ALGOL

{{otherusesof|Algol}}
{{Mergefrom|ALGOL object code|date=June 2007}}
{{Infobox programming language
| name = [[ALGOL|ALGOL]]
| logo =
| paradigm = [[procedural programming|procedural]], [[Imperative programming language|imperative]], [[structured programming|structured]]
| year = [[1958]]
| designer = Designed by committee
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| influenced_by =
| influenced = [[PASCAL|PASCAL]], [[Ada (programming language)|ADA]], [[Scheme (programming language)|Scheme]]
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'''ALGOL''' (short for '''ALGO'''rithmic '''L'''anguage) is a family of [[imperative programming|imperative]] [[computer programming|computer]] [[programming language]]s originally developed in the mid [[1950s]] which greatly influenced many other languages, and became the ''de facto'' way [[algorithms]] were described in text-books and academic works for almost the next 30 years. It was designed to avoid some of the perceived problems with [[FORTRAN]]  and eventually gave rise to many other programming languages (including [[Pascal (programming language)|Pascal]]). ALGOL uses bracketed statement blocks and was the first language to use '''begin''' '''end''' pairs for delimiting them. Fragments of ALGOL-like syntax are sometimes still used as a notation for algorithms, so-called [[Pidgin Algol]].

There are three official main branches of ALGOL family:
* [[ALGOL 58]] - originally known as the '''IAL''' (for '''I'''nternational '''A'''lgorithmic '''L'''anguage.)
* '''ALGOL 60''' - revised 1963 <ref>{{cite web|title=Revised Report on the Algorithmic Language Algol 60|year=1963|url=http://www.masswerk.at/algol60/report.htm|accessyear=2007|accessmonthday=Jun 8}}</ref>
* [[ALGOL 68]] - revised 1973 <ref>{{cite web|title=Revised Report on the Algorithmic Language ALGOL 68|year=1973|url=http://burks.brighton.ac.uk/burks/language/other/a68rr/rrtoc.htm|accessyear=2007|accessmonthday=Jun 8}}</ref>

[[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.

==History==
ALGOL was developed jointly by a committee of European and American computer scientists in a meeting in 1958 at [[ETH Zurich]]. 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. 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 the suggestion by [[Donald Knuth]]
<ref>Knuth, Donald E. (1964) Backus Normal Form vs. Backus Naur Form. Communications of the ACM 7(12):735-736</ref> renamed to [[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 1 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 (computer scientist)|Julien Green]], [[Charles Katz]], [[John McCarthy (computer scientist)|John McCarthy]], [[Alan Perlis|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.” 
Both John Backus and Peter Naur served on the committee which created ALGOL 60, as did [[Wally Feurzeig]] who later created [[Logo programming language|Logo]].

ALGOL 60 inspired many languages that followed it. [[C.A.R. 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>[http://www.eecs.umich.edu/~bchandra/courses/papers/Hoare_Hints.pdf “Hints on Programming Language Design”], C.A.R. Hoare, December 1973. Page 27. (This statement is sometimes erroneously attributed to [[Edsger Dijkstra]], also involved in implementing the first ALGOL 60 [[compiler]].)</ref>

===True ALGOL 60s specification and implementation timeline===
{{cleanup-section|date=July 2007}}
There were about 70 augmented, extensions, derivations and sublanguages of Algol 60[http://hopl.murdoch.edu.au/showlanguage.prx?exp=1807]

