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Foreword

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<h2 id="foreword">Foreword</h2>

Twenty years ago, in 1966, Kenneth E. Iverson and Adin Falkoff quietly introduced APL\360, the first interactive implementation of the programming language APL. Based on an earlier interpreter developed by Phil Abrams and Larry Breed while they were students at Stanford University, APL\360 was a time-shared implementation of the notation Iverson used in his book A Programming Language (Wiley, 1962). In fact, the name APL is derived from the initial letters of that book’s three word title.

After many implementations of and variations on APL from IBM and other companies, IBM released the program product APL2. APL2 generalizes and expands APL In three important areas: types of data permitted in an array; provision for a data item in an array to itself be an array; and treatment of operators.

APL2 allows an array to contain both numeric and character data, thus removing an early implementation restriction of APL. By permitting an item of an array to hold any other array, APL2 introduces nested arrays, enriching the data structures of the language. Finally, APL2 allows any function, either primitive or defined, to be the operand of an operator and, moreover, permits defined operators.

The end result of this generalization and expansion is a highly usable programming language. APL2 permits rapid development of applications and models of application design. It opens up a wealth of new programming paradigms that did not exist in APL.

This book introduces APL2 as a language in its own right. It does not assume that you know APL, and so does not compare and contrast the programming techniques of the two languages. With this book, you learn APL2 by concentrating on the data structures and programming techniques needed to solve problems using APL2. If you are familiar with APL, you may want to look at this book to get a feel for how APL2 differs from the APL you have come to know. You will be surprised to find that problems difficult to solve in APL are often simple in APL2.

The authors of this book are well acquainted with using, teaching, writing about, and implementing APL and APL2. From the latter days of APL\360 to the present, Jim Brown has been associated with the implementation and development of APL and APL2. He worked summers for the APL Design Group while he pursued his doctorate in Computer and Information Science (then Systems and Information Science) at Syracuse University. His dissertation, A Generalization of APL, supported by Trenchard More’s seminal work in array theory, forms the basis for APL2.

Sandra Pakin authored the APL\360 Reference Manual, and she co-authored with Ray Polivka the book APL: The Language and Its Usage and, with the staff of Computer Innovations, the book APL: A Short Course. Sandra Pakin was a major contributor to IBM’s APL2 Language Reference Manual. For many years, Ray Polivka has worked in IBM’s Mid-Hudson Education Center in Poughkeepsie, New York, where he has been a prime mover in shaping and teaching the IBM internal education courses in APL and APL2.

The authors have combined their APL2 experience and knowledge into a book that deserves more than a glance.

<div class="line-block">Garth Foster

Syracuse, New York

November 27, 1986<a href="#fn1" id="fnref1" role="doc-noteref">1</a></div>

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<li id="fn1" role="doc-endnote">Dr. Foster dated these introductory comments on the day that is now generally heralded as marking the twentieth birthday of APL.<a href="#fnref1" class="footnote-back" role="doc-backlink">↩︎</a></li>

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