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{{short description|Family of programming languages}}{{about|the programming language family||Algol (disambiguation)}}{{Use dmy dates|date=July 2012}}

ALGOL ({{IPAc-en|ˈ|æ|l|g|ɒ|l|,_|-|g|ɔː|l}}; short for "Algorithmic Language")The name of this language family is sometimes given in mixed case (Algol 60 {{webarchive|url= |date=25 June 2007 }}), and sometimes in all uppercase (ALGOL68 {{webarchive|url= |date=13 September 2014 }}). For simplicity this article uses ALGOL. is a family of imperative computer programming languages, originally developed in the mid-1950s, which greatly influenced many other languages and was the standard method for algorithm description used by the ACM in textbooks and academic sources for more than thirty years.Collected Algorithms of the ACM {{webarchive|url= |date=17 October 2011 }} Compressed archives of the algorithms. ACM.In the sense that the syntax of most modern languages is "Algol-like",WEB,weblinkweblink" title="">weblink Algol-like languages, Introduction, P. W., O'Hearn, R. D., Tennent, September 1996, 14 November 2011, it was arguably the most influential of the four high-level programming languages among which it was roughly contemporary: FORTRAN, Lisp, and COBOL."The ALGOL Programming Language" {{webarchive|url= |date=6 October 2016 }}, University of Michigan-Dearborn It was designed to avoid some of the perceived problems with FORTRAN and eventually gave rise to many other programming languages, including PL/I, Simula, BCPL, B, Pascal, 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. 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, a principal formal grammar notation for language design.There were three major specifications, named after the year they were first published:
  • ALGOL 58 – originally proposed to be called IAL, for International Algebraic Language.
  • ALGOL 60 – first implemented as X1 ALGOL 60 in mid-1960. Revised 1963.BOOK, Report on the Algorithmic Language ALGOL 60, Copenhagen, May 1960, 10.1145/367236.367262, 0001-0782
editor1-last=Naurlast1=Backuslast2=Bauerlast3=Greenlast4=Katzlast5=McCarthylast6=Perlislast7=Rutishauserlast8=Samelsonlast9=Vauquoislast10=Wegsteinlast11=van Wijngaardenlast12=Woodger, WEB, Revised Report on the Algorithmic Language Algol 60, 1963,weblink 8 June 2007,weblink" title="">weblink 25 June 2007, live,
  • ALGOL 68 – introduced new elements including flexible arrays, slices, parallelism, operator identification. Revised 1973.WEB, Revised Report on the Algorithmic Language ALGOL 68, 1973,weblink 13 September 2014, live,weblink" title="">weblink 13 September 2014, dmy-all,
ALGOL 68 is substantially different from ALGOL 60 and was not well received, so that in general "Algol" means ALGOL 60 and dialects thereof.

Important implementations

The International Algebraic Language (IAL), or ALGOL 58, was extremely influential and generally considered the ancestor of most of the modern programming languages (the so-called Algol-like languages). Additionally, ALGOL object code was a simple, compact, and stack-based instruction set architecture commonly used in teaching compiler construction and other high order languages (of which Algol is generally considered the first).


ALGOL was developed jointly by a committee of European and American computer scientists in a meeting in 1958 at ETH Zurich (cf. ALGOL 58). 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. 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 for ALGOL 60, and at Donald Knuth's suggestion renamed Backus–Naur form.JOURNAL, Knuth, Donald E., 1964, Backus Normal Form vs Backus Naur Form, Communications of the ACM, 7, 12, 735–736, 10.1145/355588.365140, 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 {{webarchive|url= |date=2 April 2012 }}, 2005The following people attended the meeting in Paris (from 1 to 16 January): 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.""Hints on Programming Language Design" {{webarchive|url= |date=15 September 2009 }}, C.A.R. Hoare, December 1973. Page 27. (This statement is sometimes erroneously attributed to Edsger W. Dijkstra, also involved in implementing the first ALGOL 60 compiler.) The Scheme 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.WEB, Jonathan Rees, William Clinger Hal Abelson, R. K. Dybvig, Revised(3) Report on the Algorithmic Language Scheme, (Dedicated to the Memory of ALGOL 60),weblink 20 October 2009, etal, live,weblink" title="">weblink 14 January 2010, dmy-all,

Algol and programming language research

As Peter Landin noted, the language Algol was the first language to combine seamlessly imperative effects with the (call-by-name) lambda calculus. Perhaps the most elegant formulation of the language is due to John C. Reynolds, and it best exhibits its syntactic and semantic purity. Reynolds's idealized Algol also made a convincing methodological argument regarding the suitability of local effects in the context of call-by-name languages, to be contrasted with the global effects used by call-by-value languages such as ML. The conceptual integrity of the language made it one of the main objects of semantic research, along with PCF and ML.Peter O'Hearn and Robert D. Tennent. 1996. Algol-Like Languages. Birkhauser Boston Inc., Cambridge, MA, USA.

