The Info List - ALGOL

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ALGOL (short for Algorithmic Language)[1] is a family of imperative computer programming languages, originally developed in the mid-1950s, which greatly influenced many other languages and was the standard method for algorithm description used by the ACM in textbooks and academic sources for more than thirty years.[2] In the sense that the syntax of most modern languages is "Algol-like",[3] it was arguably the most influential of the four high-level programming languages among which it was roughly contemporary: FORTRAN, Lisp, and COBOL.[4] It was designed to avoid some of the perceived problems with FORTRAN
and eventually gave rise to many other programming languages, including PL/I, Simula, BCPL, B, Pascal, and C. ALGOL introduced code blocks and the begin…end pairs for delimiting them. It was also the first language implementing nested function definitions with lexical scope. Moreover, it was the first programming language which gave detailed attention to formal language definition and through the Algol 60 Report introduced Backus–Naur form, a principal formal grammar notation for language design. There were three major specifications, named after the year they were first published:

ALGOL 58 – originally proposed to be called IAL, for International Algebraic Language. ALGOL 60 – first implemented as X1 ALGOL 60 in mid-1960. Revised 1963.[5][6] ALGOL 68
– introduced new elements including flexible arrays, slices, parallelism, operator identification. Revised 1973.[7]

Niklaus Wirth
Niklaus Wirth
based his own ALGOL W on ALGOL 60 before developing Pascal. ALGOL-W was based on the proposal for 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. ALGOL 68
is substantially different from ALGOL 60 and was not well received, so that in general "Algol" means ALGOL 60 and dialects thereof.


1 Important implementations 2 History

2.1 Algol and programming language research 2.2 IAL implementations timeline

3 Properties 4 Examples and portability issues

4.1 Code sample comparisons

4.1.1 ALGOL 60 4.1.2 ALGOL 68

4.2 Timeline: Hello world

4.2.1 ALGOL 58 (IAL) 4.2.2 ALGOL 60 family 4.2.3 ALGOL 68

4.3 Timeline of ALGOL special characters

5 See also 6 References 7 Further reading 8 External links

Important implementations[edit] The International Algebraic Language (IAL), or ALGOL 58, was extremely influential and generally considered the ancestor of most of the modern programming languages (the so-called Algol-like languages). Additionally, ALGOL object code was a simple, compact, and stack-based instruction set architecture commonly used in teaching compiler construction and other high order languages (of which Algol is generally considered the first). History[edit] ALGOL was developed jointly by a committee of European and American computer scientists in a meeting in 1958 at ETH Zurich
ETH Zurich
(cf. ALGOL 58). It specified three different syntaxes: a reference syntax, a publication syntax, and an implementation syntax. The different syntaxes permitted it to use different keyword names and conventions for decimal points (commas vs periods) for different languages. ALGOL 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 other than Burroughs Corporation. ALGOL 60 did however become the standard for the publication of algorithms and had a profound effect on future language development. John Backus
John Backus
developed the Backus normal form method of describing programming languages specifically for ALGOL 58. It was revised and expanded by Peter Naur
Peter Naur
for ALGOL 60, and at Donald Knuth's suggestion renamed Backus–Naur form.[8] 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."[9] The following people attended the meeting in Paris (from 1 to 16 January):

Friedrich L. Bauer, Peter Naur, Heinz Rutishauser, Klaus Samelson, Bernard Vauquois, Adriaan van Wijngaarden, and Michael Woodger
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." 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."[10] 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.[11] Algol and programming language research[edit] As Peter Landin
Peter Landin
noted, the language Algol was the first language to combine seamlessly imperative effects with the (call-by-name) lambda calculus. Perhaps the most elegant formulation of the language is due to John C. Reynolds, and it best exhibits its syntactic and semantic purity. Reynolds's idealized Algol also made a convincing methodological argument regarding the suitability of local effects in the context of call-by-name languages, to be contrasted with the global effects used by call-by-value languages such as ML. The conceptual integrity of the language made it one of the main objects of semantic research, along with PCF and ML.[12] IAL implementations timeline[edit] To date there have been at least 70 augmentations, extensions, derivations and sublanguages of Algol 60.[13]

Name Year Author Country Description Target CPU

ZMMD-implementation 1958 Friedrich L. Bauer, Heinz Rutishauser, Klaus Samelson, Hermann Bottenbruch Germany implementation of ALGOL 58 Z22 (later Zuse's Z23 was delivered with an Algol 60 compiler)[14]

