in Part 1 are then developed in more depth and detail in the remainder of the book.

## TABLE OF CONTENTS

### Part 1: Getting Acquainted

1: Basics
2: Lists and Tables
3: Defining Functions
4: Scripts and Explicit Functions

### Part 2: Arrays

5: Building Arrays
6: Indexing
7: Ranks

### Part 3: Defining Functions: Verbs

8: Composing Verbs
9: Trains of Verbs
10: Conditional and Other Forms
11: Tacit Verbs Concluded
12: Explicit Verbs

### Part 4: Defining Functions: Operators

13: Explicit Operators
14: Gerunds
15: Tacit Operators

### Part 5: Structural Functions

16: Rearrangements
17: Patterns of Application
18: Sets, Classes and Relations

### Part 6: Numerical and
Mathematical Functions

19: Numbers
20: Scalar Numerical Functions
21: Factors and Polynomials
22: Vectors and Matrices
23: Calculus

### Part 7: Names and Objects

24: Names and Locales
25: Object-Oriented Programming

### Part 8: Facilities

26: Script Files
27: Representations and Conversions
28: Data Files
29: Error Handling

### Appendices

A1: Evaluating Expressions
A2: Collected Terminology
Index

### Recent Changes

Clarifications and corrections in a number of chapters. The index has been improved.

### Acknowledgements

I am grateful to readers of earlier drafts for encouragement and for valuable criticisms and suggestions.

Copyright © Roger Stokes 2005. This material may be freely reproduced, provided that this copyright notice, including this provision, is also reproduced.