{|class="wikitable" border="1" style="border-collapse: collapse;"
|-
!|Name
!|Year
!|Author
!|State
!|Description
!|Target CPU
!|Licencing
|-
|[[Elliott ALGOL]]|| 1960 || [[C. A. R. Hoare]] || UK || Subject of the famous [[Turing]] lecture|| [[National-Elliott]] 803 & the Elliott 503 ||
|-
|[[Case ALGOL]]|| 1961 || || US || [[Simula]] was originally contracted as a simulation extension of the Case ALGOL || [[UNIVAC 1107]] ||
|-
|[[EMIDEC Algol]]|| 1961 || || US || || [[EMIDEC]] ||
|-
|[[GOGOL]]|| 1961 || [[Bill McKeeman]] || US || For [[ODIN]] time-sharing system || [[PDP-1]] ||
|-
|[[X1 Algol 60]]|| 1961 || [[Edsger Dijkstra]] and J.A. Zonneveld || Netherlands || Mathematical Centre, Amsterdam || [[Electrologica X1|X1]] ||
|-
|[[Dartmouth ALGOL 30]]|| 1962 || [[Thomas Eugene Kurtz]] et al || US || || [[LGP-30]] ||
|-
|[[USS 90 Algol]]|| 1962 || [[L. Petrone]]  || Italy || || ||
|-
| Algol Translator || 1962 || G. van der May and W.L. van der Poel || Netherlands || Staatsbedrijf der Posterijen, Telegrafie en Telefonie || [[ZEBRA (computer)|ZEBRA]] ||
|-
|[[Kidsgrove Algol]]|| 1963 || [[F. G. Duncan]]  || UK || || [[English Electric]] [[KDF9]] ||
|-
|[[VALGOL]]|| 1963 || [[Val Schorre]] || US || A test of the [[META II]] compiler compiler || ||
|-
|[[Whetstone]]|| 1964 || [[Brian Randell]] and L J Russell || UK || Atomic Power Division of [[English Electric]]. Precursor to Ferranti [[Pegasus (computer)]], National Physical Laboratories [[ACE (computer)]] and [[English Electric]] [[DEUCE]] implementations. || [[English Electric]] [[KDF9]] ||
|-
|[[NU ALGOL]]|| 1965 || || Norway || || [[UNIVAC]] ||
|-
|ALGEK|| 1965 || || [[USSR]] || [[Minsk family of computers|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 family of computers|Minsk-22]] || ||
|-
|[[ALGAMS]]|| 1967 || GAMS group (ГАМС, группа автоматизации программирования для машин среднего класса), cooperation of Comecon Academies of Science || [[Comecon]] || [[Minsk family of computers|Minsk-22]], later [[ES EVM]], [[BESM]] || ||
|-
|[[ALGOL/ZAM]]|| 1967 || || Poland || || Polish [[ZAM]] computer ||
|-
|[[RegneCentralen ALGOL]]|| 1967 || [[Peter Naur]] || Denmark || || ||
|-
|[[Simula 67]]|| 1967 || [[Ole-Johan Dahl]] and [[Kristen Nygaard]] || Norway || Algol 60 with classes || [[UNIVAC 1107]] ||
|-
|[[DG/L]]|| 1973 || || US || || DG [[Data General Eclipse|Eclipse]] family of computers ||
|-
|[[Chinese Algol]]|| 1974 || || China || Chinese characters, expressed via the Symbol system || ? ||
|}

The [[Burroughs large systems]] are designed to be programmed in an extended variant of ALGOL 60 known as Burroughs Extended ALGOL. Their [[operating system]], the [[MCP (Burroughs Large Systems)|MCP]], was written in [[ESPOL]], an extension of Burroughs Extended ALGOL, as far back as 1961. The [[Unisys]] Corporation still markets machines in this family today, running the MCP (now maintained in another ALGOL variant known as [[NEWP]]) and supporting ALGOL compilers which have been extended several more times.

==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 allowed for two [[evaluation strategy|evaluation strategies]] for [[Parameter (computer science)|parameter]] passing: the common call-by-value, and call-by-name. Call-by-name had certain limitations in contrast to call-by-reference, making it an undesirable feature in imperative language design. For example, it is impossible in ALGOL 60 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>
{{cite book
| last=Aho
| first=Alfred V.
| authorlink=Alfred V. Aho
| coauthors=[[Ravi Sethi]], [[Jeffrey D. Ullman]]
| title=[[Compilers: Principles, Techniques, and Tools]]
| year=1986
| edition=1st edition
| publisher=Addison-Wesley
| isbn=0-201-10194-7}}, Section 7.5, and references therein</ref>.
However, call-by-name is still beloved of ALGOL implementors for the interesting “[[thunk]]s” 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 grammar]]s 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.

== Code sample (ALGOL 60) ==
(The way the bold text has to be written depends on the implementation, e.g. 'INTEGER' (including the quotation marks) for '''integer'''.)

'''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’s an example of how to produce a table using Elliott 803 ALGOL<ref>[http://www.billp.org/ccs/A104/ “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 PUNCH(3),££L??'
B := SIN(A)'
C := COS(A)'
PRINT PUNCH(3),SAMELINE,ALIGNED(1,6),A,B,C'
END'
END'

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. 

==Timeline: Hello world==
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)===
{{main|ALGOL 58}}
ALGOL 58 had no I/O facilities.

===ALGOL 60 family===
Since ALGOL 60 had no I/O facilities, there is no portable [[Hello world program|“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 [http://www.engin.umd.umich.edu/CIS/course.des/cis400/algol/hworld.html this site].

BEGIN
FILE F(KIND=REMOTE);
EBCDIC ARRAY E[0:11];
REPLACE E BY "HELLO WORLD!";
WRITE(F, *, E);
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 ‘ and ’.

'''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).

HIFOLKS’
BEGIN
PRINT £HELLO WORLD££L??’
END’

The ICL 1900 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.
'BEGIN'
'WRITE TEXT'("HELLO WORLD");
'END'

===ALGOL 68===

{{main|ALGOL 68}}

In the language of the "Algol 68 Report", Input/output facilities were collectively called the "[[Transput]]".