X1 ALGOL 60 August 1960[15] Edsger W. Dijkstra
Edsger W. Dijkstra
and Jaap A. Zonneveld Netherlands First implementation of ALGOL 60[16] Electrologica X1

Elliott ALGOL 1960s C. A. R. Hoare UK Subject of the 1980 Turing lecture[17] Elliott 803, Elliott 503, Elliott 4100 series

JOVIAL 1960 Jules Schwarz USA A DOD HOL prior to Ada Various (see article)

Burroughs Algol (Several variants) 1961 Burroughs Corporation
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 Case Institute of Technology[18] USA Simula was originally contracted as a simulation extension of the Case ALGOL UNIVAC

GOGOL 1961 William M. McKeeman USA For ODIN time-sharing system[19] PDP-1

RegneCentralen ALGOL 1961 Peter Naur, Jørn Jensen Denmark Implementation of full Algol 60 DASK at Regnecentralen

Dartmouth ALGOL 30 1962 Thomas Eugene Kurtz
Thomas Eugene Kurtz
et al. USA


USS 90 Algol 1962 L. Petrone Italy

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
English Electric
Company KDF9

VALGOL 1963 Val Schorre USA A test of the META II compiler compiler

Whetstone 1964 Brian Randell and L. J. Russell UK Atomic Power Division of English Electric
English Electric
Company. Precursor to Ferranti Pegasus, National Physical Laboratories ACE and English Electric DEUCE implementations. English Electric
English Electric
Company KDF9




ALGEK 1965

USSR Minsk-22 АЛГЭК, based on ALGOL-60 and COBOL
support, for economical tasks

ALGOL W 1966 Niklaus Wirth USA Proposed successor to ALGOL 60 IBM System/360

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



Polish ZAM computer

Simula 67 1967 Ole-Johan Dahl and Kristen Nygaard Norway Algol 60 with classes UNIVAC

Chinese Algol 1972

China Chinese characters, expressed via the Symbol system

DG/L 1972


DG Eclipse family of Computers

S-algol 1979 Ron Morrison UK Addition of orthogonal datatypes with intended use as a teaching language PDP-11
with a subsequent implementation on the Java VM

The Burroughs dialects included special Bootstrapping dialects such as ESPOL and NEWP. The latter is still used for Unisys
MCP system software. Properties[edit] 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 (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.[20] Think of passing a pointer to swap(i, A[i]) in to a function. Now that every time swap is referenced, it is 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
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 68
was defined using a two-level grammar formalism invented by Adriaan van Wijngaarden
Adriaan van Wijngaarden
and which bears his name. Van Wijngaarden grammars use a context-free grammar to generate an infinite set of productions that will recognize a particular ALGOL 68
program; notably, they are able to express the kind of requirements that in many other programming language standards are labelled "semantics" and have to be expressed in ambiguity-prone natural language prose, and then implemented in compilers as ad hoc code attached to the formal language parser. Examples and portability issues[edit] Code sample comparisons[edit] ALGOL 60[edit] (The way the bold text has to be written depends on the implementation, e.g. 'INTEGER' -- quotation marks included -- for integer. This is known as stropping.)

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

Here is an example of how to produce a table using Elliott 803 ALGOL.[21]




PUNCH(3) sends output to the teleprinter rather than the tape punch. SAMELINE suppresses the carriage return + line feed normally printed between arguments. ALIGNED(1,6) controls the format of the output with 1 digit before and 6 after the decimal point. ALGOL 68[edit] The following code samples are ALGOL 68
versions of the above ALGOL 60 code samples. ALGOL 68
implementations used ALGOL 60's approaches to stropping. In ALGOL 68's case tokens with the bold typeface are reserved words, types (modes) or operators.

proc abs max = ([,]real a, ref real y, ref int i, k)real: comment The absolute greatest element of the matrix a, of size ⌈a by 2⌈a is transferred to y, and the subscripts of this element to i and k; comment begin real y := 0; i := ⌊a; k := 2⌊a; for p from ⌊a to ⌈a do for q from 2⌊a to 2⌈a do if abs a[p, q] > y then y := abs a[p, q]; i := p; k := q fi od od; y end # abs max #

Note: lower (⌊) and upper (⌈) bounds of an array, and array slicing, are directly available to the programmer.

floating point algol68 test: ( real a,b,c,d;

# printf - sends output to the file stand out. # # printf($p$); – selects a new page # printf(($pg$,"Enter d:")); read(d);

for step from 0 while a:=step*d; a <= 2*pi do printf($l$); # $l$ - selects a new line. # b := sin(a); c := cos(a); printf(($z-d.6d$,a,b,c)) # formats output with 1 digit before and 6 after the decimal point. # od )

Timeline: Hello world[edit] The variations and lack of portability of the programs from one implementation to another is easily demonstrated by the classic hello world program. ALGOL 58 (IAL)[edit] Main article: ALGOL 58 ALGOL 58 had no I/O
facilities. ALGOL 60 family[edit] Main article: ALGOL 60 Since ALGOL 60 had no I/O
facilities, there is no portable hello world program in ALGOL.


