View source for ALGOL 60

{{Short description|Member of the ALGOL family of computer programming languages}}
{{About|the programming language||Algol (disambiguation)}}
{{Infobox programming language
| name = ALGOL 60
| paradigms = [[Procedural programming|procedural]], [[Imperative programming|imperative]], [[Structured programming|structured]]
| family = [[ALGOL]]
| designers = [[John Warner Backus|Backus]], [[Friedrich Ludwig Bauer|Bauer]], [[Julien Green (computer scientist)|Green]], [[Charles Katz|Katz]], [[John McCarthy (computer scientist)|McCarthy]], [[Peter Naur|Naur]], [[Alan Jay Perlis|Perlis]], [[Heinz Rutishauser|Rutishauser]], [[Klaus Samelson|Samelson]], [[Adriaan van Wijngaarden|van Wijngaarden]], [[Bernard Vauquois|Vauquois]], [[Joseph Henry Wegstein|Wegstein]], [[Michael Woodger|Woodger]]
| released = {{Start date and age|1960}}
| typing = [[Static type|Static]], [[Strong and weak typing|strong]]
| scope = [[Scope (computer science)|Lexical]]
| influenced by = [[ALGOL 58]]
| influenced = Most subsequent imperative languages (so-called ''ALGOL-like'' languages), e.g., [[PL/I]],  [[Simula]], [[Combined Programming Language|CPL]], [[Pascal (programming language)|Pascal]], [[Ada (programming language)|Ada]], [[C (programming language)|C]]
}}
'''ALGOL 60''' (short for ''Algorithmic Language 1960'') is a member of the [[ALGOL]] family of computer [[programming language]]s. It followed on from [[ALGOL 58]] which had introduced [[Block (programming)|code blocks]] and the <code>begin</code> and <code>end</code> pairs for delimiting them, representing a key advance in the rise of [[structured programming]]. ALGOL 60 was one of the first languages implementing function definitions (that could be invoked recursively). ALGOL 60 function definitions could be [[nested function|nested]] within one another (which was first introduced by any programming language{{Clarify|date=December 2024}}), with [[lexical scope]]. It gave rise to many other languages, including [[CPL (programming language)|CPL]], [[PL/I]], [[Simula]], [[BCPL]], [[B (programming language)|B]], [[Pascal (programming language)|Pascal]], and [[C (programming language)|C]]. Practically every computer of the era had a [[systems programming language]] based on ALGOL 60 concepts.

[[Niklaus Wirth]] based his own [[ALGOL W]] on ALGOL 60 before moving to develop [[Pascal (programming language)|Pascal]]. Algol-W was intended to be the next generation ALGOL but the [[ALGOL 68]] committee decided on a design that was more complex and advanced rather than a cleaned simplified ALGOL 60. The official ALGOL versions are named after the year they were first published. ALGOL 68 is substantially different from ALGOL 60 and was criticised partially for being so, so that in general "ALGOL" refers to dialects of ALGOL 60.

==Standardization==
ALGOL 60 – with [[COBOL]] – were the first languages to seek standardization.
* [http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=6126 ISO 1538:1984] Programming languages – ALGOL 60 (stabilized)
* [http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=6286 ISO/TR 1672:1977] Hardware representation of ALGOL basic symbols ... (now withdrawn)

==History==
ALGOL 60 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. 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–Naur form|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]].<ref>{{cite journal |last=Knuth |first=Donald E. |author-link=Donald Knuth |title=Backus normal Form vs Backus Naur Form |journal=Communications of the ACM |volume=7 |issue=12 |pages=735–6 |date=December 1964 |doi=10.1145/355588.365140 |s2cid=47537431|doi-access=free }}</ref>

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."<ref name="naur_acm">[http://awards.acm.org/citation.cfm?id=1024454&srt=all&aw=140&ao=AMTURING&yr=2005 ACM Award Citation / Peter Naur], 2005</ref>

The following people attended the meeting in Paris (from January 11 to 16):
* [[Friedrich Ludwig Bauer]], [[Peter Naur]], [[Heinz Rutishauser]], [[Klaus Samelson]], [[Bernard Vauquois]], [[Adriaan van Wijngaarden]], and [[Michael Woodger]] (from Europe)
* [[John Warner Backus]], [[Julien Green (computer scientist)|Julien Green]], [[Charles Katz]], [[John McCarthy (computer scientist)|John McCarthy]], [[Alan Jay Perlis]], and [[Joseph Henry Wegstein]] (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."

