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ALGOL (; short for "Algorithmic Language") is a family of imperative computer programming languages originally developed in 1958. ALGOL heavily influenced many other languages and was the standard method for
algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...
description used by the
Association for Computing Machinery The Association for Computing Machinery (ACM) is a US-based international learned society for computing. It was founded in 1947 and is the world's largest scientific and educational computing society. The ACM is a non-profit professional membe ...
(ACM) in textbooks and academic sources for more than thirty years. In the sense that the syntax of most modern languages is "Algol-like", it was arguably more influential than three other high-level programming languages among which it was roughly contemporary: FORTRAN, Lisp, and
COBOL COBOL (; an acronym for "common business-oriented language") is a compiled English-like computer programming language designed for business use. It is an imperative, procedural and, since 2002, object-oriented language. COBOL is primarily us ...
. It was designed to avoid some of the perceived problems with FORTRAN and eventually gave rise to many other programming languages, including
PL/I PL/I (Programming Language One, pronounced and sometimes written PL/1) is a procedural, imperative computer programming language developed and published by IBM. It is designed for scientific, engineering, business and system programming. I ...
, Simula,
BCPL BCPL ("Basic Combined Programming Language") is a procedural, imperative, and structured programming language. Originally intended for writing compilers for other languages, BCPL is no longer in common use. However, its influence is still ...
, B,
Pascal Pascal, Pascal's or PASCAL may refer to: People and fictional characters * Pascal (given name), including a list of people with the name * Pascal (surname), including a list of people and fictional characters with the name ** Blaise Pascal, Frenc ...
, and C. ALGOL introduced code blocks and the begin...end pairs for delimiting them. It was also the first language implementing nested function definitions with
lexical scope In computer programming, the scope of a name binding (an association of a name to an entity, such as a variable) is the part of a program where the name binding is valid; that is, where the name can be used to refer to the entity. In other part ...
. Moreover, it was the first programming language which gave detailed attention to formal language definition and through the '' Algol 60 Report'' introduced
Backus–Naur form In computer science, Backus–Naur form () or Backus normal form (BNF) is a metasyntax notation for context-free grammars, often used to describe the syntax of languages used in computing, such as computer programming languages, document formats ...
, a principal
formal grammar In formal language theory, a grammar (when the context is not given, often called a formal grammar for clarity) describes how to form strings from a language's alphabet that are valid according to the language's syntax. A grammar does not describe ...
notation for language design. There were three major specifications, named after the years they were first published: *
ALGOL 58 ALGOL 58, originally named IAL, is one of the family of ALGOL computer programming languages. It was an early compromise design soon superseded by ALGOL 60. According to John Backus The Zurich ACM-GAMM Conference had two principal motives in prop ...
– originally proposed to be called ''IAL'', for ''International Algebraic Language''. *
ALGOL 60 ALGOL 60 (short for ''Algorithmic Language 1960'') is a member of the ALGOL family of computer programming languages. It followed on from ALGOL 58 which had introduced code blocks and the begin and end pairs for delimiting them, representing a ...
– first implemented as ''X1 ALGOL 60'' in 1961. Revised 1963. *
ALGOL 68 ALGOL 68 (short for ''Algorithmic Language 1968'') is an imperative programming language that was conceived as a successor to the ALGOL 60 programming language, designed with the goal of a much wider scope of application and more rigorously de ...
– introduced new elements including flexible arrays, slices, parallelism, operator identification. Revised 1973. ALGOL 68 is substantially different from ALGOL 60 and was not well received, so in general "Algol" means ALGOL 60 and its dialects.