A simpler program using an inline format:


An even simpler program using the Display statement:


An alternative example, using Elliott Algol I/O
is as follows. Elliott Algol used different characters for "open-string-quote" and "close-string-quote":

program HiFolks; begin print ‘Hello world’; end;

Here is a version for the Elliott 803
Elliott 803
Algol (A104) The standard Elliott 803
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. The open and close quote characters were represented using '(' and ')' and spaces by %.[22]


ALGOL 68[edit] Main article: ALGOL 68 ALGOL 68
code was published with reserved words typically in lowercase, but bolded or underlined.

begin printf(($gl$,"Hello, world!")) end

In the language of the "Algol 68 Report" the input/output facilities were collectively called the "Transput". Timeline of ALGOL special characters[edit]

This article contains Unicode
6.0 "Miscellaneous Technical" characters. Without proper rendering support, you may see question marks, boxes, or other symbols instead of something like "₁₀" (Decimal Exponent Symbol U+23E8 TTF).

The ALGOLs were conceived at a time when character sets were diverse and evolving rapidly; also, the ALGOLs were defined so that only uppercase letters were required. 1960: IFIP – The Algol 60 language and report included several mathematical symbols which are available on modern computers and operating systems, but, unfortunately, were not supported on most computing systems at the time. For instance: ×, ÷, ≤, ≥, ≠, ¬, ∨, ∧, ⊂, ≡, ␣ and ⏨. 1961 September: ASCII – The ASCII
character set, then in an early stage of development, had the (Back slash) character added to it in order to support ALGOL's boolean operators / and /.[23] 1962: ALCOR
– This character set included the unusual "᛭" (iron/runic cross[24]) character and the "⏨" (Decimal Exponent Symbol[25]) for floating point notation.[26][27][28] 1964: GOST
– The 1964 Soviet standard GOST
10859 allowed the encoding of 4-bit, 5-bit, 6-bit and 7-bit characters in ALGOL.[29] 1968: The "Algol 68 Report" – used existing ALGOL characters, and further adopted →, ↓, ↑, □, ⌊, ⌈, ⎩, ⎧, ○, ⊥ and ¢ characters which can be found on the IBM 2741
IBM 2741
keyboard with "golf-ball" print heads inserted (such as the APL golfball). These became available in the mid-1960s while ALGOL 68
was being drafted. The report was translated into Russian, German, French and Bulgarian, and allowed programming in languages with larger character sets, e.g. Cyrillic
alphabet of the Soviet BESM-4. All ALGOL's characters are also part of the Unicode
standard and most of them are available in several popular fonts. 2009 October: Unicode
– The "⏨" (Decimal Exponent Symbol[25]) for floating point notation was added to Unicode
5.2 for backward compatibility with historic Buran (spacecraft)
Buran (spacecraft)
ALGOL software.[30] See also[edit]

Address programming language Atlas Autocode Coral 66 Edinburgh IMP Jensen's Device ISWIM

JOVIAL Tron (video game) NELIAC Simula S-algol Scheme (programming language)