The language originally did not include [[recursion]]. It was inserted into the specification at the last minute, against the wishes of some of the committee.<ref>{{cite web|url=https://vanemden.wordpress.com/2014/06/18/how-recursion-got-into-programming-a-comedy-of-errors-3/|title=How recursion got into programming: a tale of intrigue, betrayal, and advanced programming-language semantics|first=Maarten|last=van Emden|date=2014|series=''A Programmer's Place''}}</ref>

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."<ref>{{cite web |last=Hoare |first=C.A.R. |author-link=Tony Hoare |title=Hints on Programming Language Design |date=December 1973 |url=http://www.eecs.umich.edu/~bchandra/courses/papers/Hoare_Hints.pdf |page=27}} (This statement is sometimes erroneously attributed to [[Edsger W. Dijkstra]], also involved in implementing the first ALGOL 60 [[compiler]].)</ref><ref name="r3rs">{{cite web |last1=Abelson |first1=Hal |author1-link=Hal Abelson |last2=Dybvig |first2=R. K. |author2-link=R. Kent Dybvig |editor1-last=Rees |editor1-first=Jonathan |editor2-last=Clinger |editor2-first=William |title=Revised(3) Report on the Algorithmic Language Scheme (Dedicated to the Memory of ALGOL 60)
|url=http://groups.csail.mit.edu/mac/ftpdir/scheme-reports/r3rs-html/r3rs_toc.html
|access-date=2009-10-20
|display-authors=etal}}</ref>

===ALGOL 60 implementations timeline===
To date there have been at least 70 augmentations, extensions, derivations and sublanguages of ALGOL 60.<ref>[http://hopl.murdoch.edu.au/showlanguage.prx?exp=1807 The Encyclopedia of Computer Languages<!-- Bot generated title -->] {{webarchive |url=https://web.archive.org/web/20110927014141/http://hopl.murdoch.edu.au/showlanguage.prx?exp=1807 |date=September 27, 2011}}</ref>