History

ALGOL was developed jointly by a committee of European and American computer scientists in a meeting in 1958 at the Swiss Federal Institute of Technology in Zurich (cf.
ALGOL 58 ALGOL 58, originally named IAL, is one of the family of ALGOL computer programming languages. It was an early compromise design soon superseded by ALGOL 60. According to John Backus The Zurich ACM-GAMM Conference had two principal motives in prop ...
). 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. ALGOL was used mostly by research computer scientists in the United States and in Europe. Its use in commercial applications was hindered by the absence of standard input/output facilities in its description and the lack of interest in the language by large computer vendors other than
Burroughs Corporation The Burroughs Corporation was a major American manufacturer of business equipment. The company was founded in 1886 as the American Arithmometer Company. In 1986, it merged with Sperry UNIVAC to form Unisys. The company's history paralleled many ...
. ALGOL 60 did however become the standard for the publication of algorithms and had a profound effect on future language development. John Backus developed the ''Backus normal form'' method of describing programming languages specifically for ALGOL 58. It was revised and expanded by
Peter Naur Peter Naur (25 October 1928 – 3 January 2016) was a Danish computer science pioneer and Turing award winner. He is best remembered as a contributor, with John Backus, to the Backus–Naur form (BNF) notation used in describing the syntax for mo ...
for ALGOL 60, and at Donald Knuth's suggestion renamed
Backus–Naur form In computer science, Backus–Naur form () or Backus normal form (BNF) is a metasyntax notation for context-free grammars, often used to describe the syntax of languages used in computing, such as computer programming languages, document formats ...
. Peter Naur: "As editor of the ALGOL Bulletin I was drawn into the international discussions of the language and was selected to be member of the European language design group in November 1959. In this capacity I was the editor of the ALGOL 60 report, produced as the result of the ALGOL 60 meeting in Paris in January 1960."ACM Award Citation: Peter Naur
, 2005
The following people attended the meeting in Paris (from 1 to 16 January): *
Friedrich L. Bauer Friedrich Ludwig "Fritz" Bauer (10 June 1924 – 26 March 2015) was a German pioneer of computer science and professor at the Technical University of Munich. Life Bauer earned his Abitur in 1942 and served in the Wehrmacht during World Wa ...
,
Peter Naur Peter Naur (25 October 1928 – 3 January 2016) was a Danish computer science pioneer and Turing award winner. He is best remembered as a contributor, with John Backus, to the Backus–Naur form (BNF) notation used in describing the syntax for mo ...
,
Heinz Rutishauser Heinz Rutishauser (30 January 1918 – 10 November 1970) was a Swiss mathematician and a pioneer of modern numerical mathematics and computer science. Life Rutishauser's father died when he was 13 years old and his mother died three years lat ...
,
Klaus Samelson Klaus Samelson (21 December 1918 – 25 May 1980) was a German mathematician, physicist, and computer pioneer in the area of programming language translation and push-pop stack algorithms for sequential formula translation on computers. Early ...
, Bernard Vauquois,
Adriaan van Wijngaarden Adriaan "Aad" van Wijngaarden (2 November 1916 – 7 February 1987) was a Dutch mathematician and computer scientist. Trained as an engineer, Van Wijngaarden would emphasize and promote the mathematical aspects of computing, first in numerical an ...
, and Michael Woodger (from Europe) * John W. Backus,
Julien Green Julien Green (September 6, 1900 – August 13, 1998) was an American writer who authored several novels (''The Dark Journey'', ''The Closed Garden'', ''Moira'', ''Each Man in His Darkness'', the ''Dixie'' trilogy, etc.), a four-volume autobiog ...
,
Charles Katz Charles Katz (born in 1927) is an American mathematician and computer scientist known for his contributions to early compiler development in the 1950s. He received two degrees in mathematics, a Bachelor of Science (B.S.) at Temple University i ...
, John McCarthy,
Alan J. Perlis Alan Jay Perlis (April 1, 1922 – February 7, 1990) was an American computer scientist and professor at Purdue University, Carnegie Mellon University and Yale University. He is best known for his pioneering work in programming languages and was t ...
, and
Joseph Henry Wegstein Joseph Henry Wegstein (April 7, 1922 in Washburn, Illinois - August 16, 1985) was an American computer scientist. Wegstein attended the University of Illinois, where he earned a Bachelor of Science (B.S.) degree in physics in 1944, and graduated ...
(from the USA). Alan Perlis gave a vivid description of the meeting: "The meetings were exhausting, interminable, and exhilarating. One became aggravated when one's good ideas were discarded along with the bad ones of others. Nevertheless, diligence persisted during the entire period. The chemistry of the 13 was excellent." ALGOL 60 inspired many languages that followed it. Tony Hoare remarked: "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." The
Scheme A scheme is a systematic plan for the implementation of a certain idea. Scheme or schemer may refer to: Arts and entertainment * ''The Scheme'' (TV series), a BBC Scotland documentary series * The Scheme (band), an English pop band * ''The Schem ...
programming language, a variant of Lisp that adopted the block structure and lexical scope of ALGOL, also adopted the wording "Revised Report on the Algorithmic Language Scheme" for its standards documents in homage to ALGOL.


