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BASIC interpreter

Interpreter that enables users to enter and run programs in the BASIC language

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BASIC interpreters are of historical importance. Microsoft's first product for sale was a BASIC interpreter (Altair BASIC), which paved the way for the company's success. Before Altair BASIC, microcomputers were sold as kits that needed to be programmed in machine code (for instance, the Apple I). During the Altair period, BASIC interpreters were sold separately, becoming the first software sold to individuals rather than to organizations; Apple BASIC was Apple's first software product. After the MITS Altair 8800, microcomputers were expected to ship bundled with BASIC interpreters of their own (e.g., the Apple II, which had multiple implementations of BASIC). A backlash against the price of Microsoft's Altair BASIC also led to early collaborative software development, for Tiny BASIC implementations in general and Palo Alto Tiny BASIC specifically.

BASIC interpreters fell from use as computers grew in power and their associated programs grew too long for typing them in to be a reasonable distribution format. Software increasingly came pre-compiled and transmitted on floppy disk or via bulletin board systems, making the need for source listings less important. Additionally, increasingly sophisticated command shells like MS-DOS and the Mac GUI became the primary user interface, and the need for BASIC to act as the shell disappeared. The use of BASIC interpreters as the primary language and interface to systems had largely disappeared by the mid-1980s.

History

BASIC helped jumpstart the time-sharing era, became mainstream in the microcomputer era, then faded to become just another application in the DOS and GUI era, and today survives in a few niches related to game development, retrocomputing, and teaching.

Time-sharing era

First implemented as a compile-and-go system rather than an interpreter, BASIC emerged as part of a wider movement towards time-sharing systems. General Electric, having worked on the Dartmouth Time-Sharing System and its associated Dartmouth BASIC, wrote their own underlying operating system and launched an online time-sharing system known as Mark I featuring a BASIC compiler (not an interpreter) as one of its primary selling points. Other companies in the emerging field quickly followed suit. By the early 1970s, BASIC was largely universal on general-purpose mainframe computers.

BASIC, as a streamlined language designed with integrated line editing in mind, was naturally suited to porting to the minicomputer market, which was emerging at the same time as the time-sharing services. These machines had very small main memory, perhaps as little as 4 KB in modern terminology, and lacked the high-performance storage like hard drives that make compilers practical. In contrast, an interpreter would take fewer computing resources, at the expense of performance. In 1968, Hewlett Packard introduced the HP 2000, a system that was based around its HP Time-Shared BASIC interpreter. In 1969, Dan Paymar and Ira Baxter wrote another early BASIC interpreter for the Data General Nova.

One holdout was Digital Equipment Corporation (DEC), the leading minicomputer vendor. They had released a new language known as FOCAL, based on the earlier JOSS developed on a DEC machine at the Stanford Research Institute in the early 1960s. JOSS was similar to BASIC in many respects, and FOCAL was a version designed to run in very small memory systems, notably the PDP-8, which often shipped with 4 KB of main memory. By the late 1960s, DEC salesmen, especially in the educational sales department, found that their potential customers were not interested in FOCAL and were looking elsewhere for their systems. This prompted David H. Ahl to hire a programmer to produce a BASIC for the PDP-8 and other DEC machines. Within the year, all interest in alternatives like JOSS and FOCAL had disappeared.

Microcomputer era

The introduction of the first microcomputers in the mid-1970s continued the explosive growth of BASIC, which had the advantage that it was fairly well known to the young designers and computer hobbyists who took an interest in microcomputers, many of whom had seen BASIC on minis or mainframes. BASIC was one of the few languages that was both high-level enough to be usable by those without training and small enough to fit into the microcomputers of the day. In 1972, HP introduced the HP 9830A programmable desktop calculator with a BASIC Plus interpreter in read-only memory (ROM).

In June 1974, Alfred Weaver, Michael Tindall, and Ronald Danielson of the University of Illinois at Urbana-Champaign proved it was possible to produce "A BASIC Language Interpreter for the Intel 8008 Microprocessor," in their paper of the same name, though their application was deployed to an 8008 simulator for the IBM 360/75 and required 16 KB.

In January 1975, the Altair 8800 was announced and sparked the microcomputer revolution. One of the first microcomputer versions of BASIC was co-written by Gates, Allen, and Monte Davidoff for their newly formed company, Micro-Soft. This was released by MITS in punch tape format for the Altair 8800 shortly after the machine itself, showcasing BASIC as the primary language for early microcomputers.

In March 1975, Steve Wozniak attended the first meeting of the Homebrew Computer Club and began formulating the design of his own computer. Club members were excited by Altair BASIC. Wozniak concluded that his machine would have to have a BASIC of its own. At the time he was working at Hewlett Packard and used their TS-BASIC minicomputer dialect as the basis for his own version. Integer BASIC was released on cassette for the Apple I, and was supplied in ROM when the Apple II shipped in the summer of 1977.