{|class="wikitable" style="border-collapse: collapse;"
|-
!|Name
!|Year
!|Author
!|State
!|Description
!|Target CPU
|-
| X1 ALGOL 60 || August 1960<ref>{{cite journal|url=http://www.dijkstrascry.com/node/4
|title=Dijkstra's Rallying Cry for Generalization: the Advent of the Recursive Procedure, late 1950s – early 1960s
|last=Daylight |first=E. G.
|journal=[[The Computer Journal]]
|volume=54
|issue=11
|year=2011
|pages=1756–1772
|doi=10.1093/comjnl/bxr002
|url-access=subscription
}}</ref> || [[Edsger W. Dijkstra]] and [[:nl:Jaap Zonneveld|Jaap A. Zonneveld]] || {{flag|Netherlands}} || First implementation of ALGOL 60<ref>{{Cite book |last1=Kruseman Aretz |first1=F.E.J. |chapter=The Dijkstra-Zonneveld ALGOL 60 compiler for the Electrologica X1 |title=Software Engineering |series=History of Computer Science |publisher=Centrum Wiskunde & Informatica |location=Amsterdam |date=30 June 2003 |issn=1386-3711 |chapter-url=http://www.cwi.nl/ftp/CWIreports/SEN/SEN-N0301.pdf |archive-url=https://web.archive.org/web/20040117172550/http://ftp.cwi.nl/CWIreports/SEN/SEN-N0301.pdf |archive-date=2004-01-17 |url-status=dead}}</ref> || [[Electrologica X1]]
|-
| Algol || 1960<ref>[[Edgar T. Irons|Irons, Edgar T.]], A syntax directed compiler for ALGOL 60, Communications of the ACM, Vol. 4, p. 51. (Jan. 1961)</ref>|| Edgar T. Irons || {{flag|USA}} || ALGOL 60 || [[CDC 1604]] 
|-
| [[Burroughs Large Systems#ALGOL|Burroughs Algol]]<br/>(Several variants) || 1961 || [[Burroughs Corporation]] (with participation by [[Tony Hoare|Hoare]], [[Edsger W. Dijkstra|Dijkstra]], and others) || {{flag|USA}} || Basis of the [[Burroughs Corporation|Burroughs]] (and now [[Unisys]] [[Burroughs MCP|MCP]] based) computers || [[Burroughs Large Systems]]<br/>and midrange systems
|-
| [[Case ALGOL]] || 1961 || || {{flag|USA}} || [[Simula]] was originally contracted as a simulation extension of the Case ALGOL || [[UNIVAC 1107]]
|-
| [[GOGOL]] || 1961 || [[William M. McKeeman]] || {{flag|USA}} || For ODIN time-sharing system || [[PDP-1]]
|-
| [[DASK ALGOL]] || 1961 || [[Peter Naur]], [[Jørn Jensen]] || {{flag|Denmark}} || ALGOL 60 || DASK at Regnecentralen
|-
| [[SMIL ALGOL]] || 1962 || [[Torgil Ekman]], [[Carl-Erik Fröberg]] || {{flag|Sweden}} || ALGOL 60 || [[SMIL (computer)|SMIL]] at [[Lund University]]
|-
| [[GIER ALGOL]] || 1962 || [[Peter Naur]], [[Jørn Jensen]] || {{flag|Denmark}} || ALGOL 60 || GIER at Regnecentralen
|-
| [[Dartmouth ALGOL 30]]{{sfn|Kurtz|1978}} || 1962 || [[Thomas Eugene Kurtz]], [[Stephen J. Garland]], Robert F. Hargraves, [[Anthony W. Knapp]], [[Jorge LLacer]] || {{flag|USA}} || ALGOL 60 || [[LGP-30]]
|-
| Alcor Mainz 2002 || 1962 || Ursula Hill-Samelson, Hans Langmaack || {{flag|Germany}} || || Siemens 2002
|-
| ALCOR-Illinois 7090
|| 1962<br/><ref>{{Cite journal |last1=Gries |first1=D. |last2=Paul |first2=M. |last3=Wiehle |first3=H. R |year=1965 |doi=10.1145/365474.365511 |title=Some techniques used in the ALCOR Illinois 7090 |journal=Communications of the ACM |volume=8 |issue=8 |pages=496–500 |s2cid=18365024|doi-access=free }}</ref><ref>{{Cite journal |last1=Bayer |first1=R. |last2=Gries |first2=D. |last3=Paul |first3=M. |last4=Wiehle |first4=H. R. |year=1967 |title=The ALCOR Illinois 7090/7094 post mortem dump |journal=Communications of the ACM |volume=10 |issue=12 |pages=804–808 |doi=10.1145/363848.363866 |s2cid=3783605 |doi-access=free}}</ref>
|| [[:de:Manfred Paul (Informatiker)|Manfred Paul]], Hans Rüdiger Wiehle, [[David Gries]], and [[Rudolf Bayer]]
|| {{flag|USA}}, {{flag|West Germany}}
|| ALGOL 60<br/>Implemented at [[University of Illinois Urbana-Champaign|Illinois]] and the [[Technical University of Munich|TH München]], 1962-1964
|| [[IBM 7090]]
|-
| [[USS 90 Algol]] || 1962 || [[L. Petrone]]<!-- ? --> || {{flag|Italy}} ||
|-
| [[Elliott ALGOL]] || 1962 || [[C. A. R. Hoare]] || {{flag|UK}} || Discussed in his 1980 [[Turing Award]] lecture|| [[Elliott 803]] & the Elliott 503
|-
| ALGOL 60 || 1962 || Roland Strobel<ref>[http://www.fv-tsd.de/index.php?id=42 Rechenautomaten mit Trommelspeicher], Förderverein der Technischen Sammlung Dresden</ref> || {{flag|East Germany}} || Implemented by the Institute for Applied Mathematics, [[German Academy of Sciences at Berlin]] || Zeiss-Rechenautomat ZRA 1
|-
|ALGOL 60
|1962
|[[Bernard Vauquois]], Louis Bolliet<ref>{{Cite journal |last=Mounier-Kuhn |first=Pierre |date=2014 |title=Algol in France: From Universal Project to Embedded Culture |url=https://www.academia.edu/79159820 |journal=IEEE Annals of the History of Computing |volume=36 |issue=4 |pages=6–25 |doi=10.1109/MAHC.2014.50 |issn=1058-6180}}</ref>
| {{flag|France}}
|Institut d'Informatique et Mathématiques Appliquées de Grenoble (IMAG) and Compagnie des Machines Bull
|[[Bull Gamma 60]]
|-
| Algol Translator || 1962 || G. van der Mey and [[Willem van der Poel|W.L. van der Poel]] || {{flag|Netherlands}} || Staatsbedrijf der Posterijen, Telegrafie en Telefonie || [[ZEBRA (computer)|ZEBRA]]
|-
| [[Kidsgrove Algol]] || 1963 || [[F. G. Duncan]]<!-- ? --> || {{flag|UK}} || || [[English Electric|English Electric Company]] [[English Electric KDF9|KDF9]]
|-
| SCALP{{sfn|Kurtz|1978|p=517}} || 1963 || [[Stephen J. Garland]], [[Anthony W. Knapp]], [[Thomas Eugene Kurtz]] || {{flag|USA}} || ''Self-Contained ALgol Processor'' for a subset of ALGOL 60 || [[LGP-30]]
|-
| [[VALGOL]] || 1963 || [[Val Schorre]] || {{flag|USA}} || A test of the [[META II]] compiler compiler
|-
| FP6000 Algol || 1963 || [[Roger Moore (computer scientist)|Roger Moore]] || {{flag|Canada}} || written for [[SaskPower|Saskatchewan Power Corp]] || [[Ferranti-Packard 6000|FP6000]] 
|-
| [[Whetstone (benchmark)|Whetstone]] || 1964 || [[Brian Randell]] and Lawford John Russell || {{flag|UK}} || Atomic Power Division of English Electric Company. Precursor to [[Ferranti Pegasus]], National Physical Laboratories [[Automatic Computing Engine|ACE]] and [[English Electric DEUCE]] implementations || English Electric Company [[English Electric KDF9|KDF9]]
|- 
| ALGOL 60 || 1964 || Jean-Claude Boussard<ref>{{cite thesis |title=Etude et réalisation d'un compilateur Algol60 sur calculateur éléctronique du type IBM 7090/94 et 7040/44 |trans-title=Design and implementation of a compiler Algol60 on electronic calculator IBM 7090/94 and 7040/44 |last=Boussard |first=Jean-Claude |date=June 1964 |publisher=Université Joseph-Fourier - Grenoble I |url=https://tel.archives-ouvertes.fr/tel-00009449| type=PhD |language=fr}}</ref> || {{flag|France}} || {{ill|Institut d'informatique et mathématiques appliquées de Grenoble|fr}} || [[IBM 7090]]
|-
| ALGOL-GENIUS || 1964 || Börje Langefors || {{flag|Sweden}} || Added [[COBOL]]-inspired data records and I/O || [[Datasaab]] D-21
|-
| ALGOL 60 || 1965 || {{ill|Claude Pair|fr}}<ref>{{cite conference| title=Description d'un compilateur ALGOL| author=Claude Pair| date=27 April 1965 |journal=European Région 1620 Users Group |publisher=IBM}}</ref> || {{flag|France}} || Centre de calcul de la Faculté des Sciences de Nancy || [[IBM 1620]]
|-
| Dartmouth ALGOL || 1965 || [[Stephen J. Garland]], Sarr Blumson, Ron Martin || {{flag|USA}} || ALGOL 60 || [[Dartmouth Time-Sharing System]] for the [[GE-200 series|GE 235]]
|-
| [[NU ALGOL]] || 1965 || || {{flag|Norway}} || || [[UNIVAC]]
|-
| ALGOL 60 || 1965<ref>{{Cite book |last1=Kruseman Aretz |first1=F.E.J. |title=An Algol 60 compiler in Algol 60 |series=Mathematical Centre Tracts |publisher=Mathematisch Centrum |place=Amsterdam |date=1973}}</ref> || F.E.J. Kruseman Aretz || {{flag|Netherlands}} || MC compiler for the EL-X8 || [[Electrologica X8]]
|-
|ALGEK|| 1965 || || {{flag|USSR}} || [[Minsk family of computers|Minsk-22]] || АЛГЭК, based on ALGOL 60 and [[COBOL]] support, for economical tasks