ALGOL and programming language research

As Peter Landin noted, ALGOL was the first language to combine seamlessly imperative effects with the (
call-by-name In a programming language, an evaluation strategy is a set of rules for evaluating expressions. The term is often used to refer to the more specific notion of a ''parameter-passing strategy'' that defines the kind of value that is passed to the f ...
) lambda calculus. Perhaps the most elegant formulation of the language is due to
John C. Reynolds John Charles Reynolds (June 1, 1935 – April 28, 2013) was an American computer scientist. Education and affiliations John Reynolds studied at Purdue University and then earned a Doctor of Philosophy (Ph.D.) in theoretical physics from Harvard U ...
, and it best exhibits its syntactic and semantic purity. Reynolds's idealized ALGOL also made a convincing methodologic argument regarding the suitability of local effects in the context of call-by-name languages, in contrast with the global effects used by
call-by-value In a programming language, an evaluation strategy is a set of rules for evaluating expressions. The term is often used to refer to the more specific notion of a ''parameter-passing strategy'' that defines the kind of value that is passed to the f ...
languages such as ML. The conceptual integrity of the language made it one of the main objects of semantic research, along with
Programming Computable Functions In computer science, Programming Computable Functions (PCF) is a typed functional language introduced by Gordon Plotkin in 1977, based on previous unpublished material by Dana Scott. It can be considered to be an extended version of the typed lam ...
(PCF) and ML.


IAL implementations timeline

To date there have been at least 70 augmentations, extensions, derivations and sublanguages of Algol 60. The Burroughs dialects included special Bootstrapping dialects such as ESPOL and NEWP. The latter is still used for Unisys MCP system software.


Properties

ALGOL 60 as officially defined had no I/O facilities; implementations defined their own in ways that were rarely compatible with each other. In contrast, ALGOL 68 offered an extensive library of ''transput'' (input/output) facilities. ALGOL 60 allowed for two evaluation strategies for parameter passing: the common
call-by-value In a programming language, an evaluation strategy is a set of rules for evaluating expressions. The term is often used to refer to the more specific notion of a ''parameter-passing strategy'' that defines the kind of value that is passed to the f ...
, and
call-by-name In a programming language, an evaluation strategy is a set of rules for evaluating expressions. The term is often used to refer to the more specific notion of a ''parameter-passing strategy'' that defines the kind of value that is passed to the f ...
. Call-by-name has certain effects in contrast to
call-by-reference In a programming language, an evaluation strategy is a set of rules for evaluating expressions. The term is often used to refer to the more specific notion of a ''parameter-passing strategy'' that defines the kind of value that is passed to the f ...
. For example, without specifying the parameters as ''value'' or ''reference'', it is impossible 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. Think of passing a pointer to swap(i, A in to a function. Now that every time swap is referenced, it is reevaluated. Say i := 1 and A := 2, so every time swap is referenced it will return the other combination of the values ( ,2 ,1 ,2and so on). A similar situation occurs with a random function passed as actual argument. Call-by-name is known by many compiler designers for the interesting "
thunk In computer programming, a thunk is a subroutine used to inject a calculation into another subroutine. Thunks are primarily used to delay a calculation until its result is needed, or to insert operations at the beginning or end of the other sub ...
s" that are used to implement it. Donald Knuth devised the " man or boy test" to separate compilers that correctly implemented " recursion and non-local references." This test contains an example of call-by-name. ALGOL 68 was defined using a two-level grammar formalism invented by
Adriaan van Wijngaarden Adriaan "Aad" van Wijngaarden (2 November 1916 – 7 February 1987) was a Dutch mathematician and computer scientist. Trained as an engineer, Van Wijngaarden would emphasize and promote the mathematical aspects of computing, first in numerical an ...
and which bears his name.
Van Wijngaarden grammar In computer science, a Van Wijngaarden grammar (also vW-grammar or W-grammar) is a two-level grammar which provides a technique to define potentially infinite context-free grammars in a finite number of rules. The formalism was invented by Adria ...
s use a
context-free grammar In formal language theory, a context-free grammar (CFG) is a formal grammar whose production rules are of the form :A\ \to\ \alpha with A a ''single'' nonterminal symbol, and \alpha a string of terminals and/or nonterminals (\alpha can be emp ...
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.