Other members of the Homebrew Computer Club began circulating copies of Altair BASIC on paper tape, causing Gates to write his Open Letter to Hobbyists, complaining about this early example of software piracy. Partially in response to Gate's letter, and partially to make an even smaller BASIC that would run usefully on 4 KB machines, Bob Albrecht urged Dennis Allison to write their own variation of the language. How to design and implement a stripped-down version of an interpreter for the BASIC language was covered in articles by Allison in the first three quarterly issues of the People's Computer Company newsletter published in 1975 and implementations with source code published in Dr. Dobb's Journal of Tiny BASIC Calisthenics & Orthodontia: Running Light Without Overbyte. This led to a wide variety of Tiny BASICs with added features or other improvements, with well-known versions from Tom Pittman and Li-Chen Wang, both members of the Homebrew Computer Club. Tiny BASIC was published openly and Wang coined the term "copyleft" to encourage others to copy his source code. Hobbyists and professionals created their own implementations, making Tiny BASIC an example of a free software project that existed before the free software movement.

Many firms developed BASIC interpreters. In 1976, SCELBI introduced SCELBAL for the 8008 and the University of Idaho and Lawrence Livermore Laboratory announced that they would be publishing to the public domain LLL BASIC, which included floating-point support. In 1977, the Apple II and TRS-80 Model I each had two versions of BASIC, a smaller version introduced with the initial releases of the machines and a licensed Microsoft version introduced later as interest in the platforms increased.

Microsoft ported its interpreter to the MOS 6502, which quickly became one of the most popular microprocessors of the 8-bit era. When new microcomputers began to appear, such as the Commodore PET, their manufacturers licensed a Microsoft BASIC, customized to the hardware capabilities. By 1978, MS BASIC was a de facto standard and practically every home computer of the 1980s included it in ROM. In 1980, as part of a larger licensing deal that included other languages and PC DOS, IBM rejected an overture from Atari and instead licensed MS-BASIC over its own implementation, eventually releasing four versions of IBM BASIC, each much larger than prior interpreters (for instance, Cartridge BASIC took 40 KB). Don Estridge, leader of the IBM PC team, said, "IBM has an excellent BASIC--it's well received, runs fast on mainframe computers, and it's a lot more functional than micro-computer BASICs... But [its] number of users were infinitesimal compared to the number of Microsoft BASIC users. Microsoft BASIC had hundreds of thousands of users around the world. How are you going to argue with that?" (See Microsoft BASIC for the subsequent history of these different implementations.)

Many vendors did "argue with that" and used other firms or wrote their own interpreters. In September 1978, Shepardson Microsystems was finishing Cromemco 16K Structured BASIC for the Z80-based Cromemco S-100 bus machines. Paul Laughton and Kathleen O'Brien then created Atari BASIC as essentially a pared-down version of Cromemco BASIC ported to the 6502. In 1979, Warren Robinett developed the BASIC Programming cartridge for Atari, Inc., even though it only supported programs with 9 lines of code (64 characters in total). Also in 1979, Texas Instruments released TI BASIC with its TI-99/4, which would sell nearly 3 million systems when revamped as the TI-99/4A. Sinclair BASIC was developed for the ZX-80 by John Grant and Steve Vickers of Nine Tiles. In 1980, Sophie Wilson of Acorn Computers developed Atom BASIC, which she later evolved into BBC BASIC, one of the first interpreters to offer structured BASIC programming, with named DEF PROC/DEF FN procedures and functions, REPEAT UNTIL loops, and IF THEN ELSE structures inspired by COMAL. Jan Jones developed SuperBASIC, another British BASIC supporting structured programming, for the Sinclair QL. In 1983, Randall Hyde developed SmartBASIC for the Coleco Adam. Richard Clayton, Chris Hall, and Paul Overell developed Mallard BASIC for the BBC Micro and Locomotive BASIC for the Amstrad CPC, both supporting commands for an ISAM indexed file system. In 1985, MetaComCo released ABasiC for the Amiga and ST BASIC for the Atari ST.

In 1978, David Lien published the first edition of The BASIC Handbook: An Encyclopedia of the BASIC Computer Language, documenting keywords across over 78 different computers. By 1981, the second edition documented keywords from over 250 different computers, showcasing the explosive growth of the microcomputer era.

Interpreters as applications

With the rise of disk operating systems and later graphical user interfaces, BASIC interpreters became just one application among many, rather than providing the first prompt a user might see when turning on a computer.

