Simula

Simula is the name of two simulation programming languages, Simula I and Simula 67, developed in the 1960s at the Norwegian Computing Center in Oslo, by Ole-Johan Dahl and Kristen Nygaard. Syntactically, it is a fairly faithful superset of ALGOL 60,:1.3.1 also influenced by the design of Simscript. Simula is the name of two simulation programming languages, Simula I and Simula 67, developed in the 1960s at the Norwegian Computing Center in Oslo, by Ole-Johan Dahl and Kristen Nygaard. Syntactically, it is a fairly faithful superset of ALGOL 60,:1.3.1 also influenced by the design of Simscript. Simula 67 introduced objects,:2, 5.3 classes,:1.3.3, 2 inheritance and subclasses,:2.2.1 virtual procedures,:2.2.3 coroutines,:9.2 and discrete event simulation,:14.2 and features garbage collection.:9.1 Also other forms of subtyping (besides inheriting subclasses) were introduced in Simula derivatives. Simula is considered the first object-oriented programming language. As its name suggests, Simula was designed for doing simulations, and the needs of that domain provided the framework for many of the features of object-oriented languages today. Simula has been used in a wide range of applications such as simulating VLSI designs, process modeling, protocols, algorithms, and other applications such as typesetting, computer graphics, and education. The influence of Simula is often understated, and Simula-type objects are reimplemented in C++, Object Pascal, Java, C# and several other languages. Computer scientists such as Bjarne Stroustrup, creator of C++, and James Gosling, creator of Java, have acknowledged Simula as a major influence. The following account is based on Jan Rune Holmevik's historical essay. Kristen Nygaard started writing computer simulation programs in 1957. Nygaard saw a need for a better way to describe the heterogeneity and the operation of a system. To go further with his ideas on a formal computer language for describing a system, Nygaard realized that he needed someone with more computer programming skills than he had. Ole-Johan Dahl joined him on his work January 1962. The decision of linking the language up to ALGOL 60 was made shortly after. By May 1962 the main concepts for a simulation language were set. 'SIMULA I' was born, a special purpose programming language for simulating discrete event systems. Kristen Nygaard was invited to visit the Eckert–Mauchly Computer Corporation late May 1962 in connection with the marketing of their new UNIVAC 1107 computer. At that visit Nygaard presented the ideas of Simula to Robert Bemer, the director of systems programming at Univac. Bemer was a sworn ALGOL fan and found the Simula project compelling. Bemer was also chairing a session at the second international conference on information processing hosted by IFIP. He invited Nygaard, who presented the paper 'SIMULA -- An Extension of ALGOL to the Description of Discrete-Event Networks'. The Norwegian Computing Center got a UNIVAC 1107 August 1963 at a considerable discount, on which Dahl implemented the SIMULA I under contract with UNIVAC. The implementation was based on the UNIVAC ALGOL 60 compiler. SIMULA I was fully operational on the UNIVAC 1107 by January 1965. In the following couple of years Dahl and Nygaard spent a lot of time teaching Simula. Simula spread to several countries around the world and SIMULA I was later implemented on Burroughs B5500 computers and the Russian URAL-16 computer. In 1966 C. A. R. Hoare introduced the concept of record class construct, which Dahl and Nygaard extended with the concept of prefixing and other features to meet their requirements for a generalized process concept. Dahl and Nygaard presented their paper on Class and Subclass declarations at the IFIP Working Conference on simulation languages in Oslo, May 1967. This paper became the first formal definition of Simula 67. In June 1967 a conference was held to standardize the language and initiate a number of implementations. Dahl proposed to unify the type and the class concept. This led to serious discussions, and the proposal was rejected by the board. SIMULA 67 was formally standardized on the first meeting of the SIMULA Standards Group (SSG) in February 1968.