IAL implementations timeline

To date there have been at least 70 augmentations, extensions, derivations and sublanguages of Algol 60.WEB,weblink The Encyclopedia of Computer Languages, 20 January 2012, dead,weblink" title="">weblink 27 September 2011, dmy, {| class="wikitable sortable"!|Name!|Year!|Author!|Country!|Description!|Target CPUFriedrich L. Bauer, Heinz Rutishauser, Klaus Samelson, Hermann Bottenbruch >ALGOL 58 >Z22 (computer)>Z22 (later Konrad Zuse's Z23 (computer)>Z23 was delivered with an Algol 60 compiler)Computer Museum History {{webarchiveweblink >date=20 August 2010 }}, Historical Zuse-Computer Z23, restored by the Konrad Zuse Schule in Hünfeld, for the Computer Museum History Center in Mountain View (California) USALAST=DAYLIGHT JOURNAL=THE COMPUTER JOURNAL DOI=10.1093/COMJNL/BXR002 PAGES=1756–1772 URL-STATUS=LIVE ARCHIVEDATE=12 MARCH 2013 Edsger W. Dijkstra and (:nl:Jaap Zonneveld>Jaap A. Zonneveld) Netherlands First implementation of ALGOL 60KRUSEMAN ARETZ > FIRST1 = F.E.J. TITLE = SOFTWARE ENGINEERING PUBLISHER = CENTRUM WISKUNDE & INFORMATICA DATE = 30 JUNE 2003 URL-STATUS = LIVE ARCHIVEDATE = 4 MARCH 2016 | Electrologica X1Elliott ALGOL>C. A. R. Hoare >Turing Award>Turing lectureANTONY>LAST=HOAREJOURNAL=COMMUNICATIONS OF THE ACMNUMBER=2URL=HTTP://AMTURING.ACM.ORG/AWARD_WINNERS/HOARE_4622167.CFMURL-STATUS=LIVEARCHIVEDATE=13 SEPTEMBER 2017| Elliott 803, Elliott 503, Elliott 4100 seriesJOVIAL>Jules Schwartz >United States Department of Defense>DOD High level language prior to Ada (programming language)>Ada Various (see article)Burroughs large systems#ALGOL>Burroughs Algol (Several variants) 1961 Burroughs Corporation (with participation by Hoare, Edsger W. Dijkstra, and others) >Burroughs Corporation>Burroughs (and now Unisys Burroughs MCP based) computers >| Burroughs large systems and their midrange as well.Case ALGOL>Case Western Reserve University>Case Institute of TechnologyKOFFMAN>FIRST=ELIOTURL=HTTP://WWW.TEMPLE.EDU/CIS/DIRECTORY/TENURE/DOCUMENTS/KOFFMANSIGCSESLIDES.PDFURL-STATUS=DEADARCHIVEDATE=12 OCTOBER 2012Simula was originally contracted as a simulation extension of the Case ALGOL >| UNIVAC 1107GOGOL>William M. McKeeman >ACCESSDATE=1 FEB 2018URL-STATUS=LIVEARCHIVEDATE=2 FEBRUARY 2018| PDP-1RegneCentralen ALGOL>Peter Naur, Jørn Jensen >| DASK at RegnecentralenDartmouth ALGOL 30>Thomas Eugene Kurtz et al. >| LGP-30USS 90 Algol>L. Petrone >|Willem van der Poel>W.L. van der Poel Netherlands Staatsbedrijf der Posterijen, Telegrafie en Telefonie ZEBRAKidsgrove Algol>F. G. Duncan >English Electric>English Electric Company KDF9VALGOL>Val Schorre >| A test of the META II compiler compilerWhetstone (benchmark)>Whetstone 1964 Brian Randell and L. J. Russell UK Atomic Power Division of English Electric Company. Precursor to Ferranti Pegasus, National Physical Laboratories Automatic Computing Engine and English Electric DEUCE implementations. >English Electric KDF9>KDF9NU ALGOL>| UNIVACSoviet Union>USSR АЛГЭК, based on ALGOL-60 and COBOL support, for economical tasks Minsk-22ALGOL W>Niklaus Wirth >| IBM System/360MALGOL>Estonian Soviet Socialist Republic>Estonian SSR Minsk-22ALGAMS>Comecon >Minsk family of computers>Minsk-22, later ES EVM, BESMALGOL/ZAM>ZAM (computer)>ZAM computerSimula>Simula 67 1967 Ole-Johan Dahl and Kristen Nygaard Norway Algol 60 with classes UNIVAC 1107weblink" title="">Chinese Algol>| Chinese characters, expressed via the Symbol systemDG/L>Data General Eclipse>Eclipse family of ComputersS-algol>Ron Morrison >| PDP-11 with a subsequent implementation on the Java VMThe Burroughs dialects included special Bootstrapping dialects such as ESPOL and NEWP. The latter is still used for Unisys MCP system software.


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, and call-by-name. Call-by-name has certain effects in contrast to call-by-reference. 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.BOOK, Aho, Alfred V., Alfred V. Aho, Ravi Sethi, Ravi Sethi, Jeffrey D. Ullman, Jeffrey Ullman, (Dragon Book (computer science), Compilers: Principles, Techniques, and Tools), 1986, 1st, Addison-Wesley, 0-201-10194-7, , Section 7.5, and references therein Think of passing a pointer to swap(i, A[i]) in to a function. Now that every time swap is referenced, it is reevaluated. Say i := 1 and A[i] := 2, so every time swap is referenced it'll return the other combination of the values ([1,2], [2,1], [1,2] and 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 "thunks" 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 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.

Examples and portability issues

Code sample comparisons


(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;
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[p, q]) > y then
begin y := abs(a[p, q]);
i := p; k := q
end Absmax
Here is an example of how to produce a table using Elliott 803 ALGOL."803 ALGOL" {{webarchive|url= |date=29 May 2010 }}, the manual for Elliott 803 ALGOL
B := SIN(A)'
C := COS(A)'
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.


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
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[p, q] > y then
y := abs a[p, q];
i := p; k := q
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:"));
for step from 0 while a:=step*d; a

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