APL (programming Language) - History

History

The first incarnation of what was later to be the APL programming language was published and formalized in A Programming Language, a book describing a notation invented in 1957 by Kenneth E. Iverson while at Harvard University. Iverson had developed a mathematical notation for manipulating arrays that he taught to his students.

In 1960, he began work for IBM and, working with Adin Falkoff, created APL based on the notation he had developed. This notation was used inside IBM for short research reports on computer systems, such as the Burroughs B5000 and its stack mechanism when stack machines versus register machines were being evaluated by IBM for upcoming computers.

Also in 1960, Iverson was already also using his notation in a draft copy of Chapter 6 called "A programming language" for the book he was writing with Fred Brooks, Automatic Data Processing, which would later be published in 1963.

Published in 1962, the notation described in A Programming Language was recognizable yet distinct from later APL.

As early as 1962, the first attempt to use the notation to describe a complete computer system happened after Falkoff discussed with Dr. William C. Carter his work in the standardization of the instruction set for the machines that later became the IBM System/360 family.

In 1963, Dr. Herbert Hellerman, working at the IBM Systems Research Institute, implemented a part of the notation on an IBM 1620 computer, and it was used by students in a special high school course on calculating transcendental functions by series summation. Students tested their code in Dr. Hellerman's lab. This implementation of a portion of the notation was called PAT (Personalized Array Translator).

In 1963, Falkoff, Iverson, and Edward H. Sussenguth Jr., all working at IBM, used the notation for a formal description of the IBM System/360 series machine architecture and functionality, which resulted in a paper published in IBM Systems Journal in 1964. After this was published, the team turned their attention to an implementation of the notation on a computer system. One of the motivations for this focus of implementation was the interest of John L. Lawrence who had new duties with Science Research Associates, an educational company bought by IBM in 1964. Lawrence asked Iverson and his group to help utilize the language as a tool for the development and use of computers in education.

After Lawrence M. Breed and Philip S. Abrams of Stanford University joined the team at IBM Research, they continued their prior work on an implementation programmed in FORTRAN IV for a portion of the notation was done for the IBM 7090 computer running under the IBSYS operating system. This work was finished in late 1965 and later known as IVSYS (Iverson System). The basis of this implementation was described in detail by Abrams in a Stanford University Technical Report, "An Interpreter for Iverson Notation" in 1966. Like Hellerman's PAT system earlier, this implementation did not include the APL character set but used special English reserved words for functions and operators. The system was later adapted for a time-sharing system and, by November 1966, it had been reprogrammed for the IBM/360 Model 50 computer running in a time sharing mode and was used internally at IBM.

A key development in the ability to use APL effectively, before the widespread use of CRT terminals, was the development of a special IBM Selectric typewriter interchangeable typeball with all the special APL characters on it. This was used on paper printing terminal workstations using the Selectric typewriter and typeball mechanism, such as the IBM 1050 and IBM 2741 terminal. Keycaps could be placed over the normal keys to show which APL characters would be entered and typed when that key was struck. For the first time, a programmer could actually type in and see real APL characters as used in Iverson's notation and not be forced to use awkward English keyword representations of them. Falkoff and Iverson had the special APL Selectric typeballs, 987 and 988, designed in late 1964, although no APL computer system was available to use them. Iverson cited Falkoff as the inspiration for the idea of using an IBM Selectric typeball for the APL character set.

The IBM 2741 keyboard layout with the APL typeball print head inserted looked this way to the programmer:

Some APL symbols, even with the APL characters on the typeball, still had to be typed in by over-striking two existing typeball characters. An example would be the "grade up" character, which had to be made from a "delta" (shift-H) and a "Sheffer stroke" (shift-M). This was necessary because the APL character set was larger than the 88 characters allowed on the Selectric typeball.

The first APL interactive login and creation of an APL workspace was in 1966 by Larry Breed using a 1050 terminal at the IBM Mohansic Labs near Thomas J. Watson Research Center, the home of APL, in Yorktown Heights, New York.

IBM was chiefly responsible for the introduction of APL to the marketplace.

APL was first available in 1967 for the IBM 1130 as APL\1130. It would run in as little as 8k 16 bit words of memory, and used a dedicated 1 megabyte hard disk.

APL gained its foothold on mainframe timesharing systems from the late 1960s through the early 1980s, in part because it would run on lower-specification systems that were not equipped with Dynamic Address Translation hardware. Additional improvements in performance for selected IBM System/370 mainframe systems included the "APL Assist Microcode" in which some support for APL execution was included in the actual firmware as opposed to APL being exclusively a software product. Somewhat later, as suitably performing hardware was finally becoming available in the mid to late-1980s, many users migrated their applications to the personal computer environment.

Early IBM APL interpreters for IBM 360 and IBM 370 hardware implemented their own multi-user management instead of relying on the host services, thus they were timesharing systems in their own right. First introduced in 1966, the APL\360 system was a multi-user interpreter. The ability to programmatically communicate with the operating system for information and setting interpreter system variables was done through special privileged "I-beam" functions, using both monadic and dyadic operations.

In 1973, IBM released APL.SV, which was a continuation of the same product, but which offered shared variables as a means to access facilities outside of the APL system, such as operating system files. In the mid-1970s, the IBM mainframe interpreter was even adapted for use on the IBM 5100 desktop computer, which had a small CRT and an APL keyboard, when most other small computers of the time only offered BASIC. In the 1980s, the VSAPL program product enjoyed widespread usage with CMS, TSO, VSPC, MUSIC/SP and CICS users.

In 1973-1974, Dr. Patrick E. Hagerty directed the implementation of the University of Maryland APL interpreter for the Sperry Univac 1100 Series mainframe computers. At the time, Sperry had nothing. In 1974, student Alan Stebbens was assigned the task of implementing an internal function. And student Bill Linton caused massive dumps to occur as he practiced developing APL programs in the third-floor TTY room, causing Dr. Hagerty to burst through the TTY door to halt the practice until Dr. Hagerty fixed the APL interpreter bug.

Several timesharing firms sprang up in the 1960s and 1970s that sold APL services using modified versions of the IBM APL\360 interpreter. In North America, the better-known ones were I. P. Sharp Associates, Scientific Time Sharing Corporation, and The Computer Company (TCC). With the advent first of less expensive mainframes such as the IBM 4300 and later the personal computer, the timesharing industry had all but disappeared by the mid-1980s.

Sharp APL was available from I. P. Sharp Associates, first on a timesharing basis in the 1960s, and later as a program product starting around 1979. Sharp APL was an advanced APL implementation with many language extensions, such as packages (the ability to put one or more objects into a single variable), file system, nested arrays, and shared variables.

APL interpreters were available from other mainframe and mini-computer manufacturers as well, notably Burroughs, CDC, Data General, DEC, Harris, Hewlett-Packard, Siemens, Xerox, and others.

Garth Foster of Syracuse University sponsored regular meetings of the APL implementers' community at Syracuse's Minnowbrook Conference Center in rural upstate New York. In later years, Eugene McDonnell organized similar meetings at the Asilomar Conference Grounds near Monterey, California, and at Pajaro Dunes near Watsonville, California. The SIGAPL special interest group of the Association for Computing Machinery continues to support the APL community.

In 1979, Iverson received the Turing Award for his work on APL.