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ALGOL 60

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Template:Short description Template:About Template:Infobox programming language 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 (which was first introduced by any programming languageTemplate:Clarify), 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.

StandardizationEdit

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 (now withdrawn)

HistoryEdit

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.<ref>Template:Cite journal</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">ACM Award Citation / Peter Naur, 2005</ref>

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 include recursion. It was inserted into the specification at the last minute, against the wishes of some of the committee.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</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>{{#invoke:citation/CS1|citation |CitationClass=web }} (This statement is sometimes erroneously attributed to Edsger W. Dijkstra, also involved in implementing the first ALGOL 60 compiler.)</ref><ref name="r3rs">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

ALGOL 60 implementations timelineEdit

To date there have been at least 70 augmentations, extensions, derivations and sublanguages of ALGOL 60.<ref>The Encyclopedia of Computer Languages Template:Webarchive</ref>

Name Year Author State Description Target CPU
X1 ALGOL 60 August 1960<ref>Template:Cite journal</ref> Edsger W. Dijkstra and Jaap A. Zonneveld Template:Flag First implementation of ALGOL 60<ref>Template:Cite book</ref> Electrologica X1
Algol 1960<ref>Irons, Edgar T., A syntax directed compiler for ALGOL 60, Communications of the ACM, Vol. 4, p. 51. (Jan. 1961)</ref> Edgar T. Irons Template:Flag ALGOL 60 CDC 1604
Burroughs Algol
(Several variants)		 1961 Burroughs Corporation (with participation by Hoare, Dijkstra, and others) Template:Flag Basis of the Burroughs (and now Unisys MCP based) computers Burroughs Large Systems
and midrange systems
Case ALGOL 1961 Template:Flag Simula was originally contracted as a simulation extension of the Case ALGOL UNIVAC 1107
GOGOL 1961 William M. McKeeman Template:Flag For ODIN time-sharing system PDP-1
DASK ALGOL 1961 Peter Naur, Jørn Jensen Template:Flag ALGOL 60 DASK at Regnecentralen
SMIL ALGOL 1962 Torgil Ekman, Carl-Erik Fröberg Template:Flag ALGOL 60 SMIL at Lund University
GIER ALGOL 1962 Peter Naur, Jørn Jensen Template:Flag ALGOL 60 GIER at Regnecentralen
Dartmouth ALGOL 30Template:Sfn 1962 Thomas Eugene Kurtz, Stephen J. Garland, Robert F. Hargraves, Anthony W. Knapp, Jorge LLacer Template:Flag ALGOL 60 LGP-30
Alcor Mainz 2002 1962 Ursula Hill-Samelson, Hans Langmaack Template:Flag Siemens 2002
ALCOR-Illinois 7090 1962
<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> 		Manfred Paul, Hans Rüdiger Wiehle, David Gries, and Rudolf Bayer Template:Flag, Template:Flag ALGOL 60
Implemented at Illinois and the TH München, 1962-1964 		IBM 7090
USS 90 Algol 1962 L. Petrone Template:Flag
Elliott ALGOL 1962 C. A. R. Hoare Template:Flag Discussed in his 1980 Turing Award lecture Elliott 803 & the Elliott 503
ALGOL 60 1962 Roland Strobel<ref>Rechenautomaten mit Trommelspeicher, Förderverein der Technischen Sammlung Dresden</ref> Template:Flag 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>Template:Cite journal</ref> Template:Flag 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 W.L. van der Poel Template:Flag Staatsbedrijf der Posterijen, Telegrafie en Telefonie ZEBRA
Kidsgrove Algol 1963 F. G. Duncan Template:Flag English Electric Company KDF9
SCALPTemplate:Sfn 1963 Stephen J. Garland, Anthony W. Knapp, Thomas Eugene Kurtz Template:Flag Self-Contained ALgol Processor for a subset of ALGOL 60 LGP-30
VALGOL 1963 Val Schorre Template:Flag A test of the META II compiler compiler
FP6000 Algol 1963 Roger Moore Template:Flag written for Saskatchewan Power Corp FP6000
Whetstone 1964 Brian Randell and Lawford John Russell Template:Flag 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<ref>Template:Cite thesis</ref> Template:Flag Template:Ill IBM 7090
ALGOL-GENIUS 1964 Börje Langefors Template:Flag Added COBOL-inspired data records and I/O Datasaab D-21
ALGOL 60 1965 Template:Ill<ref>Template:Cite conference</ref> Template:Flag Centre de calcul de la Faculté des Sciences de Nancy IBM 1620
Dartmouth ALGOL 1965 Stephen J. Garland, Sarr Blumson, Ron Martin Template:Flag ALGOL 60 Dartmouth Time-Sharing System for the GE 235
NU ALGOL 1965 Template:Flag UNIVAC
ALGOL 60 1965<ref>Template:Cite book</ref> F.E.J. Kruseman Aretz Template:Flag MC compiler for the EL-X8 Electrologica X8
ALGEK 1965 Template:Flag Minsk-22 АЛГЭК, based on ALGOL 60 and COBOL support, for economical tasks
MALGOL 1966 publ. A. Viil, M Kotli & M. Rakhendi, Template:Flag 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 Template:Flag Polish ZAM computer
Chinese Algol 1972 Template:Flag Chinese characters, expressed via the Symbol system
DG/L 1972 Template:Flag DG Eclipse family of Computers
NASE 1990 Erik Schoenfelder Template:Flag Interpreter Linux and MS Windows
MARST 2000 Andrew Makhorin Template:Flag 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 ESPOL and NEWP.

PropertiesEdit

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 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>Template:Cite book, 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 "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 levelsEdit

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>Template:Harvnb </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>Template:Harvnb: (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>

  1. Reserved words
  2. Stropping

ALGOL 60 Reserved words and restricted identifiersEdit

There are 24 reserved words in the Modified Report:

Template:Div col

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

Template:Div col endThere are 35 such reserved words in the standard Burroughs Large Systems sub-language:

Template:Div col

  • 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

Template:Div col end

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

  • 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

Template:Div col end

and also the names of all the intrinsic functions.

Standard operatorsEdit

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

Examples and portability issuesEdit

Code sample comparisonsEdit

ALGOL 60Edit

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 designating it as a special keyword.

Following is an example of how to produce a table using Elliott 803 ALGOL:<ref>"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 Template:Abbr,££L??'
   B := SIN(A)'
   C := COS(A)'
   PRINT Template:Abbr,Template:Abbr,Template:Abbr,A,B,C'
 END'
 END'

ALGOL 60 familyEdit

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>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> at the University of Michigan-Dearborn Computer and Information Science Department Hello world! ALGOL Example Program page.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</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: Template:Sxhl An even simpler program using the Display statement:

Template:Sxhl

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 Template:Color box and Template:Color box. Template:Sxhl 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>{{#invoke:citation/CS1|citation |CitationClass=web }}</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'

LEAPEdit

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 alsoEdit

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ReferencesEdit

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BibliographyEdit

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Further readingEdit

External linksEdit

Template:ALGOL programming Template:ISO standards Template:Authority control

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