|-
| [[MALGOL]] || 1966 || publ. A. Viil, M Kotli & M. Rakhendi, || {{flag|Estonian SSR}} || [[Minsk family of computers|Minsk-22]]
|-
| [[ALGAMS]] || 1967 || GAMS group (ГАМС, группа автоматизации программирования для машин среднего класса), cooperation of Comecon Academies of Science || [[Comecon]] || [[Minsk family of computers|Minsk-22]], later [[ES EVM]], [[BESM]]
|-
| [[ALGOL/ZAM]] || 1967 || || {{flag|Poland}} || || Polish [[ZAM (computer)|ZAM]] computer
|-
|[https://web.archive.org/web/20080722231533/http://hopl.murdoch.edu.au/showlanguage.prx?exp=7288&language=Chinese%20Algol Chinese Algol]|| 1972 || 
| {{flag|China}} || Chinese characters, expressed via the Symbol system
|-
| [[DG/L]] || 1972 || || {{flag|USA}} || || DG [[Data General Eclipse|Eclipse]] family of Computers
|-
|[http://www.bertnase.de/a60/ NASE]||1990||Erik Schoenfelder ||{{flag|Germany}}||Interpreter ||Linux and MS Windows
|- 
|[https://www.gnu.org/software/marst/ MARST] ||2000||Andrew Makhorin||{{flag|Russia}}||ALGOL 60 to C translator||All CPUs supported by the GNU Compiler Collection; MARST is part of the GNU project
|}

The Burroughs dialects included special system programming dialects such as [[Executive Systems Problem Oriented Language|ESPOL]] and [[NEWP]].

==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'' (ALGOL 68 parlance for input/output) facilities.

ALGOL 60 provided two [[evaluation strategy|evaluation strategies]] for [[Parameter (computer science)|parameter]] passing: the common [[call-by-value]], and [[call-by-name]]. The procedure declaration specified, for each formal parameter, which was to be used: ''value'' specified for call-by-value, and omitted for 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.<ref>{{cite book |last1=Aho |first1=Alfred V. |author1-link=Alfred V. Aho |last2=Sethi |first2=Ravi |author2-link=Ravi Sethi |last3=Ullman |first3=Jeffrey D. |author3-link=Jeffrey Ullman |year=1986 |title=Compilers: Principles, Techniques, and Tools |edition=1st |publisher=Addison-Wesley |isbn=978-0-201-10194-2 |title-link=Dragon Book (computer science)}}, Section 7.5, and references therein</ref> Think of passing a pointer to swap(i, A[i]) in to a function. Now that every time swap is referenced, it's 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 "[[Thunk (delayed computation)|thunk]]s" that are used to implement it. [[Donald Knuth]] devised the "[[man or boy test]]" to separate compilers that correctly implemented "[[recursion (computer science)|recursion]] and non-local references." This test contains an example of call-by-name.

