Atlas Autocode (AA) was a programming language developed at Manchester University for the Atlas Computer. It was developed by Tony Brooker as an improvement on the ALGOL programming languages, removing some of Algol's poorer features such as passing parameters by name. It featured explicitly typed variables, subroutines and functions. The AA compiler generated range-checking for array accesses, and the language allowed an array to have dimensions that were determined at run-time (i.e. you could declare an array as %integer %array Thing (i:j), where i and j were calculated values). Atlas Autocode included a "%complex" data type which would support imaginary numbers (eg the square root of -1), a feature which was dropped when the language later morphed into the Edinburgh IMP programming language. (Imp was an extension of AA and was notable for being used to write the EMAS operating system.) A programming language or computer language is a standardized communication technique for expressing instructions to a computer. ... The Atlas Computer of the University of Manchester became operational in 1962, having been a joint development between the University, Ferranti and Plessey. ... The position of Algol Algol (β Per / Beta Persei) is a bright star in the constellation Perseus. ... A programming language or computer language is a standardized communication technique for expressing instructions to a computer. ... Edinburgh IMP is a development of ATLAS Autocode, initially developed around 1966-1969 at Edinburgh University, Scotland. ... The Edinburgh Multi-Access System (EMAS) was an operating system developed at the University of Edinburgh, Scotland, during the 1970s. ... In computing, an operating system (OS) is the system software responsible for the direct control and management of hardware and basic system operations. ...

Keywords in AA were represented as being underlined, however for the sake of easy typing it was possible to strop keywords by placing a "%" sign in front of them. There were no reserved words in the language. For example "%if token=if %then %result = token" refers to a variable called "if".

Because of this keyword stropping, it was possible for AA to allow spaces in variable names, such as "%integer previous value". Spaces were not significant and were removed prior to parsing.

The syntax for expressions was very close to mathematical standards and allowed implicit multiplication such as "z = 3x + y" as an alternative to the more common "z = x * 3 + y".

Atlas Autocode's syntax was influenced by the output device which the author had available, a Flexowriter. Consequently it allowed symbols like "" and superscripts for "i²". The flexowriter supported overstriking and therefore AA did as well - up to three characters could be overstruck as a single symbol. For example the character set had no "^" symbol, so exponentiation was an overstrike of "|" and "*". (The underlining of keywords mentioned above could also be done using overstriking.) The language is described in detail in the Atlas Autocode Reference Manual.

When AA was ported to the KDF9 computer, the character set was changed to ISO and that compiler has actually been recovered from an old paper tape by the Edinburgh Computer History Project and is available online, as is a high-quality scan of the original Atlas Autocode manual. KDF9 was an early British computer designed and built by English Electric, later English Electric Leo Marconi, EELM, later still incorporated into ICL. It came into service ca. ...

Atlas Autocode's second-greatest claim to fame (after being the progenitor of Imp and EMAS) was that it was the original "Compiler Compiler" of which "Yacc" was a later derivative. A variant of the AA compiler included run-time support for a top-down recursive descent parser. The style of parser used in the Compiler Compiler was in use continuously at Edinburgh from the 60's until almost the turn of the millennium. A compiler-compiler or parser generator is a utility for generating the source code of a parser, interpreter or compiler from an annotated language description in the form of a grammar (usually in BNF) plus code that is associated with each of the rules of the grammar that should be... Yacc is a piece of computer software that serves as the standard parser generator on Unix systems. ...

Other Autocodes were developed for the Titan (computer) (a prototype Atlas 2) at Cambridge and the Ferranti Mercury. Autocode is a class of simple high-level programming languages devised for a series of machines at the Universities of Manchester and Cambridge. ... The Titan computer was the name given to the Atlas 2 developed by Ferranti and the University of Cambridge Mathematical Laboratory. ... Ferranti or Ferranti International Signal plc by the time of its collapse, was a major UK electrical engineering and equipment firm, known primarily for their defense electronics and power grid systems. ...