ALGOL

ALGOL was developed jointly by a committee of European and American computer scientists in a meeting in 1958 at the Swiss Federal Institute of Technology in Zurich (cf. ALGOL 58).{{Cite web |title=History of ALGOL — Software Preservation Group |url=https://www.softwarepreservation.org/projects/ALGOL/ |access-date=2024-03-14 |website=www.softwarepreservation.org}} It specified three different syntaxes: a reference syntax, a publication syntax, and an implementation syntax, syntaxes that 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; commercial applications were 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.

File:Algol&Fortran family-by-Borkowski.svg and COBOL programming language dynasty]]

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.{{cite journal |last=Knuth |first=Donald E. |year=1964 |title=Backus Normal Form vs Backus Naur Form |journal=Communications of the ACM |volume=7 |issue=12 |pages=735–736 |doi=10.1145/355588.365140|s2cid=47537431 |doi-access=free }}

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."[http://awards.acm.org/citation.cfm?id=1024454&srt=all&aw=140&ao=AMTURING&yr=2005 ACM Award Citation: Peter Naur] {{webarchive|url=https://wayback.archive-it.org/all/20120402220529/http://amturing.acm.org/award_winners/naur_1024454.cfm |date=2 April 2012}}, 2005

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

• 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 US).

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."{{Cite book |last=Perlis |first=Alan J |chapter=The American side of the development of ALGOL |date=1978 |title=History of programming languages |chapter-url=https://dl.acm.org/doi/pdf/10.1145/800025.1198352 |url=https://en.wikipedia.org/wiki/Association_for_Computing_Machinery |pages=75–91 |doi=10.1145/800025.1198352 |isbn=0-12-745040-8 |via=dl.acm.org}}

A significant contribution of the ALGOL 58 Report was to provide standard terms for programming concepts: statement, declaration, type, label, primary, block, and others.{{cite web |last1=Bemer |first1=Bob |title=A Politico-Social History of Algol |url=https://www.softwarepreservation.org/projects/ALGOL/paper/Bemer-Politico_Social_History_of_Algol.pdf |website=Computer History Museum |access-date=August 9, 2024}}

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."[http://www.eecs.umich.edu/~bchandra/courses/papers/Hoare_Hints.pdf "Hints on Programming Language Design"] {{webarchive|url=https://web.archive.org/web/20090915033339/http://www.eecs.umich.edu/~bchandra/courses/papers/Hoare_Hints.pdf |date=15 September 2009}}, 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.) 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.{{cite web |editor-last=Rees |editor-first=Jonathan |editor2-last=Clinger |editor2-first=William |editor3-last=Abelson |editor3-first=Hal |editor3-link=Hal Abelson |last=Dybvig |first=R. K. |title=Revised(3) Report on the Algorithmic Language Scheme, (Dedicated to the Memory of ALGOL 60) |url=http://groups.csail.mit.edu/mac/ftpdir/scheme-reports/r3rs-html/r3rs_toc.html |access-date=20 October 2009 | display-authors=etal |url-status=live |archive-url=https://web.archive.org/web/20100114060759/http://groups.csail.mit.edu/mac/ftpdir/scheme-reports/r3rs-html/r3rs_toc.html |archive-date=14 January 2010 | df=dmy-all}}

{{more citations needed section|date = February 2024}}

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.{{cite book |last1=Aho |first1=Alfred V. |author-link=Alfred V. Aho |last2=Sethi |first2=Ravi |author2-link=Ravi Sethi |last3=Ullman |first3=Jeffrey D. |author3-link=Jeffrey Ullman |title=Compilers: Principles, Techniques, and Tools |year=1986 |edition=1st |publisher=Addison-Wesley |isbn=0-201-10194-7}}, 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 is reevaluated. Say i := 1 and A[i] := 2, so every time swap is referenced it will 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 68 was defined using a two-level grammar formalism invented by 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.

{{expand section | with = further annotation indicating sources of code samples, as Wikipedia disallows presentation of individual editor creations or other original research | small = no |date=February 2024}}

(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 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

Here is an example of how to produce a table using Elliott 803 ALGOL.[http://www.billp.org/ccs/A104/ "803 ALGOL"] {{webarchive|url=https://web.archive.org/web/20100529063048/http://www.billp.org/ccs/A104/ |date=29 May 2010}}, the manual for 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 {{abbr|PUNCH(3)|sends output to the teleprinter rather than the tape punch.}},££L??'