=== Language levels ===
The ALGOL 60 reports recognize three different levels of language, i.e., a Reference Language, a Publication Language, and several Hardware Representations. The Reference and Publication languages have no reserved words, however the reports do recommend<ref>{{Harvnb|Naur et al.|1963|loc=3.2.4. Standard functions}}
</ref> reserving some identifiers for standard functions.

The reports briefly describe hardware representations. Implementations differ in their hardware representations of underlined independent basic symbols<ref>{{Harvnb |Naur et al. |1963 |loc=2.1. Letters}}: (1) It should be particularly noted that throughout the reference language underlining [here this looks like underlined; N.L.] is used for defining independent basic symbols (see sections 2.2.2 and 2.3). These are understood to have no relation to the individual letters of which they are composed. Within the present report underlining will be used for no other purposes.
</ref>
# Reserved words
# [[Stropping (syntax)|Stropping]]

===ALGOL 60 Reserved words and restricted identifiers===
There are 24 reserved words in the Modified Report:

{{div col|colwidth=7em}}
*<code>ARRAY</code>
*<code>BEGIN</code>
*<code>BOOLEAN</code>
*<code>COMMENT</code>
*<code>DO</code>
*<code>ELSE</code>
*<code>END</code>
*<code>FALSE</code>
*<code>FOR</code>
*<code>GOTO</code>
*<code>IF</code>
*<code>INTEGER</code>
*<code>LABEL</code>
*<code>OWN</code>
*<code>PROCEDURE</code>
*<code>REAL</code>
*<code>STEP</code>
*<code>STRING</code>
*<code>SWITCH</code>
*<code>THEN</code>
*<code>TRUE</code>
*<code>UNTIL</code>
*<code>VALUE</code>
*<code>WHILE</code>
{{div col end}}There are 35 such reserved words in the standard [[Burroughs Large Systems]] sub-language:

{{div col|colwidth=7em}}
*<code>ALPHA</code>
*<code>ARRAY</code>
*<code>BEGIN</code>
*<code>BOOLEAN</code>
*<code>COMMENT</code>
*<code>CONTINUE</code>
*<code>DIRECT</code>
*<code>DO</code>
*<code>DOUBLE</code>
*<code>ELSE</code>
*<code>END</code>
*<code>EVENT</code>
*<code>FALSE</code>
*<code>FILE</code>
*<code>FOR</code>
*<code>FORMAT</code>
*<code>GO</code>
*<code>IF</code>
*<code>INTEGER</code>
*<code>LABEL</code>
*<code>LIST</code>
*<code>LONG</code>
*<code>OWN</code>
*<code>POINTER</code>
*<code>PROCEDURE</code>
*<code>REAL</code>
*<code>STEP</code>
*<code>SWITCH</code>
*<code>TASK</code>
*<code>THEN</code>
*<code>TRUE</code>
*<code>UNTIL</code>
*<code>VALUE</code>
*<code>WHILE</code>
*<code>ZIP</code>
{{div col end}}

There are 71 such restricted identifiers in the standard Burroughs Large Systems sub-language: 
{{div col|colwidth=7em}}
*<code>ACCEPT</code>
*<code>AND</code>
*<code>ATTACH</code>
*<code>BY</code>
*<code>CALL</code>
*<code>CASE</code>
*<code>CAUSE</code>
*<code>CLOSE</code>
*<code>DEALLOCATE</code>
*<code>DEFINE</code>
*<code>DETACH</code>
*<code>DISABLE</code>
*<code>DISPLAY</code>
*<code>DIV</code>
*<code>DUMP</code>
*<code>ENABLE</code>
*<code>EQL</code>
*<code>EQV</code>
*<code>EXCHANGE</code>
*<code>EXTERNAL</code>
*<code>FILL</code>
*<code>FORWARD</code>
*<code>GEQ</code>
*<code>GTR</code>
*<code>IMP</code>
*<code>IN</code>
*<code>INTERRUPT</code>
*<code>IS</code>
*<code>LB</code>
*<code>LEQ</code>
*<code>LIBERATE</code>
*<code>LINE</code>
*<code>LOCK</code>
*<code>LSS</code>
*<code>MERGE</code>
*<code>MOD</code>
*<code>MONITOR</code>
*<code>MUX</code>
*<code>NEQ</code>
*<code>NO</code>
*<code>NOT</code>
*<code>ON</code>
*<code>OPEN</code>
*<code>OR</code>
*<code>OUT</code>
*<code>PICTURE</code>
*<code>PROCESS</code>
*<code>PROCURE</code>
*<code>PROGRAMDUMP</code>
*<code>RB</code>
*<code>READ</code>
*<code>RELEASE</code>
*<code>REPLACE</code>
*<code>RESET</code>
*<code>RESIZE</code>
*<code>REWIND</code>
*<code>RUN</code>
*<code>SCAN</code>
*<code>SEEK</code>
*<code>SET</code>
*<code>SKIP</code>
*<code>SORT</code>
*<code>SPACE</code>
*<code>SWAP</code>
*<code>THRU</code>
*<code>TIMES</code>
*<code>TO</code>
*<code>WAIT</code>
*<code>WHEN</code>
*<code>WITH</code>
*<code>WRITE</code> 
{{div col end}}

and also the names of all the intrinsic functions.

