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ALGOL 60

From Wikipedia, the free encyclopedia
Member of the ALGOL family of computer programming languages
This article is about the programming language. For other uses, seeAlgol (disambiguation).
ALGOL 60
Paradigmsprocedural,imperative,structured
FamilyALGOL
Designed byBackus,Bauer,Green,Katz,McCarthy,Naur,Perlis,Rutishauser,Samelson,van Wijngaarden,Vauquois,Wegstein,Woodger
First appeared1960; 65 years ago (1960)
Typing disciplineStatic,strong
ScopeLexical
Influenced by
ALGOL 58
Influenced
Most subsequent imperative languages (so-calledALGOL-like languages), e.g.,PL/I,Simula,CPL,Pascal,Ada,C

ALGOL 60 (short forAlgorithmic Language 1960) is a member of theALGOL family of computerprogramming languages. It followed on fromALGOL 58 which had introducedcode blocks and thebegin andend pairs for delimiting them, representing a key advance in the rise ofstructured programming. ALGOL 60 was one of the first languages implementing function definitions (that could be invoked recursively). ALGOL 60 function definitions could benested within one another (which was first introduced by any programming language[clarification needed]), withlexical scope. It gave rise to many other languages, includingCPL,PL/I,Simula,BCPL,B,Pascal, andC. Practically every computer of the era had asystems programming language based on ALGOL 60 concepts.

Niklaus Wirth based his ownALGOL W on ALGOL 60 before moving to developPascal. Algol-W was intended to be the next generation ALGOL but theALGOL 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

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ALGOL 60 – withCOBOL – were the first languages to seek standardization.

History

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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 standardinput/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 theBackus normal form method of describing programming languages specifically for ALGOL 58. It was revised and expanded byPeter Naur for ALGOL 60, and atDonald Knuth's suggestion renamedBackus–Naur form.[1]

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."[2]

The following people attended the meeting in Paris (from January 11 to 16):

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 includerecursion. It was inserted into the specification at the last minute, against the wishes of some of the committee.[3]

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."[4][5]

ALGOL 60 implementations timeline

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To date there have been at least 70 augmentations, extensions, derivations and sublanguages of ALGOL 60.[6]

