ALGOL 60


?ALGOL 60 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 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. 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.

Standardization

ALGOL 60 – with COBOL – were the first languages to seek standardization.
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 :
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

To date there have been at least 70 augmentations, extensions, derivations and sublanguages of Algol 60.
NameYearAuthorStateDescriptionTarget CPU
X1 ALGOL 60August 1960Edsger W. Dijkstra and :nl:Jaap Zonneveld|Jaap A. ZonneveldNetherlandsFirst implementation of ALGOL 60Electrologica X1
Algol1960Edgar T. IronsUSAAlgol 60CDC 1604
Burroughs Algol
1961Burroughs Corporation USABasis of the Burroughs computersBurroughs large systems
and their midrange as well.
Case ALGOL1961USASimula was originally contracted as a simulation extension of the Case ALGOLUNIVAC 1107
GOGOL1961William M. McKeemanUSAFor ODIN time-sharing systemPDP-1
DASK ALGOL1961Peter Naur, Jørn JensenDenmarkAlgol 60DASK at Regnecentralen
SMIL ALGOL1962Torgil Ekman, Carl-Erik FröbergSwedenAlgol 60SMIL at Lund University
GIER ALGOL1962Peter Naur, Jørn JensenDenmarkAlgol 60GIER at Regnecentralen
Dartmouth ALGOL 301962Thomas Eugene Kurtz et al.USALGP-30
Alcor Mainz 20021962Ursula Hill-Samelson, Hans LangmaackGermanySiemens 2002
USS 90 Algol1962L. PetroneItaly-
Elliott ALGOL1962C. A. R. HoareUKDiscussed in his 1980 Turing Award lectureElliott 803 & the Elliott 503
Algol 601962Roland StrobelEast GermanyImplemented by the Institute for Applied Mathematics, German Academy of Sciences at BerlinZeiss-Rechenautomat ZRA 1
Algol Translator1962G. van der Mey and W.L. van der PoelNetherlandsStaatsbedrijf der Posterijen, Telegrafie en TelefonieZEBRA
Kidsgrove Algol1963F. G. DuncanUKEnglish Electric Company KDF9
VALGOL1963Val SchorreUSAA test of the META II compiler compiler-
FP6000 Algol1963Roger MooreCanadawritten for Saskatchewan Power CorpFP6000
Whetstone1964Brian Randell and Lawford John RussellUKAtomic Power Division of English Electric Company. Precursor to Ferranti Pegasus, National Physical Laboratories ACE and English Electric DEUCE implementations.English Electric Company KDF9
NU ALGOL1965NorwayUNIVAC
ALGEK1965USSRMinsk-22АЛГЭК, based on ALGOL-60 and COBOL support, for economical tasks
MALGOL1966publ. A. Viil, M Kotli & M. Rakhendi,Estonian SSRMinsk-22-
ALGAMS1967GAMS group, cooperation of Comecon Academies of ScienceComeconMinsk-22, later ES EVM, BESM-
ALGOL/ZAM1967PolandPolish ZAM computer
1972ChinaChinese characters, expressed via the Symbol system-
DG/L1972USADG Eclipse family of Computers
1990Erik SchoenfelderGermanyInterpreterLinux and MS Windows
2000Andrew MakhorinRussiaAlgol-60 to C translatorAll 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.

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 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. Think of passing a pointer to swap in to a function. Now that every time swap is referenced, it's reevaluated. Say i := 1 and A := 2, so every time swap is referenced it'll return the other combination of the values. 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.

Standard operators

Examples and portability issues

Code sample comparisons

ALGOL 60

procedure Absmax Size: Result: Subscripts:;
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 > y then
begin y := abs;
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,££L??'
B := SIN'
C := COS'
PRINT,,,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 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;
EBCDIC ARRAY E;
REPLACE E BY "HELLO WORLD!";
WRITE;
END.
A simpler program using an inline format:
BEGIN
FILE F;
WRITE;
END.
An even simpler program using the Display statement:
BEGIN DISPLAY 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 The standard Elliott 803 used 5-hole paper tape and thus only had upper case. The code lacked any quote characters so £ was used for open quote and ? for close quote. Special sequences were placed in double quotes.
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 %.
'PROGRAM'
'BEGIN'
'COMMENT' OPEN QUOTE IS , PRINTABLE SPACE HAS TO
BE WRITTEN AS % BECAUSE SPACES ARE IGNORED;
WRITE TEXT;
'END'
'FINISH'