====Standard operators====
{| class="wikitable"
! colspan="2" |Priority
! Operator
|-
| rowspan="3" | first arithmetic || first || ↑ (power)
|-
| second || ×, / (real), ÷ (integer)
|-
| third || +, -
|-
| colspan="2"| second || <, ≤, =, ≥, >, ≠
|-
| colspan="2"| third || ¬ (not)
|-
| colspan="2" | fourth || ∧ (and)
|-
| colspan="2" | fifth || ∨ (or)
|-
| colspan="2" | sixth || ⊃ (implication)
|-
| colspan="2" | seventh || ≡ (equivalence)
|}

==Examples and portability issues==

===Code sample comparisons===

====ALGOL 60====

 '''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 copied 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[p, q]) > y '''then'''
                 '''begin''' y := abs(a[p, q]);
                     i := p; k := q
                 '''end'''
 '''end''' Absmax;

Implementations differ in how the text in bold must be written. The word 'INTEGER', including the quotation marks, must be used in some implementations in place of '''integer''', above, thereby [[stropping (syntax)|designating]] it as a special keyword.

Following is an example of how to produce a table using [[Elliott 803]] ALGOL:<ref>[http://www.billp.org/ccs/A104/ "803 ALGOL"], the manual for [[Elliott 803]] ALGOL</ref>

  FLOATING POINT ALGOL TEST'
  BEGIN REAL A,B,C,D'
 
  READ D'
 
  FOR A:= 0.0 STEP D UNTIL 6.3 DO
  BEGIN
    PRINT {{abbr|PUNCH(3)|sends output to the teleprinter rather than the tape punch.}},££L??'
    B := SIN(A)'
    C := COS(A)'
    PRINT {{abbr|PUNCH(3)|sends output to the teleprinter rather than the tape punch.}},{{abbr|SAMELINE|suppresses the carriage return + line feed normally printed between arguments.}},{{abbr|ALIGNED(1,6)|controls the format of the output with 1 digit before and 6 after the decimal point.}},A,B,C'
  END'
  END'

====ALGOL 60 family====
Since ALGOL 60 had no I/O facilities, there is no portable [[hello world program]] in ALGOL. The following program could (and still will) compile and run on an ALGOL implementation for a Unisys A-Series mainframe, and is a straightforward simplification of code taken from The Language Guide<ref>{{cite web |url=http://www.engin.umd.umich.edu/CIS/course.des/cis400/ |title=The ALGOL Programming Language |website=www.engin.umd.umich.edu |access-date=11 January 2022 |archive-url=https://web.archive.org/web/20100210185248/http://www.engin.umd.umich.edu/CIS/course.des/cis400/algol/algol.html |archive-date=10 February 2010 |url-status=dead}}</ref> at the [[University of Michigan]]-Dearborn Computer and Information
Science Department Hello world! ALGOL Example Program page.<ref>{{cite web |url=http://www.engin.umd.umich.edu/CIS/course.des/cis400/algol/hworld.html |title=Hello world! Example Program |website=www.engin.umd.umich.edu |access-date=11 January 2022 |archive-url=https://web.archive.org/web/20100204112923/http://www.engin.umd.umich.edu/CIS/course.des/cis400/algol/hworld.html |archive-date=4 February 2010 |url-status=dead}}</ref>

 BEGIN
   FILE F(KIND=REMOTE);
   [[EBCDIC]] ARRAY E[0:11];
   REPLACE E BY "HELLO WORLD!";
   WRITE(F, *, E);
 END.

Where * etc. represented a format specification as used in FORTRAN, e.g.<ref>[[Fortran#"Hello, World!" example]]</ref>

A simpler program using an inline format:
{{sxhl|2=m2|1=<nowiki/>
 BEGIN
   FILE F(KIND=REMOTE);
   WRITE(F, <"HELLO WORLD!">);
 END.
}}
An even simpler program using the Display statement:

{{sxhl|2=m2|1= BEGIN DISPLAY("HELLO WORLD!") END.}}

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 {{color box|rgba(255,255,255,0)|border=silver| [[‘]]}} and {{color box|rgba(255,255,255,0)|border=silver| [[Single quotation mark|’]]}}.
{{sxhl|2=pascal|1=<nowiki/>
 program HiFolks;
 begin
    print ‘Hello world’
 end;
}}
Here's a version for the Elliott 803 Algol (A104) The standard Elliott 803 used 5-hole paper tape and thus only had upper case. The code lacked any quote characters so [[£]] (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. Note use of '(', ')', and %.<ref>{{cite web|url=http://www.icl1900.co.uk/techpub/tp3340.djvu|title=ICL 1900 series: Algol Language|publisher=ICL Technical Publication 3340|year=1965}}</ref>
   'PROGRAM' (HELLO)
   'BEGIN'
      'COMMENT' OPEN QUOTE IS '(', CLOSE IS ')', PRINTABLE SPACE HAS TO
                BE WRITTEN AS % BECAUSE SPACES ARE IGNORED;
      WRITE TEXT('('HELLO%WORLD')');
   'END'
   'FINISH'

==LEAP==

LEAP is an extension to the ALGOL 60 programming language which provides an associative memory of triples. The three items in a triple denote the association that an Attribute of an Object has a specific Value. LEAP was created by Jerome Feldman (University of California Berkeley) and Paul Rovner (MIT Lincoln Lab) in 1967. LEAP was also implemented in SAIL.