NameYearAuthorStateDescriptionTarget CPU
X1 ALGOL 60August 1960[7]Edsger W. Dijkstra andJaap A. Zonneveld NetherlandsFirst implementation of ALGOL 60[8]Electrologica X1
Algol1960[9]Edgar T. Irons USAALGOL 60CDC 1604
Burroughs Algol
(Several variants)
1961Burroughs Corporation (with participation byHoare,Dijkstra, and others) USABasis of theBurroughs (and nowUnisysMCP based) computersBurroughs Large Systems
and midrange systems
Case ALGOL1961 USASimula was originally contracted as a simulation extension of the Case ALGOLUNIVAC 1107
GOGOL1961William M. McKeeman USAFor ODIN time-sharing systemPDP-1
DASK ALGOL1961Peter Naur,Jørn Jensen DenmarkALGOL 60DASK at Regnecentralen
SMIL ALGOL1962Torgil Ekman,Carl-Erik Fröberg SwedenALGOL 60SMIL atLund University
GIER ALGOL1962Peter Naur,Jørn Jensen DenmarkALGOL 60GIER at Regnecentralen
Dartmouth ALGOL 30[10]1962Thomas Eugene Kurtz,Stephen J. Garland, Robert F. Hargraves,Anthony W. Knapp,Jorge LLacer USAALGOL 60LGP-30
Alcor Mainz 20021962Ursula Hill-Samelson, Hans Langmaack GermanySiemens 2002
ALCOR-Illinois 70901962
[11][12]
Manfred Paul, Hans Rüdiger Wiehle,David Gries, andRudolf Bayer USA, West GermanyALGOL 60
Implemented atIllinois and theTH München, 1962-1964
IBM 7090
USS 90 Algol1962L. Petrone Italy
Elliott ALGOL1962C. A. R. Hoare UKDiscussed in his 1980Turing Award lectureElliott 803 & the Elliott 503
ALGOL 601962Roland Strobel[13] East GermanyImplemented by the Institute for Applied Mathematics,German Academy of Sciences at BerlinZeiss-Rechenautomat ZRA 1
ALGOL 601962Bernard Vauquois, Louis Bolliet[14] FranceInstitut d'Informatique et Mathématiques Appliquées de Grenoble (IMAG) and Compagnie des Machines BullBull Gamma 60
Algol Translator1962G. van der Mey andW.L. van der Poel NetherlandsStaatsbedrijf der Posterijen, Telegrafie en TelefonieZEBRA
Kidsgrove Algol1963F. G. Duncan UKEnglish Electric CompanyKDF9
SCALP[15]1963Stephen J. Garland,Anthony W. Knapp,Thomas Eugene Kurtz USASelf-Contained ALgol Processor for a subset of ALGOL 60LGP-30
VALGOL1963Val Schorre USAA test of theMETA II compiler compiler
FP6000 Algol1963Roger Moore Canadawritten forSaskatchewan Power CorpFP6000
Whetstone1964Brian Randell and Lawford John Russell UKAtomic Power Division of English Electric Company. Precursor toFerranti Pegasus, National Physical LaboratoriesACE andEnglish Electric DEUCE implementationsEnglish Electric CompanyKDF9
ALGOL 601964Jean-Claude Boussard[16] FranceInstitut d'informatique et mathématiques appliquées de Grenoble [fr]IBM 7090
ALGOL-GENIUS1964Börje Langefors SwedenAddedCOBOL-inspired data records and I/ODatasaab D-21
ALGOL 601965Claude Pair [fr][17] FranceCentre de calcul de la Faculté des Sciences de NancyIBM 1620
Dartmouth ALGOL1965Stephen J. Garland, Sarr Blumson, Ron Martin USAALGOL 60Dartmouth Time-Sharing System for theGE 235
NU ALGOL1965 NorwayUNIVAC
ALGOL 601965[18]F.E.J. Kruseman Aretz NetherlandsMC compiler for the EL-X8Electrologica X8
ALGEK1965 Soviet UnionMinsk-22АЛГЭК, based on ALGOL 60 andCOBOL support, for economical tasks
MALGOL1966publ. A. Viil, M Kotli & M. Rakhendi, Estonian SSRMinsk-22
ALGAMS1967GAMS group (ГАМС, группа автоматизации программирования для машин среднего класса), cooperation of Comecon Academies of ScienceComeconMinsk-22, laterES EVM,BESM
ALGOL/ZAM1967 PolandPolishZAM computer
Chinese Algol1972 ChinaChinese characters, expressed via the Symbol system
DG/L1972 USADGEclipse family of Computers
NASE1990Erik Schoenfelder GermanyInterpreterLinux and MS Windows
MARST2000Andrew Makhorin RussiaALGOL 60 to C translatorAll CPUs supported by the GNU Compiler Collection; MARST is part of the GNU project

The Burroughs dialects included special system programming dialects such asESPOL andNEWP.

Properties

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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 oftransput (ALGOL 68 parlance for input/output) facilities.

ALGOL 60 provided twoevaluation strategies forparameter passing: the commoncall-by-value, andcall-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 tocall-by-reference. For example, without specifying the parameters asvalue orreference, 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.[19] 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 "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.

Language levels

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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[20] reserving some identifiers for standard functions.

The reports briefly describe hardware representations. Implementations differ in their hardware representations of underlined independent basic symbols[21]

  1. Reserved words
  2. Stropping

ALGOL 60 Reserved words and restricted identifiers

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There are 24 reserved words in the Modified Report:

  • ARRAY
  • BEGIN
  • BOOLEAN
  • COMMENT
  • DO
  • ELSE
  • END
  • FALSE
  • FOR
  • GOTO
  • IF
  • INTEGER
  • LABEL
  • OWN
  • PROCEDURE
  • REAL
  • STEP
  • STRING
  • SWITCH
  • THEN
  • TRUE
  • UNTIL
  • VALUE
  • WHILE

