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 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 within one another (a feature introduced by ALGOL 60) with lexical scope. It gave rise to many other languages, including CPL, PL/I, Simula, BCPL, B, Pascal, and 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. 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. ISO 1538:1984 Programming languages – ALGOL 60 (stabilized) 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 (now withdrawn)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 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.
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 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, Charles Katz, 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.
Several authors of the original report met in April 1962 to resolve issues that had arisen. Their work resulted in the publication of the "Revised report on the algorithmic language ALGOL 60".
Further clarifications and the inclusion of I/O procedures were made by the Working Group 2.1 of IFIP Technical Committee 2. These efforts were published as the "Modified Report on the algorithmic language ALGOL 60" in 1975.
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." (This statement is sometimes erroneously attributed to Edsger W. Dijkstra, also involved in implementing the first ALGOL 60 compiler.)
ALGOL 60 implementations timeline To date there have been at least 70 augmentations, extensions, derivations and sublanguages of ALGOL 60.The Encyclopedia of Computer Languages
NameYearAuthorStateDescriptionTarget CPU X1 ALGOL 60 August 1960 Edsger W. Dijkstra and Jaap A. Zonneveld First implementation of ALGOL 60 Electrologica X1 Algol 1960Irons, Edgar T., A syntax directed compiler for ALGOL 60, Communications of the ACM, Vol. 4, p. 51. (Jan. 1961) Edgar T. Irons ALGOL 60 CDC 1604 Burroughs Algol(Several variants) 1961 Burroughs Corporation (with participation by Hoare, Dijkstra, and others) Basis of the Burroughs (and now Unisys MCP based) computers Burroughs Large Systemsand midrange systems Case ALGOL 1961 Simula was originally contracted as a simulation extension of the Case ALGOL UNIVAC 1107 GOGOL 1961 William M. McKeeman For ODIN time-sharing system PDP-1 DASK ALGOL 1961 Peter Naur, Jørn Jensen ALGOL 60 DASK at Regnecentralen SMIL ALGOL 1962 Torgil Ekman, Carl-Erik Fröberg ALGOL 60 SMIL at Lund University GIER ALGOL 1962 Peter Naur, Jørn Jensen ALGOL 60 GIER at Regnecentralen Dartmouth ALGOL 30 1962 Thomas Eugene Kurtz, Stephen J. Garland, Robert F. Hargraves, Anthony W. Knapp, Jorge LLacer ALGOL 60 LGP-30 Alcor Mainz 2002 1962 Ursula Hill-Samelson, Hans Langmaack Siemens 2002 ALCOR-Illinois 7090 1962 Manfred Paul, Hans Rüdiger Wiehle, David Gries, and Rudolf Bayer , ALGOL 60Implemented at Illinois and the TH München, 1962–1964 IBM 7090 USS 90 Algol 1962 L. Petrone Elliott ALGOL 1962 C. A. R. Hoare Discussed in his 1980 Turing Award lecture Elliott 803 & the Elliott 503 ALGOL 60 1962 Roland StrobelRechenautomaten mit Trommelspeicher, Förderverein der Technischen Sammlung Dresden Implemented by the Institute for Applied Mathematics, German Academy of Sciences at Berlin Zeiss-Rechenautomat ZRA 1ALGOL 601962Bernard Vauquois, Louis Bolliet Institut d'Informatique et Mathématiques Appliquées de Grenoble (IMAG) and Compagnie des Machines BullBull Gamma 60 Algol Translator 1962 G. van der Mey and W.L. van der Poel Staatsbedrijf der Posterijen, Telegrafie en Telefonie ZEBRA Kidsgrove Algol 1963 F. G. Duncan English Electric Company KDF9 SCALP 1963 Stephen J. Garland, Anthony W. Knapp, Thomas Eugene Kurtz Self-Contained ALgol Processor for a subset of ALGOL 60 LGP-30 VALGOL 1963 Val Schorre A test of the META II compiler compiler FP6000 Algol 1963 Roger Moore written for Saskatchewan Power Corp FP6000 Whetstone 1964 Brian Randell and Lawford John Russell Atomic Power Division of English Electric Company. Precursor to Ferranti Pegasus, National Physical Laboratories ACE and English Electric DEUCE implementations English Electric Company KDF9 ALGOL 60 1964 Jean-Claude Boussard IBM 7090 ALGOL-GENIUS 1964 Börje Langefors Added COBOL-inspired data records and I/O Datasaab D-21 ALGOL 60 1965 Centre de calcul de la Faculté des Sciences de Nancy IBM 1620 Dartmouth ALGOL 1965 Stephen J. Garland, Sarr Blumson, Ron Martin ALGOL 60 Dartmouth Time-Sharing System for the GE 235 NU ALGOL 1965 UNIVAC ALGOL 60 1965 F.E.J. Kruseman Aretz MC compiler for the EL-X8 Electrologica X8ALGEK 1965 Minsk-22 АЛГЭК, based on ALGOL 60 and COBOL support, for economical tasks MALGOL 1966 publ. A. Viil, M Kotli & M. Rakhendi, Minsk-22 ALGAMS 1967 GAMS group (ГАМС, группа автоматизации программирования для машин среднего класса), cooperation of Comecon Academies of Science Comecon Minsk-22, later ES EVM, BESM ALGOL/ZAM 1967 Polish ZAM computerChinese Algol 1972 Chinese characters, expressed via the Symbol system DG/L 1972 DG Eclipse family of ComputersNASE1990Erik Schoenfelder Interpreter Linux and MS WindowsMARST 2000Andrew MakhorinALGOL 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 as 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 strategies for 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 recomputes every parameter when it is used in an expression, so 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., 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'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 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 reserving some identifiers for standard functions. The Reference Language has lower case letters and other characters not available in the 6-bit character sets typical of ALGOL 60's era.
The reports briefly describe hardware representations. Implementations differ in their hardware representations of underlined independent basic symbols.: (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. Reserved words Stropping They also differ in their hardware representation of delimiters.
ALGOL 60 Reserved words and restricted identifiers There are 24 basic symbols in the Modified Report that are words in boldface. Although those words are not reserved in the reference and publication languages, some hardware implementations may reserve them. There are 24 such 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 standard Burroughs 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