==See also==
{{div col |colwidth=15em}}
* ABC ALGOL
* [[ALGOL]]
* [[ALGOL 58]]
* [[ALGOL N]]
* [[ALGOL 68]]
* [[ALGOL W]]
* [[ALGOL X]]
* [[Atlas Autocode]]
* [[Coral 66]]
* [[Edinburgh IMP]]
* [[Jensen's Device]]
* [[ISWIM]]
* [[JOVIAL]]
* [[NELIAC]]
* [[Simula]]
* [[S-algol]]
* [[Scheme (programming language)]]
{{div col end}}

==References==
{{reflist|30em}}

===Bibliography===
{{refbegin}}
* {{cite journal
 |       journal = Communications of the ACM
 |        volume = 6
 |         issue = 1
 |          date = January 1963
 |         title = Revised Report on the Algorithmic Language Algol 60
 |        editor = Peter Naur
 |   editor-link = Peter Naur
 |         last1 = Backus
 |        first1 = John W.
 |  author-link1 = John Backus
 |         last2 = Bauer
 |        first2 = Friedrich L.
 |  author-link2 = Friedrich L. Bauer
 |         last3 = Green
 |        first3 = J.
 |         last4 = Katz
 |        first4 = C.
 |       author5 = J. McCarthy
 |  author-link5 = John McCarthy (computer scientist)
 |       author6 = P. Naur
 |  author-link6 = Peter Naur
 |       author7 = A.J. Perlis
 |  author-link7 = Alan Perlis
 |       author8 = H. Rutishauser
 |  author-link8 = Heinz Rutishauser
 |       author9 = K. Samuelson
 |      author10 = B. Vauquois
 | author-link10 = Bernard Vauquois
 |      author11 = J.H. Wegstein
 | author-link11 = Joseph Henry Wegstein
 |      author12 = A. van Wijngaarden
 | author-link12 = Adriaan van Wijngaarden
 |      author13 = M. Woodger
 | author-link13 = Mike Woodger
 |           url = https://doi.org/10.1145/366193.366201
 |     publisher = Association for Computing Machinery
 |           doi = 10.1145/366193.366201
 |         s2cid = 7853511
 |           ref = {{harvid|Naur et al.|1963}}
 }}
* {{cite book |last=Kurtz |first=Thomas E. |year=1978 |chapter=BASIC |title=History of programming languages |doi=10.1145/800025.1198404 |doi-access=free |pages=515–537 |isbn=0127450408}}
{{refend}}

==Further reading==
* {{cite tech report |last=Dijkstra |first=Edsger W. |author-link=Edsger Dijkstra |year=1961 |title="ALGOL 60 Translation: An ALGOL 60 Translator for the X1 and Making a Translator for ALGOL 60 |institution=Mathematisch Centrum |location=Amsterdam|number=35 |url=http://www.cs.utexas.edu/users/EWD/MCReps/MR35.PDF |format=PDF}}
* {{cite book |last1=Randell |first1=Brian |author1-link=Brian Randell |last2=Russell |first2=Lawford John |title=ALGOL 60 Implementation: The Translation and Use of ALGOL 60 Programs on a Computer |publisher=Academic Press |year=1964 |oclc=526731 |url=https://archive.org/details/algol60implement00rand |url-access=registration}} The design of the ''Whetstone Compiler''. One of the early published descriptions of implementing a compiler. See the related papers: [http://www.cs.ncl.ac.uk/research/pubs/articles/papers/427.pdf Whetstone Algol Revisited], and [https://web.archive.org/web/20100525044658/http://www.cs.ncl.ac.uk/publications/books/papers/124.pdf The Whetstone KDF9 ALGOL Translator] by [[Brian Randell]]
* {{cite book |title=Geschichte der deutschsprachigen Informatik - Programmiersprachen und Übersetzerbau |language=de |trans-title=History of informatics in German-speaking countries - Programming languages and compiler design |author-first=Gerhard |author-last=Goos |author-link=:de:Gerhard Goos |publisher=Fakultät für Informatik, [[Karlsruhe Institute of Technology]] (KIT) |publication-place=Karlsruhe, Germany |date=2017-08-07 |url=http://www.kps2017.uni-jena.de/proceedings/kps2017_submission_1.pdf |access-date=2022-11-14 |url-status=live |archive-url=https://web.archive.org/web/20220519131116/http://www.kps2017.uni-jena.de/proceedings/kps2017_submission_1.pdf |archive-date=2022-05-19}} (11 pages)

