| • Science | • People | • Locations | • Timeline |
There were three main official versions of ALGOL: ALGOL 58, ALGOL 60, and ALGOL 68. Of these, ALGOL 60 was the most widely known in the United States. ( Niklaus Wirth based his own Algol-W on ALGOL 60, before moving to develop Pascal.) The official ALGOL versions are named after the year they were published. ALGOL 58 was originally known as the IAL (for International Algorithmic Language.)
Note: throughout its effective life, the name of the programming language ALGOL was always presented in all-uppercase letters, and this is the practice we've adopted here.
ALGOL was developed jointly by a committee of European and American computer scientists. It specified three different syntaxes: a reference syntax, a publication syntax, and an implementation syntax. The different syntaxes permitted it to use different keyword names and conventions for decimal points (commas vs. periods) for different languages.
John Backus developed the Backus normal form method of describing programming languages specifically for ALGOL 58. It was revised and expanded by Peter Naur to the Backus-Naur formThe Backus-Naur form BNF (also known as Backus normal form is a metasyntax used to express context-free grammars: that is, a formal way to describe formal languages. BNF is widely used as a notation for the grammars of computer programming languages, comm for ALGOL 60. Both John Backus and Peter Naur served on the committee which created ALGOL 60. ALGOL 60 inspired many languages that followed it; the canonical quote in this regard is C. A. R. HoareSir Charles Antony Richard Hoare Tony Hoare is a British computer scientist, probably best known for the development of Quicksort, the world's most widely used sorting algorithm, and perhaps even the world's most widely used algorithm of any kind, in 1960's "ALGOL was a great improvement on its successors." The full quote is "Here is a language so far ahead of its time, that it was not only an improvement on its predecessors, but also on nearly all its successors", but the aphoristic version is far better known. It is sometimes erroneously attributed to Edsger DijkstraEdsger Wybe Dijkstra ( Rotterdam, May 11, 1930 Nuenen, August 6, 2002) was a Dutch computer scientist. Dijkstra studied theoretical physics at the University of Leiden. He worked as a research fellow for Burroughs Corporation in the early 1970s. He worked, also known for his pointed comments, who helped to implement the first ALGOL 60 compilerA compiler is a computer program that translates a computer program written in one computer language (called the source language into an equivalent program written in another computer language (called the output or the target language . Introduction and h.The Burroughs Corporation's B5000 and its successors were stack machineIn computer science, a stack machine is a model of computation in which the computer's memory takes the form of a stack. The term also refers to an actual computer implementing or simulating the idealized stack machine. In computability theory, the pushdos designed to be programmed in an extended variant of ALGOL 60, known as Elliot ALGOL; indeed their operating system, or MCP (Master Control Program) as they are called, was written in Elliot ALGOL as far back as 1961. The Unisys Corporation still markets machines descended from the B5000 today, running the MCP and supporting a diverse set of Elliot ALGOL compilers.
ALGOL 60 as officially defined had no I/O facilities; implementations necessarily had to add some, but they varied from one implementation to another. In contrast, ALGOL 68 offered an extensive library of transput (ALGOL 68 parlance for Input/Output) facilities.
ALGOL 60 allowed for two types of parameter passing: the common call-by-value, and the unique call-by-name, which has never again been adopted by any of its successor languages. Call-by-name had certain limitations in contrast to call-by-reference, making it an undesirable feature in language design. For example, it is impossible in ALGOL 60 to develop a procedure that will swap the values of two parameters if the actual parameters that are passed in are an integer variable and an array that is indexed by that same integer variable.
ALGOL 68 was defined using a two-level grammar formalism invented by Adriaan van Wijngaarden and which bears his name. Van Wijngaarden grammars use a context-free grammar to generate an infinite set of productions that will recognize a particular ALGOL 68 program; notably, they are able to express the kind of requirements that in many other programming language standards are labelled "semantics" and have to be expressed in ambiguity-prone natural language prose, and then implemented in compilers as ad hoc code attached to the formal language parser.