There are 35 such reserved words in the standardBurroughs Large Systems sub-language:

  • ALPHA
  • ARRAY
  • BEGIN
  • BOOLEAN
  • COMMENT
  • CONTINUE
  • DIRECT
  • DO
  • DOUBLE
  • ELSE
  • END
  • EVENT
  • FALSE
  • FILE
  • FOR
  • FORMAT
  • GO
  • IF
  • INTEGER
  • LABEL
  • LIST
  • LONG
  • OWN
  • POINTER
  • PROCEDURE
  • REAL
  • STEP
  • SWITCH
  • TASK
  • THEN
  • TRUE
  • UNTIL
  • VALUE
  • WHILE
  • ZIP

There are 71 such restricted identifiers in the standard Burroughs Large Systems sub-language:

  • ACCEPT
  • AND
  • ATTACH
  • BY
  • CALL
  • CASE
  • CAUSE
  • CLOSE
  • DEALLOCATE
  • DEFINE
  • DETACH
  • DISABLE
  • DISPLAY
  • DIV
  • DUMP
  • ENABLE
  • EQL
  • EQV
  • EXCHANGE
  • EXTERNAL
  • FILL
  • FORWARD
  • GEQ
  • GTR
  • IMP
  • IN
  • INTERRUPT
  • IS
  • LB
  • LEQ
  • LIBERATE
  • LINE
  • LOCK
  • LSS
  • MERGE
  • MOD
  • MONITOR
  • MUX
  • NEQ
  • NO
  • NOT
  • ON
  • OPEN
  • OR
  • OUT
  • PICTURE
  • PROCESS
  • PROCURE
  • PROGRAMDUMP
  • RB
  • READ
  • RELEASE
  • REPLACE
  • RESET
  • RESIZE
  • REWIND
  • RUN
  • SCAN
  • SEEK
  • SET
  • SKIP
  • SORT
  • SPACE
  • SWAP
  • THRU
  • TIMES
  • TO
  • WAIT
  • WHEN
  • WITH
  • WRITE

and also the names of all the intrinsic functions.

Standard operators

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PriorityOperator
first arithmeticfirst↑ (power)
second×, / (real), ÷ (integer)
third+, -
second<, ≤, =, ≥, >, ≠
third¬ (not)
fourth∧ (and)
fifth∨ (or)
sixth⊃ (implication)
seventh≡ (equivalence)

Examples and portability issues

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Code sample comparisons

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ALGOL 60

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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;begininteger p, q;    y := 0; i := k := 1;for p := 1step 1until ndofor q := 1step 1until mdoif abs(a[p, q]) > ythenbegin y := abs(a[p, q]);                    i := p; k := qendend 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 ofinteger, above, therebydesignating it as a special keyword.

Following is an example of how to produce a table usingElliott 803 ALGOL:[22]

 FLOATING POINT ALGOL TEST' BEGIN REAL A,B,C,D' READ D' FOR A:= 0.0 STEP D UNTIL 6.3 DO BEGIN   PRINTPUNCH(3),££L??'   B := SIN(A)'   C := COS(A)'   PRINTPUNCH(3),SAMELINE,ALIGNED(1,6),A,B,C' END' END'

ALGOL 60 family

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Since ALGOL 60 had no I/O facilities, there is no portablehello 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[23] at theUniversity of Michigan-Dearborn Computer and InformationScience Department Hello world! ALGOL Example Program page.[24]

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.[25]

A simpler program using an inline format:

BEGINFILEF(KIND=REMOTE);WRITE(F,<"HELLO WORLD!">);END.