B := SIN(A)'

C := COS(A)'

PRINT PUNCH(3),{{abbr|SAMELINE|suppresses the carriage return + line feed normally printed between arguments.}},{{abbr|ALIGNED(1,6)|controls the format of the output with one digit before and six after the decimal point.}},A,B,C'

END

END'

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

)

The variations and lack of portability of the programs from one implementation to another is easily demonstrated by the classic hello world program.{{citation needed|date = February 2024}}

{{main|ALGOL 58}}

ALGOL 58 had no I/O facilities.

{{main|ALGOL 60}}

Since ALGOL 60 had no I/O facilities, there is no portable hello world program in ALGOL.

The next three examples are in Burroughs Extended Algol. The first two direct output at the interactive terminal they are run on. The first uses a character array, similar to C. The language allows the array identifier to be used as a pointer to the array, and hence in a REPLACE statement.

{{sxhl|2=m2|1=

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:

{{sxhl|2=m2|1=

BEGIN

FILE F(KIND=REMOTE);

WRITE(F, <"HELLO WORLD!">);

END.

}}

An even simpler program using the Display statement. Note that its output would end up at the system console ('SPO'):

{{sxhl|2=m2|1= BEGIN DISPLAY("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 {{color box|rgba(255,255,255,0)|border=silver|‘}} and {{color box|rgba(255,255,255,0)|border=silver|’}}.

{{sxhl|2=pascal|1=

program HiFolks;

begin

print ‘Hello world’

end;

}}

Below is a version from Elliott 803 Algol (A104). The standard Elliott 803 used five-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).

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. The open and close quote characters were represented using '(' and ')' and spaces by %.{{cite web|url=http://www.icl1900.co.uk/techpub/tp3340.djvu|title=ICL 1900 series: Algol Language|publisher=ICL Technical Publication 3340|year=1965}}

'BEGIN'

WRITE TEXT('('HELLO%WORLD')');

'END'

{{main|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".

{{Contains special characters

| alt = Decimal Exponent Symbol

| link = http://mailcom.com/unicode/DecimalExponent.ttf

| special = Unicode 6.0 "[https://www.unicode.org/charts/PDF/U2300.pdf Miscellaneous Technical]" characters

| fix = Unicode#External_links

| characters = something like "₁₀" ([http://mailcom.com/unicode/DecimalExponent.ttf 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 unsupported 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 \/.[http://www.bobbemer.com/BACSLASH.HTM How ASCII Got Its Backslash] {{webarchive|url=https://web.archive.org/web/20140711225835/http://bobbemer.com/BACSLASH.HTM |date=11 July 2014}}, Bob Bemer

1962: ALCOR – This character set included the unusual "᛭" runic cross[https://www.fileformat.info/info/unicode/char/16ed/ iron/runic cross] character for multiplication and the "⏨" Decimal Exponent Symbol[http://mailcom.com/unicode/DecimalExponent.ttf Decimal Exponent Symbol] for floating point notation.{{cite journal |last=Baumann |first=R. |title=ALGOL Manual of the ALCOR Group, Part 1 |journal=Elektronische Rechenanlagen |date=October 1961 |pages=206–212 |language=de|trans-title=ALGOL Manual of the ALCOR Group}}{{cite journal |last=Baumann |first=R. |title=ALGOL Manual of the ALCOR Group, Part 2 |journal=Elektronische Rechenanlagen |volume=6 |date=December 1961 |pages=259–265 |language=de|trans-title=ALGOL Manual of the ALCOR Group}}{{cite journal |last=Baumann |first=R. |title=ALGOL Manual of the ALCOR Group, Part 3 |journal=Elektronische Rechenanlagen |volume=2 |date=April 1962 |language=de|trans-title=ALGOL Manual of the ALCOR Group}}

1964: GOST – The 1964 Soviet standard GOST 10859 allowed the encoding of 4-bit, 5-bit, 6-bit and 7-bit characters in ALGOL.{{cite web|title=GOST 10859 standard |url=http://homepages.cwi.nl/~dik/english/codes/stand.html#gost10859 |access-date=5 June 2007 |archive-url=https://web.archive.org/web/20070616201227/http://homepages.cwi.nl/~dik/english/codes/stand.html |archive-date=16 June 2007 |url-status=dead}}