Examples and portability issues


Code sample comparisons


ALGOL 60

(The way the bold text has to be written depends on the implementation, e.g. 'INTEGER'—quotation marks included—for integer. This is known as stropping.) procedure Absmax(a) Size:(n, m) Result:(y) Subscripts:(i, k); value n, m; array a; integer n, m, i, k; real y; comment The absolute greatest element of the matrix a, of size n by m is transferred to y, and the subscripts of this element to i and k; begin integer p, q; y := 0; i := k := 1; for p := 1 step 1 until n do for q := 1 step 1 until m do if abs(a , q > y then begin y := abs(a , q; i := p; k := q end end Absmax Here is an example of how to produce a table using Elliott 803 ALGOL. FLOATING POINT ALGOL TEST' BEGIN REAL A,B,C,D'   READ D'   FOR A:= 0.0 STEP D UNTIL 6.3 DO BEGIN PRINT PUNCH(3),££L??' B := SIN(A)' C := COS(A)' PRINT PUNCH(3),SAMELINE,ALIGNED(1,6),A,B,C' END' END' PUNCH(3) sends output to the teleprinter rather than the tape punch.
SAMELINE suppresses the carriage return + line feed normally printed between arguments.
ALIGNED(1,6) controls the format of the output with 1 digit before and 6 after the decimal point.


ALGOL 68

The following code samples are ALGOL 68 versions of the above ALGOL 60 code samples. ALGOL 68 implementations used ALGOL 60's approaches to stropping. In ALGOL 68's case tokens with the bold typeface are reserved words, types (modes) or operators. proc abs max = ( ''real a, ref real y, ref int i, k)real: comment The absolute greatest element of the matrix a, of size ⌈a by 2⌈a is transferred to y, and the subscripts of this element to i and k; comment begin real y := 0; i := ⌊a; k := 2⌊a; for p from ⌊a to ⌈a do for q from 2⌊a to 2⌈a do if abs a , q> y then y := abs a , q i := p; k := q fi od od; y end # abs max # Note: lower (⌊) and upper (⌈) bounds of an array, and array slicing, are directly available to the programmer. floating point algol68 test: ( real a,b,c,d;   # ''printf'' – sends output to the file ''stand out''. # # ''printf($p$);'' – selects a ''new page'' # printf(($pg$,"Enter d:")); read(d);   for step from 0 while a:=step*d; a <= 2*pi do printf($l$); # ''$l$'' - selects a ''new line''. # b := sin(a); c := cos(a); printf(($z-d.6d$,a,b,c)) # formats output with 1 digit before and 6 after the decimal point. # od )


Timeline: Hello world

The variations and lack of portability of the programs from one implementation to another is easily demonstrated by the classic
hello world program ''Hello'' is a salutation or greeting in the English language. It is first attested in writing from 1826. Early uses ''Hello'', with that spelling, was used in publications in the U.S. as early as the 18 October 1826 edition of the '' Norwich ...
.


ALGOL 58 (IAL)

ALGOL 58 had no I/O facilities.


ALGOL 60 family

Since ALGOL 60 had no I/O facilities, there is no portable
hello world program ''Hello'' is a salutation or greeting in the English language. It is first attested in writing from 1826. Early uses ''Hello'', with that spelling, was used in publications in the U.S. as early as the 18 October 1826 edition of the '' Norwich ...
in ALGOL. The next three examples are in Burroughs Extended Algol. The first two direct output at the interactive terminal they are run on. The first uses a character array, similar to C. The language allows the array identifier to be used as a pointer to the array, and hence in a REPLACE statement. A simpler program using an inline format: An even simpler program using the Display statement. Note that its output would end up at the system console ('SPO'): An alternative example, using Elliott Algol I/O is as follows. Elliott Algol used different characters for "open-string-quote" and "close-string-quote", represented here by and . Below is a version from Elliott 803 Algol (A104). The standard Elliott 803 used five-hole paper tape and thus only had upper case. The code lacked any quote characters so £ (UK Pound Sign) was used for open quote and ? (Question Mark) for close quote. Special sequences were placed in double quotes (e.g. ££L?? produced a new line on the teleprinter). HIFOLKS' BEGIN PRINT £HELLO WORLD£L??' END' The ICT 1900 series Algol I/O version allowed input from paper tape or punched card. Paper tape 'full' mode allowed lower case. Output was to a line printer. The open and close quote characters were represented using '(' and ')' and spaces by %. 'BEGIN' WRITE TEXT('('HELLO%WORLD')'); 'END'


ALGOL 68

ALGOL 68 code was published with reserved words typically in lowercase, but bolded or underlined. begin printf(($gl$,"Hello, world!")) end In the language of the "Algol 68 Report" the input/output facilities were collectively called the "Transput".


