Simula | Research & Encyclopedia Articles

Simula

Simula (as in "SIMUlation LAnguage") is based on the Algol60 programming language. It is highly standardized, allowing it to be portable between different computing platforms. Many important object-oriented concepts like classes, objects, abstract data types, and inheritance were introduced in Simula. Although Simula has never been widely used, the Smalltalk, C++, and Java programming languages have been influenced by Simula.

History

Simula was designed and built by Ole-Johan Dahl and Kristen Nygaard at the Norwegian Computing Centre in Oslo between 1962 and 1967. The first iteration of Simula is now referred to as Simula I. The first prototype of Simula I was implemented in 1964 for discrete event simulation, which, in essence, tells how to generate new values for variables and the times the new values should take effect. Simula I was geared toward problems in operations research, which is the study of quantitative (that is, statistical) methods like linear programming and simulation in the analysis and solving of organizational problems. Use of Simula I spread through Sweden, Germany, and the Soviet Union in the next few years.

During the 1960s, special-purpose programming languages were on the decline. Programming languages that could be used for multiple applications were becoming more popular. Simula was expanded and re-implemented as a general-purpose programming language in 1967. This version is referred to as Simula 67. The latest Simula language definition was adopted in 1986 and is maintained by the Simula Standards Group (SSG).

Programming in Simula

Simula is a procedural, block-structured language. Features of Simula include strong typing, procedures, conditional statements, repetitions, list processing, and file input/output functions. Simula's syntax and data types are similar to Algol. The basic data types include integer, real, Boolean, and character.

Programs consist of sequences of instructions called blocks. The simplest program may have only one block. Each block starts with the word begin and finishes with the word end. The block structure results in modularized programs. Within each block, programming instructions include declarations and statements. Declarations reserve and name memory locations for data types, and statements tell Simula what the program is to do. There are two basic types of statements: assignments and procedures. Assignments tell Simula to place a data value in a location specified by the declaration. Procedures are a sequence of steps or actions to be performed. Certain procedures are predefined by the system, and others can be defined within the program by the programmer.

Programmers create the source code in a text editor, compile the code through a Simula compiler, and link the resulting object code to any required run-time libraries. Most errors are detected during the compile process, but additional checking occurs when the program runs. Simula is not case-sensitive, meaning that programs can consist of any combination of upper-case and lower-case letters.