1968: The "Algol 68 Report" – used extant ALGOL characters, and further adopted →, ↓, ↑, □, ⌊, ⌈, ⎩, ⎧, ○, ⊥, and ¢ characters which can be found on the IBM 2741 keyboard with typeball (or golf ball) print heads inserted (such as the APL golf ball). 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) for floating point notation was added to Unicode 5.2 for backward compatibility with historic Buran programme ALGOL software.{{cite web

|url = https://www.unicode.org/L2/L2008/08030r-subscript10.pdf

|title = Revised proposal to encode the decimal exponent symbol

|last = Broukhis

|first = Leonid

|date = 22 January 2008

|website = www.unicode.org

|publisher = ISO/IEC JTC 1/SC 2/WG 2

|access-date = 24 January 2016

|quote = 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.

|url-status = live

|archive-url = https://web.archive.org/web/20150731024347/http://www.unicode.org/L2/L2008/08030r-subscript10.pdf

|archive-date=31 July 2015

}}

To date there have been at least 70 augmentations, extensions, derivations and sublanguages of Algol 60.{{cite web|url=http://hopl.murdoch.edu.au/showlanguage.prx?exp=1807 |title=The Encyclopedia of Computer Languages |access-date=20 January 2012 |url-status=dead |archive-url=https://web.archive.org/web/20110927014141/http://hopl.murdoch.edu.au/showlanguage.prx?exp=1807 |archive-date=27 September 2011 |df=dmy}}

The Burroughs dialects included special Bootstrapping dialects such as ESPOL and NEWP. The latter is still used for Unisys MCP system software.

{{div col|content=

• Address (programming language)
• Atlas Autocode
• Coral 66
• Edinburgh IMP
• ISWIM
• JOVIAL
• NELIAC
• Simula
• S-algol
• Scheme (programming language)

}}

{{reflist|30em}}

• {{cite book |author=Randell, Brian & L. J. Russell |date=1964 |title=ALGOL 60 Implementation: The Translation and Use of ALGOL 60 Programs on a Computer |location= |publisher=Academic Press |citeseerx=10.1.1.737.475 |url=http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.737.475&rep=rep1&type=pdf |access-date=}}. On the design of the Whetstone Compiler, and one of the early published descriptions of implementing a compiler.
• {{cite web |first=E. W |last=Dijkstra |title=ALGOL 60 Translation: An ALGOL 60 Translator for the X1 and Making a Translator for ALGOL 60 |series=report MR 35/61 |publisher=Mathematisch Centrum |place=Amsterdam |year=1961 |url=http://www.cs.utexas.edu/users/EWD/MCReps/MR35.PDF |archive-url=https://ghostarchive.org/archive/20221009/http://www.cs.utexas.edu/users/EWD/MCReps/MR35.PDF |archive-date=2022-10-09 |url-status=live}}
• {{cite web |first=Frans E.J. |last=Kruseman Aretz |title=The Dijkstra–Zonneveld ALGOL 60 Compiler for the Electrologica X1 |series=Historical note SEN, 2 |place=Amsterdam: Centrum voor Wiskunde en Informatica |url=https://ir.cwi.nl/pub/4155/04155D.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://ir.cwi.nl/pub/4155/04155D.pdf |archive-date=2022-10-09 |url-status=live}}

• [http://www.masswerk.at/algol60/report.htm Revised Report on the Algorithmic Language Algol 60 by Peter Naur, et al.]
• [http://portal.acm.org/ft_gateway.cfm?id=808370&type=pdf&coll=&dl=ACM&CFID=15151515&CFTOKEN=6184618 The European Side of the Last Phase of the Development of ALGOL 60, by Peter Naur]
• [http://www.softwarepreservation.org/projects/ALGOL/ A History of ALGOL] from the Computer History Museum

{{ALGOL programming}}

{{Authority control}}

{{DEFAULTSORT:Algol}}

Category:ALGOL 60 dialect

Category:Articles with example ALGOL 60 code

Category:Computer-related introductions in 1958

Category:Procedural programming languages

Category:Programming languages created in 1958

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