In 1983, the TRS-80 Model 100 portable computer debuted, with its Microsoft BASIC implementation noteworthy for two reasons. First, programs were edited using the simple text editor, TEXT, rather than typed in line by line (but line numbers were still required). Second, this was the last Microsoft product that Bill Gates developed personally.

Also in 1983, Microsoft began bundling GW-BASIC with DOS. Functionally identical to IBM BASICA, its BASIC interpreter was a fully self-contained executable and did not need the Cassette BASIC ROM found in the original IBM PC. According to Mark Jones Lorenzo, given the scope of the language, "GW-BASIC is arguably the ne plus ultra of Microsoft's family of line-numbered BASICs stretching back to the Altair--and perhaps even of line-numbered BASIC in general." With the release of MS-DOS 5.0, GW-BASIC's place was taken by QBasic.

MacBASIC featured a fully interactive development environment for the original Macintosh computer and was developed by Donn Denman, Marianne Hsiung, Larry Kenyon, and Bryan Stearns. MacBASIC was released as beta software in 1985 and was adopted for use in places such as the Dartmouth College computer science department, for use in an introductory programming course. It was doomed to be the second Apple-developed BASIC killed in favor of a Microsoft BASIC. In November 1985, Apple abruptly ended the project as part of a deal with Microsoft to extend the license for BASIC on the Apple II.

BASIC interpreters were not just an American/British development. In 1984, Hudson Soft released Family BASIC in the Japanese market for Nintendo's Family Computer video game console, an integer-only implementation designed for game programming, based on Hudson Soft BASIC for the Sharp MZ80 (with English keywords). Turbo-Basic XL is a compatible superset of Atari BASIC, developed by Frank Ostrowski and published in the December 1985 issue of German computer magazine Happy Computer, making it one of the last interpreters published as a type-in program. The language included a compiler in addition to the interpreter and featured structured programming commands. Several modified versions working with different DOS systems were released by other authors. In France, François Lionet and Constantin Sotiropoulos developed two BASIC interpreters with a focus on multimedia: STOS BASIC for the Atari ST, in 1988, and AMOS BASIC for the Amiga, in 1990.

In May 1991, Microsoft released Visual Basic, a third-generation event-driven programming language known for its Component Object Model (COM) programming model. Visual Basic supported the rapid application development (RAD) of graphical user interface (GUI) applications, access to databases using Data Access Objects, Remote Data Objects, or ActiveX Data Objects, and creation of ActiveX controls and objects. Visual Basic was used to develop proprietary in-house applications as well as published applications.

Niche BASICs

In 1993, Microsoft released Visual Basic for Applications, a scripting language for Microsoft Office applications, which supersedes and expands on the abilities of earlier application-specific macro programming languages such as Word's WordBASIC (which had been introduced in 1989).

In 1996, Microsoft released VBScript as an alternative to JavaScript for adding interactive client-side functionality to web pages viewed with Internet Explorer.

In 1999, Benoît Minisini released Gambas as an alternative for Visual Basic developers who had decided to migrate to Linux.

In 2000, Lee Bamber and Richard Vanner released DarkBASIC, a game creation system for Microsoft Windows, with accompanying integrated development environment (IDE) and development tools.

In 2001, SmallBASIC was released for the Palm PDA. Another BASIC interpreter for Palm was HotPaw BASIC, an offshoot of Chipmunk Basic.

In 2002, Emmanuel Chailloux, Pascal Manoury and Bruno Pagano published a Tiny BASIC as an example of developing applications with Objective Caml (OCaml).

In 2011, Microsoft released Small Basic (distinct from SmallBASIC), together with a teaching curriculum and an introductory guide., designed to help students who have learnt visual programming languages such as Scratch learn text-based programming. The associated IDE provides a simplified programming environment with functionality such as syntax highlighting, intelligent code completion, and in-editor documentation access. The language has only 14 keywords. In 2019, Microsoft announced Small Basic Online (SBO), allowing students to run programs from a web browser.

In 2014, Robin H. Edwards released Arduino BASIC for the Arduino, and now a widely forked implementation. Another implementation using the same name was adapted from Palo Alto Tiny BASIC in 1984 by Gordon Brandly for his 68000 Tiny BASIC, later ported to C by Mike Field.

Many BASIC interpreters are now available for smartphones and tablets via the Apple App Store, or Google Play store for Android.

Today, coding BASIC interpreters has become part of the retrocomputing hobby. Higher level programming languages on systems with extensive RAM have simplified implementing BASIC interpreters. For instance, line management is simple if an implementation language supports sparse matrixes, variable management is simple with associative arrays, and program execution is easy with eval functions. As examples, see the open source project Vintage BASIC, written in Haskell or OCaml Tiny BASIC.

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