|Paradigm||procedural, imperative, structured|
|Designed by||Backus, Bauer, Green, Katz, McCarthy, Naur, Perlis, Rutishauser, Samelson, van Wijngaarden, Vauquois, Wegstein, Woodger|
|Most subsequent imperative languages (so-called ALGOL-like languages), e.g. Simula, CPL, Pascal, Ada, C|
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
end pairs for delimiting them. ALGOL 60 was the first language implementing nested function definitions with lexical scope. It gave rise to many other programming languages, including CPL, Simula, BCPL, B, Pascal and C.
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.
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 (now withdrawn)
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."
The following people attended the meeting in Paris (from January 11 to 16):
- Friedrich L. Bauer, Peter Naur, Heinz Rutishauser, Klaus Samelson, Bernard Vauquois, Adriaan van Wijngaarden, and Michael Woodger (from Europe)
- John W. Backus, Julien Green, Charles Katz, John McCarthy, Alan J. 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.
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." 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.
ALGOL 60 implementations timeline
|X1 ALGOL 60||August 1960||Edsger W. Dijkstra and Jaap A. Zonneveld||Netherlands||First implementation of ALGOL 60||Electrologica X1|
|Algol||1960||Edgar T. Irons||USA||Algol 60||CDC 1604|
|Burroughs Algol |
|1961||Burroughs Corporation (with participation by Hoare, Dijkstra, and others)||USA||Basis of the Burroughs (and now Unisys MCP based) computers|| Burroughs large systems |
and their midrange as well.
|Case ALGOL||1961||USA||Simula was originally contracted as a simulation extension of the Case ALGOL||UNIVAC 1107|
|GOGOL||1961||William McKeeman||USA||For ODIN time-sharing system||PDP-1|
|DASK ALGOL||1961||Peter Naur, Jørn Jensen||Denmark||Algol 60||DASK at Regnecentralen|
|SMIL ALGOL||1962||Torgil Ekman, Carl-Erik Fröberg||Sweden||Algol 60||SMIL at Lund University|
|GIER ALGOL||1962||Peter Naur, Jørn Jensen||Denmark||Algol 60||GIER at Regnecentralen|
|Dartmouth ALGOL 30||1962||Thomas Eugene Kurtz et al.||USA||LGP-30|
|USS 90 Algol||1962||L. Petrone||Italy|
|Elliott ALGOL||1962||C. A. R. Hoare||UK||Discussed in his 1980 Turing Award lecture||Elliott 803 & the Elliott 503|
|Algol Translator||1962||G. van der Mey and W.L. van der Poel||Netherlands||Staatsbedrijf der Posterijen, Telegrafie en Telefonie||ZEBRA|
|Kidsgrove Algol||1963||F. G. Duncan||UK||English Electric Company KDF9|
|VALGOL||1963||Val Schorre||USA||A test of the META II compiler compiler|
|FP6000 Algol||1963||Roger Moore||Canada||written for Saskatchewan Power Corp||FP6000|
|Whetstone||1964||Brian Randell and Lawford John Russell||UK||Atomic Power Division of English Electric Company. Precursor to Ferranti Pegasus, National Physical Laboratories ACE and English Electric DEUCE implementations.||English Electric Company KDF9|
|ALGEK||1965||USSR||Minsk-22||АЛГЭК, based on ALGOL-60 and COBOL support, for economical tasks|
|MALGOL||1966||publ. A. Viil, M Kotli & M. Rakhendi,||Estonian SSR||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||Poland||Polish ZAM computer|
|Chinese Algol||1972||China||Chinese characters, expressed via the Symbol system|
|DG/L||1972||USA||DG Eclipse family of Computers|
|NASE||1990||Erik Schoenfelder||Germany||Interpreter||Linux and MS Windows|
|MARST||2000||Andrew Makhorin||Russia||Algol-60 to C translator||All CPUs supported by the GNU Compiler Collection; MARST is part of the GNU project|
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 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. 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.
ALGOL 60 Reserved words and restricted identifiers
There are 35 such reserved words in the standard Burroughs large systems sub-language:
There are 71 such restricted identifiers in the standard Burroughs large systems sub-language:
and also the names of all the intrinsic functions.
|second||×, / (real), ÷ (integer)|
|second||<, ≤, =, ≥, >, ≠|
Examples and portability issues
Code sample comparisons
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; 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:
FLOATING POINT ALGOL TEST' BEGIN REAL A,B,C,D' READ D' FOR A:= 0.0 STEP D UNTIL 6.3 DO BEGIN PRINT PUNCH(3),££L??' B := SIN(A)' C := COS(A)' PRINT PUNCH(3),SAMELINE,ALIGNED(1,6),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 at the University of Michigan-Dearborn Computer and Information Science Department Hello world! ALGOL Example Program page.