Timeline of ALGOL special characters

The ALGOLs were conceived at a time when character sets were diverse and evolving rapidly; also, the ALGOLs were defined so that only ''uppercase'' letters were required. 1960: IFIP – The Algol 60 language and report included several mathematical symbols which are available on modern computers and operating systems, but, unfortunately, were unsupported on most computing systems at the time. For instance: ×, ÷, ≤, ≥, ≠, ¬, ∨, ∧, ⊂, ≡, ␣ and ⏨. 1961 September: ASCII – The
ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
character set, then in an early stage of development, had the \ (Back slash) character added to it in order to support ALGOL's
boolean Any kind of logic, function, expression, or theory based on the work of George Boole is considered Boolean. Related to this, "Boolean" may refer to: * Boolean data type, a form of data with only two possible values (usually "true" and "false" ...
operators /\ and \/. 1962:
ALCOR ALCOR (ALGOL Converter, acronym) is an early computer language definition created by the ALCOR Group, a consortium of universities, research institutions and manufacturers in Europe and the United States which was founded in 1959 and which had 60 m ...
– This character set included the unusual "᛭" runic cross character for multiplication and the "⏨" Decimal Exponent Symbol for floating point notation. 1964:
GOST GOST (russian: ГОСТ) refers to a set of international technical standards maintained by the ''Euro-Asian Council for Standardization, Metrology and Certification (EASC)'', a regional standards organization operating under the auspices of ...
– The 1964 Soviet standard GOST 10859 allowed the encoding of 4-bit, 5-bit, 6-bit and 7-bit characters in ALGOL. 1968: The "Algol 68 Report" – used extant ALGOL characters, and further adopted →, ↓, ↑, □, ⌊, ⌈, ⎩, ⎧, ○, ⊥, and ¢ characters which can be found on the IBM 2741 keyboard with '' typeball'' (or ''golf ball'') print heads inserted (such as the APL golf ball). These became available in the mid-1960s while ALGOL 68 was being drafted. The report was translated into Russian, German, French, and Bulgarian, and allowed programming in languages with larger character sets, e.g.,
Cyrillic , bg, кирилица , mk, кирилица , russian: кириллица , sr, ћирилица, uk, кирилиця , fam1 = Egyptian hieroglyphs , fam2 = Proto-Sinaitic , fam3 = Phoenician , fam4 = Gr ...
alphabet of the Soviet
BESM BESM (БЭСМ) is the name of a series of Soviet mainframe computers built in 1950–60s. The name is an acronym for "Bolshaya Elektronno-Schetnaya Mashina" ("Большая Электронно-Счётная Машина"), literally "Large El ...
-4. All ALGOL's characters are also part of the Unicode standard and most of them are available in several popular
font In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a "sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design. In mod ...
s. 2009 October: Unicode – The (Decimal Exponent Symbol) for floating point notation was added to Unicode 5.2 for backward compatibility with historic
Buran programme The ''Buran'' program (russian: Буран, , "Snowstorm", "Blizzard"), also known as the "VKK Space Orbiter program" (russian: ВКК «Воздушно-Космический Корабль», lit=Air and Space Ship), was a Soviet Union, Sovi ...
ALGOL software.


See also


References


Further reading

* *
Brian Randell Brian Randell (born 1936) is a British computer scientist, and Emeritus Professor at the School of Computing, Newcastle University, United Kingdom. He specialises in research into software fault tolerance and dependability, and is a noted auth ...
and L. J. Russell
''ALGOL 60 Implementation: The Translation and Use of ALGOL 60 Programs on a Computer''. Academic Press, 1964. The design of the Whetstone Compiler
One of the early published descriptions of implementing a compiler. See the related papers
Whetstone Algol Revisited
an
The Whetstone KDF9 Algol Translator
by
Brian Randell Brian Randell (born 1936) is a British computer scientist, and Emeritus Professor at the School of Computing, Newcastle University, United Kingdom. He specialises in research into software fault tolerance and dependability, and is a noted auth ...
* *
Revised Report on the Algorithmic Language Algol 60
by Peter Naur, et al. ALGOL definition
"The European Side of the Last Phase of the Development of ALGOL 60" by Peter Naur


External links


History of ALGOL
at the Computer History Museum
Web enabled ALGOL-F compiler for small experiments

An online ALGOL compiler
{{DEFAULTSORT:Algol ALGOL 60 dialect Articles with example ALGOL 60 code Computer-related introductions in 1958 Procedural programming languages Programming languages created in 1958 Structured programming languages Systems programming languages