ABC (programming language)

ABC is an imperative general-purpose programming language and integrated development environment (IDE) developed at Centrum Wiskunde & Informatica (CWI), in Amsterdam, Netherlands by Leo Geurts, Lambert Meertens, and Steven Pemberton.^[2] It is interactive, structured, high-level, and intended to be used instead of BASIC, Pascal, or AWK. It is intended for teaching or prototyping, but not as a systems-programming language.

ABC
Paradigms	multi-paradigm: imperative, procedural, structured
Designed by	Leo Geurts, Lambert Meertens, Steven Pemberton
Developer	Centrum Wiskunde & Informatica (CWI)
First appeared	January 1987; 38 years ago (1987-01)
Stable release	1.05.02 / 1990; 35 years ago (1990)
Typing discipline	strong, polymorphic
OS	Unix-like, Windows, MacOS, and Atari TOS
Website	homepages.cwi.nl/~steven/abc/
Influenced by
SETL, ALGOL 68[1]
Influenced
Python

ABC had a major influence on the design of the language Python, developed by Guido van Rossum, who formerly worked for several years on the ABC system in the mid-1980s.^[3][4]

Features

Its designers claim that ABC programs are typically around a quarter the size of the equivalent Pascal or C programs, and more readable.^[5] Key features include:

• Only five basic data types
• No required variable declarations
• Explicit support for top-down programming
• Statement nesting is indicated by indentation, via the off-side rule
• Infinite precision arithmetic, unlimited-sized lists and strings, and other features supporting orthogonality and ease of use by novices
• Polymorphic commands and functions
• Interactive environment with command completion, persistent workspaces, and no separate file handling

ABC was originally a monolithic implementation, leading to an inability to adapt to new requirements, such as creating a graphical user interface (GUI). ABC could not directly access the underlying file system and operating system.

The full ABC system includes a programming environment with a structure editor (syntax-directed editor), suggestions, static variables (persistent), and multiple workspaces, and is available as an interpreter–compiler. As of 2020^[update], the latest version is 1.05.02, for Unix, MS-DOS, Atari ST, and MacOS.

Example

An example function to collect the set of all words in a document:^[6]

HOW TO RETURN words document:
   PUT {} IN collection
   FOR line IN document:
      FOR word IN split line:
         IF word not.in collection:
            INSERT word IN collection
   RETURN collection

Implementations

ABC has been through multiple iterations, with the current version being the 4th major release. Implementations exist for Unix-like systems, MS-DOS/Windows, Macintosh, and other platforms. The source code was made available via Usenet in the late 1980s/early 1990s.