BEGIN FILE F(KIND=REMOTE); EBCDIC ARRAY E[0:11]; REPLACE E BY "HELLO WORLD!"; WRITE(F, *, E); END.
A simpler program using an inline format:
BEGIN FILE F(KIND=REMOTE); WRITE(F, <"HELLO WORLD!">); END.
An even simpler program using the Display statement:
BEGIN DISPLAY("HELLO WORLD!") END.
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 £ (UK 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).
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 %.
'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'
- Knuth, Donald E. (December 1964). "Backus normal Form vs Backus Naur Form". Comm. ACM. 7 (12): 735–6. doi:10.1145/355588.365140.
- ACM Award Citation / Peter Naur, 2005
- Hoare, C.A.R. (December 1973). "Hints on Programming Language Design" (PDF). p. 27. (This statement is sometimes erroneously attributed to Edsger W. Dijkstra, also involved in implementing the first ALGOL 60 compiler.)
- 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)". Retrieved 2009-10-20.
- The Encyclopedia of Computer Languages Archived September 27, 2011, at the Wayback Machine.
- Daylight, E. G. (2011). "Dijkstra's Rallying Cry for Generalization: the Advent of the Recursive Procedure, late 1950s — early 1960s". The Computer Journal. doi:10.1093/comjnl/bxr002.
- Kruseman Aretz, F.E.J. (30 June 2003). "The Dijkstra-Zonneveld ALGOL 60 compiler for the Electrologica X1". Software Engineering (PDF). History of Computer Science. Kruislaan 413, 1098 SJ Amsterdam: Centrum Wiskunde & Informatica.
- Irons, Edgar T., A syntax directed compiler for ALGOL 60, Communications of the ACM, Vol. 4, p. 51. (Jan. 1961)
- Aho, Alfred V.; Ravi Sethi; Jeffrey D. Ullman (1986). Compilers: Principles, Techniques, and Tools (1st ed.). Addison-Wesley. ISBN 0-201-10194-7., Section 7.5, and references therein
- "803 ALGOL", the manual for Elliott 803 ALGOL
- "ICL 1900 series: Algol Language". ICL Technical Publication 3340. 1965.
- Dijkstra, Edsger W. (1961). "ALGOL 60 Translation: An ALGOL 60 Translator for the X1 and Making a Translator for ALGOL 60 (PDF) (Technical report). Amsterdam: Mathematisch Centrum. 35.
- Randell, Brian; Russell, Lawford John (1964). ALGOL 60 Implementation: The Translation and Use of ALGOL 60 Programs on a Computer. Academic Press. OCLC 526731. The design of the Whetstone Compiler. One of the early published descriptions of implementing a compiler. See the related papers: Whetstone Algol Revisited, and The Whetstone KDF9 Algol Translator by Brian Randell
- Revised Report on the Algorithmic Language Algol 60 by Peter Naur, et al. ALGOL definition
- A BNF syntax summary of ALGOL 60
- "The Emperor's Old Clothes" – Hoare's 1980 ACM Turing Award speech, which discusses ALGOL history and his involvement
- MARST, a free Algol-to-C translator
- AN IMPLEMENTATION OF ALGOL 60 FOR THE FP6000 Discussion of some implementation issues.
- Naur, Peter (August 1978). "The European Side of the Last Phase of the Development of ALGOL 60". ACM SIGPLAN Notices. 13 (8): 15–44. doi:10.1145/960118.808370.
- 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 BNF for Algol60 and the ICL2900 compiler source, library documentation, and a considerable test suite including Brian Wichmann's tests. Also there is a rather superficial Algol60 to Atlas Autocode source-level translator.
- Eric S. Raymond's Retrocomputing Museum, among others a link to the NASE Algol-60 interpreter written in C.
- The NASE interpreter
- Stories of the B5000 and People Who Were There: a dedicated ALGOL computer ,
- Hermann Bottenbruch. "Structure and Use of ALGOL 60". doi:10.2172/4020495.
- NUMAL A Library of Numerical Procedures in ALGOL 60 developed at The Stichting Centrum Wiskunde & Informatica (legal successor of Stichting Mathematisch Centrum) legal owner.
- Algol 60 resources: translators, documentation, programs