==External links==
* [http://www.masswerk.at/algol60/report.htm Revised Report on the Algorithmic Language ALGOL 60] by Peter Naur, et al. ALGOL definition
* A BNF [http://blackbox.userweb.mwn.de/Algol-BNF.html syntax summary] of ALGOL 60
* [https://web.archive.org/web/20111110061442/http://thor.cs.ucsb.edu/~ravenben/papers/coreos/Hoa81.pdf "The Emperor's Old Clothes"] – Hoare's 1980 ACM Turing Award speech, which discusses ALGOL history and his involvement
* [https://www.gnu.org/software/marst/ MARST], a free ALGOL-to-C translator
* [http://rogerdmoore.ca/JOUR/ An Implementation of ALGOL 60 for the FP6000] {{Webarchive|url=https://web.archive.org/web/20200725025218/http://rogerdmoore.ca/JOUR/ |date=2020-07-25}} Discussion of some implementation issues.
* {{cite journal |first=Peter |last=Naur |author-link=Peter Naur |title=The European Side of the Last Phase of the Development of ALGOL 60 |journal=ACM SIGPLAN Notices |volume=13 |issue=8 |pages=15–44 |date=August 1978 |doi=10.1145/960118.808370 |s2cid=15552479 |url=http://portal.acm.org/ft_gateway.cfm?id=808370|url-access=subscription }}
* Edinburgh University wrote compilers for Algol60 (later updated for Algol60M) based on their Atlas Autocode compilers initially bootstrapped from the Atlas to the KDF-9. The Edinburgh compilers generated code for the ICL1900, the ICL4/75 (an IBM360 clone), and the ICL2900. Here is the [http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/algolps9.txt BNF for Algol60] {{Webarchive|url=https://web.archive.org/web/20200515185211/http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/algolps9.txt |date=2020-05-15}} and the [http://history.dcs.ed.ac.uk/archive/os/emas/emas2/compilers/algol/algol60fs.imp.html ICL2900 compiler source] {{Webarchive|url=https://web.archive.org/web/20200515190532/http://history.dcs.ed.ac.uk/archive/os/emas/emas2/compilers/algol/algol60fs.imp.html |date=2020-05-15}}, [http://history.dcs.ed.ac.uk/archive/os/emas/emas2/compilers/algol/bsyslib.txt-view.html library documentation] {{Webarchive|url=https://web.archive.org/web/20200515190530/http://history.dcs.ed.ac.uk/archive/os/emas/emas2/compilers/algol/bsyslib.txt-view.html |date=2020-05-15}}, and [http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/ a considerable test suite] {{Webarchive|url=https://web.archive.org/web/20200515175751/http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/ |date=2020-05-15}} including [http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/wichtests_pete1.txt Brian Wichmann's tests.] {{Webarchive|url=https://web.archive.org/web/20200515185136/http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/wichtests_pete1.txt |date=2020-05-15}} Also there is a rather superficial [http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/palgcons.txt Algol60 to Atlas Autocode source-level translator] {{Webarchive|url=https://web.archive.org/web/20200515185142/http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/palgcons.txt |date=2020-05-15}}.
* [[Eric S. Raymond]]'s [http://www.catb.org/retro/ Retrocomputing Museum], among others a link to the NASE ALGOL 60 interpreter written in C.
* [http://www.bertnase.de/a60 The NASE interpreter]
* Stories of the B5000 and People Who Were There: a dedicated ALGOL computer [http://ed-thelen.org/comp-hist/B5000-AlgolRWaychoff.html], [http://archive.computerhistory.org/resources/text/Knuth_Don_X4100/PDF_index/k-8-pdf/k-8-u2779-B5000-People.pdf]
* {{cite report |last=Bottenbruch |first=Hermann |year=1961 |title=Structure and Use of ALGOL 60 |doi=10.2172/4020495 |osti=4020495 |url=https://digital.library.unt.edu/ark:/67531/metadc871723/|doi-access=free }}
* [http://www.softwarepreservation.org/projects/ALGOL/source/numal NUMAL] A Library of Numerical Procedures in ALGOL 60 developed at The Stichting Centrum Wiskunde & Informatica ([[legal successor (organization)|legal successor]] of Stichting Mathematisch Centrum) [https://web.archive.org/web/20101005121036/http://www.cwi.nl/en/general/Address legal owner].
* [http://www.algol60.org ALGOL 60 resources: translators, documentation, programs]
* [https://docs.racket-lang.org/algol60/ ALGOL 60] included in Racket

{{ALGOL programming}}
{{ISO standards}}
{{Authority control}}

{{DEFAULTSORT:Algol}}
[[Category:ALGOL 60| ]]
[[Category:Algol programming language family]]
[[Category:Academic programming languages]]
[[Category:Procedural programming languages]]
[[Category:Structured programming languages]]
[[Category:Systems programming languages]]
[[Category:Programming languages created in 1960]]
[[Category:Articles with example ALGOL 60 code]]
[[Category:Programming languages with an ISO standard]]