^ The name of this language family is sometimes given in mixed case (Algol 60), and sometimes in all uppercase (ALGOL68). For simplicity this article uses ALGOL. ^ Collected Algorithms of the ACM Compressed archives of the algorithms. ACM. ^ O'Hearn, P. W.; Tennent, R. D. (September 1996). "Algol-like languages, Introduction". Archived from the original on 14 November 2011.  ^ "The ALGOL Programming Language", University of Michigan-Dearborn ^ Backus, J. W.; Bauer, F. L.; Green, J.; Katz, C.; McCarthy, J.; Perlis, A. J.; Rutishauser, H.; Samelson, K.; Vauquois, B.; Wegstein, J. H.; van Wijngaarden, A.; Woodger, M. (May 1960). Naur, Peter, ed. Report on the Algorithmic Language ALGOL 60. Copenhagen. doi:10.1145/367236.367262. ISSN 0001-0782.  ^ "Revised Report on the Algorithmic Language Algol 60". 1963. Archived from the original on 25 June 2007. Retrieved 8 June 2007.  ^ "Revised Report on the Algorithmic Language ALGOL 68" (PDF). 1973. Retrieved 13 September 2014.  ^ Knuth, Donald E. (1964). "Backus Normal Form vs Backus Naur Form". Communications of the ACM. 7 (12): 735–736. doi:10.1145/355588.365140.  ^ ACM Award Citation / Peter Naur, 2005 ^ "Hints on Programming Language Design", C.A.R. Hoare, December 1973. Page 27. (This statement is sometimes erroneously attributed to Edsger W. Dijkstra, also involved in implementing the first ALGOL 60 compiler.) ^ R. K. Dybvig; et al. Jonathan Rees; William Clinger Hal Abelson, eds. "Revised(3) Report on the Algorithmic Language Scheme, (Dedicated to the Memory of ALGOL 60)". Retrieved 20 October 2009.  ^ Peter O'Hearn
Peter O'Hearn
and Robert D. Tennent. 1996. Algol-Like Languages. Birkhauser Boston Inc., Cambridge, MA, USA. ^ "The Encyclopedia of Computer Languages". Archived from the original on 27 September 2011. Retrieved 20 January 2012.  ^ Computer Museum History, Historical Zuse-Computer Z23, restored by the Konrad Zuse
Konrad Zuse
Schule in Hünfeld, for the Computer Museum History Center in Mountain View (California) USA ^ Daylight, E. G. (2011). "Dijkstra's Rallying Cry for Generalization: the Advent of the Recursive Procedure, late 1950s – early 1960s". The Computer Journal. 54: 1756–1772. CiteSeerX . 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.  ^ Hoare, Antony (1980). "The Emperor's Old Clothes". Communications of the ACM. 24 (2). doi:10.1145/358549.358561.  ^ Koffman, Eliot. "All I Really Need to KnowI Learned in CS1" (PDF). Retrieved 20 May 2012.  ^ "GOGOL - PDP-1
Algol 60 (Computer Language)". Online Historical Encyclopaedia of Programming Languages. Retrieved 1 Feb 2018.  ^ 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
Elliott 803
ALGOL ^ "ICL 1900 series: Algol Language". ICL Technical Publication 3340. 1965.  ^ How ASCII
Got Its Backslash, Bob Bemer ^ https://www.fileformat.info/info/unicode/char/16ed/index.htm ^ a b http://unicode.org/charts/PDF/U2300.pdf ^ Baumann, R. (October 1961). " ALGOL Manual of the ALCOR
Group, Part 1" [ ALGOL Manual of the ALCOR
Group]. Elektronische Rechenanlagen (in German): 206–212.  access-date= requires url= (help) ^ Baumann, R. (December 1961). " ALGOL Manual of the ALCOR
Group, Part 2" [ ALGOL Manual of the ALCOR
Group]. Elektronische Rechenanlagen (in German). 6: 259–265.  access-date= requires url= (help) ^ Baumann, R. (April 1962). " ALGOL Manual of the ALCOR
Group, Part 3" [ ALGOL Manual of the ALCOR
Group]. Elektronische Rechenanlagen (in German). 2.  access-date= requires url= (help) ^ " GOST
10859 standard". Archived from the original on 16 June 2007. Retrieved 5 June 2007.  ^ Broukhis, Leonid (22 January 2008). "Revised proposal to encode the decimal exponent symbol" (PDF). www.unicode.org. ISO/IEC JTC 1/SC 2/WG 2. Retrieved 24 January 2016. This means that the need to transcode GOST-based software and documentation can still arise: legacy numerical algorithms (some of which may be of interest,e.g. for the automatic landing of the Buran shuttle …) optimized for the non-IEEE floating point representation of BESM-6 cannot be simply recompiled and be expected to work reliably, and some human intervention may be necessary. 

Further reading[edit]

F.L. Bauer, R. Baumann, M. Feliciano, K. Samelson, Introduction to Algol. Prentice Hall, 1964, ISBN 0-13-477828-6 Brian Randell and L. J. Russell, ALGOL 60 Implementation: The Translation and Use of ALGOL 60 Programs on a Computer. Academic Press, 1964. 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 Dijkstra, E. W (1961), Algol 60 translation: an algol 60 translator for the x1 and making a translator for algol 60 (PDF), report MR 35/61, Amsterdam: Mathematisch Centrum  Revised Report on the Algorithmic Language Algol 60 by Peter Naur, et al. ALGOL definition "The European Side of the Last Phase of the Development of ALGOL 60" by Peter Naur

External links[edit]

History of ALGOL at the Computer History Museum Web enabled ALGOL-F compiler for