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ALGOL (short for ALGOrithmic Language) is a family of imperative computer programming languages originally developed in the mid 1950s which greatly influenced many other languages, and became the de facto way algorithms were described in text-books and academic works for almost the next 30 years. It was designed to avoid some of the perceived problems with FORTRAN and eventually gave rise to many other programming languages (including Pascal). ALGOL uses bracketed statement blocks and was the first language to use begin end pairs for delimiting them. Fragments of ALGOL-like syntax are sometimes still used as a notation for algorithms, so-called Pidgin Algol. ALGOL 58ALGOL 58 is the first language in the ALGOL programming language family. It was an early compromise design soon superseded by ALGOL 60; ALGOL 58 introduced the fundamental notion of compound statement, but it was restricted to control flow only, and it was not tied to identifier scope. The language was originally proposed to be called IAL (International Algebraic Language), but at a meeting in Zürich in May 1958, IAL was rejected as an "'unspeakable' and pompous acronym" (Perlis, 1981), and ALGOL suggested instead, though not officially adopted until a year later. Unresolved disagreements also led to a plan to define two dialects, ALGOL 58 and ALGOL 60. ALGOL 58 saw some implementation effort at IBM, but the effort was in competition with FORTRAN, and soon abandoned. It was also implemented at Dartmouth College on an LGP-30 but that implementation soon evolved into Algol 60. An implementation for the Burroughs 220 called BALGOL evolved along its own lines as well, but retained much of ALGOL 58's original character. ALGOL 58's primary contribution was to later languages; it was used as a basis for JOVIAL, MAD, NELIAC and ALGO. It was also used during 1959 to publish algorithms in CACM, beginning a trend of using ALGOL notation in publication that continued for many years. ALGOL 60John 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 form for ALGOL 60. Both John Backus and Peter Naur served on the committee which created ALGOL 60, as did Wally Feurzeig who later created Logo. ALGOL 60 inspired many languages that followed it; the canonical quote in this regard is C.A.R. Hoare's "ALGOL 60 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 Dijkstra, also known for his pointed comments, who helped to implement an early ALGOL 60 compiler. (This statement was in part a criticism of the bloatedness of ALGOL 68.) The Burroughs Corporation's B5000 and its successors were stack machines designed to be programmed in an extended variant of ALGOL 60, known as Elliott ALGOL; indeed their operating system the MCP, was written in Elliott 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 Elliott ALGOL compilers. Another early implementation was Dartmouth ALGOL 30 on the LGP-30 computer. 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 evaluation strategies for parameter passing: the common call-by-value, and call-by-name. 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. However, call-by-name is still beloved of ALGOL implementors for the interesting "thunks" that are used to implement it. ALGOL 68ALGOL 68 was defined using a two-level grammar formalism invented by Adriaan van Wijngaarden. 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. The main principles of design are completeness and clarity of design, orthogonal design, security, efficiency, the latter by static mode checking, mode-independent parsing, independent compilation and loop optimization. Critics of ALGOL 68, prominently C. A. R. Hoare, point out that it abandoned the simplicity of ALGOL 60 and became a vehicle for various complex ideas of its designers. The language also did little to make the compiler writer's task easy, in contrast to deliberately simple contemporaries (and competitors) C, S-algol and Pascal. Though European defence agencies (in Britain Royal Signals and Radar Establishment - RRSE) promoted the use of ALGOL 68 for its expected security advantages, the American side of the NATO alliance decided to develop a different project, the Ada programming language. The use of Ada was made obligatory for defence contracts. Apparently there was no room for two languages of similar application range in the NATO. Perhaps the acceptance of ALGOL 68 on the Russian side, then Soviet Union, was not helpful on this, either. The ALGOL 68 heritage is acknowledged by Scheme, and by C++. Article source: http://en.wikipedia.org/wiki/ALGOL, http://www.computernostalgia.net/articles/algol58.htm, http://www.computernostalgia.net/articles/algol60.htm, and http://www.computernostalgia.net/articles/algol68.htm Go back to Programming and Web Development Articles home page
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