An even simpler program using the Display statement:

BEGINDISPLAY("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   and  .

programHiFolks;beginprintHelloworldend;

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'

TheICT 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 %.[26]

  '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

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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

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References

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  1. ^Knuth, Donald E. (December 1964)."Backus normal Form vs Backus Naur Form".Communications of the ACM.7 (12):735–6.doi:10.1145/355588.365140.S2CID 47537431.
  2. ^ACM Award Citation / Peter Naur, 2005
  3. ^van Emden, Maarten (2014)."How recursion got into programming: a tale of intrigue, betrayal, and advanced programming-language semantics".A Programmer's Place.
  4. ^Hoare, C.A.R. (December 1973)."Hints on Programming Language Design"(PDF). p. 27. (This statement is sometimes erroneously attributed toEdsger W. Dijkstra, also involved in implementing the first ALGOL 60compiler.)
  5. ^Abelson, Hal;Dybvig, R. K.; et al. Rees, Jonathan; Clinger, William (eds.)."Revised(3) Report on the Algorithmic Language Scheme (Dedicated to the Memory of ALGOL 60)". Retrieved2009-10-20.
  6. ^The Encyclopedia of Computer LanguagesArchived September 27, 2011, at theWayback Machine
  7. ^Daylight, E. G. (2011)."Dijkstra's Rallying Cry for Generalization: the Advent of the Recursive Procedure, late 1950s – early 1960s".The Computer Journal.54 (11):1756–1772.doi:10.1093/comjnl/bxr002.
  8. ^Kruseman Aretz, F.E.J. (30 June 2003)."The Dijkstra-Zonneveld ALGOL 60 compiler for the Electrologica X1"(PDF).Software Engineering. History of Computer Science. Amsterdam: Centrum Wiskunde & Informatica.ISSN 1386-3711. Archived fromthe original(PDF) on 2004-01-17.
  9. ^Irons, Edgar T., A syntax directed compiler for ALGOL 60, Communications of the ACM, Vol. 4, p. 51. (Jan. 1961)
  10. ^Kurtz 1978.
  11. ^Gries, D.; Paul, M.; Wiehle, H. R (1965)."Some techniques used in the ALCOR Illinois 7090".Communications of the ACM.8 (8):496–500.doi:10.1145/365474.365511.S2CID 18365024.
  12. ^Bayer, R.; Gries, D.; Paul, M.; Wiehle, H. R. (1967)."The ALCOR Illinois 7090/7094 post mortem dump".Communications of the ACM.10 (12):804–808.doi:10.1145/363848.363866.S2CID 3783605.
  13. ^Rechenautomaten mit Trommelspeicher, Förderverein der Technischen Sammlung Dresden
  14. ^Mounier-Kuhn, Pierre (2014)."Algol in France: From Universal Project to Embedded Culture".IEEE Annals of the History of Computing.36 (4):6–25.doi:10.1109/MAHC.2014.50.ISSN 1058-6180.
  15. ^Kurtz 1978, p. 517.
  16. ^Boussard, Jean-Claude (June 1964).Etude et réalisation d'un compilateur Algol60 sur calculateur éléctronique du type IBM 7090/94 et 7040/44 [Design and implementation of a compiler Algol60 on electronic calculator IBM 7090/94 and 7040/44] (PhD) (in French). Université Joseph-Fourier - Grenoble I.
  17. ^Claude Pair (27 April 1965).Description d'un compilateur ALGOL.European Région 1620 Users Group. IBM.
  18. ^Kruseman Aretz, F.E.J. (1973).An Algol 60 compiler in Algol 60. Mathematical Centre Tracts. Amsterdam: Mathematisch Centrum.
  19. ^Aho, Alfred V.;Sethi, Ravi;Ullman, Jeffrey D. (1986).Compilers: Principles, Techniques, and Tools (1st ed.). Addison-Wesley.ISBN 978-0-201-10194-2., Section 7.5, and references therein
  20. ^Naur et al. 1963, 3.2.4. Standard functions
  21. ^Naur et al. 1963, 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.
  22. ^"803 ALGOL", the manual forElliott 803 ALGOL
  23. ^"The ALGOL Programming Language".www.engin.umd.umich.edu. Archived fromthe original on 10 February 2010. Retrieved11 January 2022.
  24. ^"Hello world! Example Program".www.engin.umd.umich.edu. Archived fromthe original on 4 February 2010. Retrieved11 January 2022.
  25. ^Fortran#"Hello, World!" example
  26. ^"ICL 1900 series: Algol Language". ICL Technical Publication 3340. 1965.

Bibliography

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Further reading

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External links

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