'''ALGOL 68''' code was published reserved words were typically lowercase, but bolded or underlined.
begin
print(("Hello, world!",newline))
end
OR using a specific transput channel:
begin
putf((stand out,$gl$,"Hello, world!"))
end

For ease of programming on the 7-bit computers of the time there were "official" methods to "'''BOLD'''" reserved words, for example, by using uppercase:
BEGIN
print(("Hello, world!",newline))
END

Programmers were sometimes required to totally "THINK IN UPPERCASE" on computers that only had 6-bit characters, eg the [[Control Data Corporation#The CDC 6600: defining supercomputing|CDC]] "[[super computers]]". In this case the above code would be written:
'BEGIN'
PRINT(("HELLO, WORLD!",NEWLINE))
'END'

The "Algol 68 Report" was translated into Russian, German, French and Bulgarian, and allowed programming in languages with larger character sets, eg [[Cyrillic alphabet]]. eg the Russian [[BESM|BESM-4]].
BEGIN
print(("Здравствуй, мир!",newline))
END
Note: The 1964 Russian standard [[GOST|GOST 10859]] allowed the encoding of 4-bit, 5-bit, 6-bit and 7-bit characters in ALGOL
<ref>{{cite web|title=GOST 10859 standard|url=http://homepages.cwi.nl/~dik/english/codes/stand.html#gost10859|accessyear=2007|accessmonthday=Jun 5}}</ref>.

== ALGOL 60 Reserved words and restricted identifiers ==
There are 35 such reserved words in the standard [[Burroughs large systems]] sub-language: <code> 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.</code>

There are 71 such restricted identifiers in the standard [[Burroughs large systems]] sub-language: <code>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</code> and also the names of all the intrinsic functions.

==See also==
* [[ALGOL 58]]
* [[ALGOL 68]]
* [[Algol-W]]
* [[Atlas Autocode]]
* [[CORAL66]]
* [[Edinburgh IMP]]
* [[Jensen's Device]]
* [[ISWIM]]
* [[JOVIAL]]
* [[Simula]]

== Notes ==
<references/>

== References ==
* B. 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: [http://www.cs.ncl.ac.uk/research/pubs/articles/papers/427.pdf Whetstone Algol Revisited,] and [http://www.cs.ncl.ac.uk/research/pubs/trNN/papers/38.pdf The Whetstone KDF9 Algol Translator] by B. Randell
* E. W, Dijkstra, ''Algol 60 translation: an algol 60 translator for the x1 and making a translator for algol 60'', report MR 35/61. Mathematisch Centrum, Amsterdam, 1961. [http://www.cs.utexas.edu/users/EWD/MCReps/MR35.PDF]

== External links ==
* [http://www.masswerk.at/algol60/report.htm Revised Report on the Algorithmic Language Algol 60] by Peter Naur, et al. ALGOL definition
* A BNF [http://www.lrz.de/~bernhard/Algol-BNF.html syntax summary] of ALGOL 60
* [http://www.sli-institute.ac.uk/%7Ebob/hoare.pdf “The Emperor’s Old Clothes”] – Hoare’s 1980 ACM Turing Award speech, which discusses ALGOL history and his involvement
* [http://www.gnu.org/software/marst/ MARST], a free Algol-to-C translator
* [http://rogerdmoore.ca/JOUR/ AN IMPLEMENTATION OF ALGOL 60 FOR THE FP6000] Discussion of some implementation issues.
* [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]
* 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 [http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/algolps9.txt BNF for Algol60] and the [http://history.dcs.ed.ac.uk/archive/os/emas/emas2/compilers/algol/algol60fs.imp.html ICL2900 compiler source], [http://history.dcs.ed.ac.uk/archive/os/emas/emas2/compilers/algol/bsyslib.txt-view.html library documentation], and [http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/ a considerable test suite] including [http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/wichtests_pete1.txt Brian Wichmann’s tests.] Also there is a rather superficial [http://history.dcs.ed.ac.uk/archive/os/emas/users/ercc07/emas-2900/palgcons.txt Algol60 to Atlas Autocode source-level translator].
* [[Eric Raymond]]'s [http://www.catb.org/retro/ Retrocomputing Museum], among others a link to the NASE Algol-60 interpreter written in C.

[[Category:ALGOL 60 dialects]]
[[Category:Algol programming language family]]
[[Category:Articles with example ALGOL 60 code]]
[[Category:Procedural programming languages]]
[[Category:Programming languages]]
[[Category:Structured programming languages]]
[[Category:Systems programming languages]]

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