Category:ALGOL 68: Difference between revisions
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ALGOL 68 (short for ALGOrithmic Language 1968) is an [[imperative programming|imperative]] computer programming language that was conceived as a successor to the ALGOL 60 programming language, designed with the goal of a much wider scope of application and more rigorously defined syntax and semantics.
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#* Loop optimization,
#* Representations - in minimal & larger character sets.
<br><br>▼
==Execute an ALGOL 68 program online==
* http://www.compileonline.com/execute_algol_online.php
* Algol 68G is available as one of the languages at https://tio.run
==Tasks not implemented in ALGOL 68==
[[Tasks not implemented in ALGOL 68]]
==Grammar==
The
This specifies much more than "just" the syntax and includes such semantic details as the requirement of identifiers to be declared, the necessary type checking and coercions to be applied, etc. The degree of precision allowed by the grammar came at the cost of increased complexity relative to Backus Naur Form, which was used to define [[ALGOL 60]]. It is recomended that less formal material (such as the books mentioned under "Resources" below) be consulted before delving into the Revised Report.
<br>
<br>
==Resources==
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<br>
'''Books available online''':
* [http://jmvdveer.home.xs4all.nl/
* [http://www.softwarepreservation.org/projects/ALGOL/book/pame.2008.a4.pdf/view Programming Algol 68 Made Easy - by Sian Mountbatten (on softwarepreservation.org)]
* [http://www.softwarepreservation.org/projects/ALGOL/book/Lindsey_van_der_Meulen-IItA68-Revised.pdf/view Informal Introduction to Algol 68 - by C. H. Lindsey & S. V. Van der Meulen (on softwarepreservation.org)] - if you prefer (and find) a hardcopy, be sure to get the 1977 edition. Highly recomended!
<br>
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* [http://www.vim.org/scripts/script.php?script_id=1927 Vim script] providing support for syntax highlighting.
* [http://qbnz.com/highlighter/demo.php GeSHi syntax highlighting]
* [https://marketplace.visualstudio.com/items?itemName=jlguenego.algol68 VS-Code Algol 68 syntax highlighting]
==Status==
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*Dec. 1968: Report on the Algorithmic Language ALGOL 68 - Offprint from Numerische Mathematik, 14, 79-218 (1969); Springer-Verlag. - Edited by: A. van Wijngaarden, B.J. Mailloux, J.E.L. Peck and C.H.A. Koster.
*Sep 1973: Revised Report on the Algorithmic Language Algol 68 - Springer-Verlag 1976 - Edited by: A. van Wijngaarden, B.J. Mailloux, J.E.L. Peck, C.H.A. Koster, M. Sintzoff, C.H. Lindsey, L.G.L.T. Meertens and R.G. Fisker.
==Coding style of samples, alphabets and stropping==
Click "Expand" for more details.
<div class="mw-collapsible mw-collapsed" style="width:
<div class="mw-collapsible-content" style="padding-left:2em;">
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On some compilers, it may be necessary to include appropriate "job cards"
or
not too much else is required. Examples:
{|border="1" style="border-collapse: collapse; border: 5px double grey;" align="center"
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FINISH
|}
<br><br>'''Alphabets'''
<br><br>
Notionally, Algol 68 source is written in two alphabets. The reserved words, mode indicants (type names) and operators that are non-symbolic (.e.g. '''and''', '''or''', ...) are generally referred to as "bold words" and usually shown in a bold font in literature. Words that are identifiers (used for "variable" names, procedure names, structure member names, ...) are in a separate, non-bold font.<br>
The [https://www.softwarepreservation.org/projects/ALGOL/manual/a68s.txt/view Manual for CMU ALGOL 68S (on softwarepreservation.org)] refers to the non-bold words as being in timid face.
<br><br>'''Examples of different program representations'''
<br><br>
At the time when ALGOL 68 was defined some predominant computers had
24 or 36 bit words, with 6 bit character sets. Hence it was desirable that
ALGOL 68 should be able to run on machines with only uppercase.
As multiple fonts were generally unavailable, a method of identifying the bold words was required.<br>
The official spec provided for different representations of the same
program.
and Point stropping (preceeding the bold words with a dot)
were used.<br>
In RES stropping some language-defined bold words are not preceded by a dot.
A pragmatic comment may have been required to indicate which
stropping convention was to be used, as in some of the examples below.<br>
Upper stropping (representing the bold words by upper case and
non-bold words in lower case) was introduced by Algol 68R.
Upper stropping is used by Algol 68RS and is one of the options for Algol 68G.<br>
Rutgers ALGOL 68 uses quote stropping.
Most of the samples on Rosetta Code use Upper stropping.<br><br>
Examples (pragmatic comments to set the stropping regime not shown):
{|border="1" style="border-collapse: collapse; border:
|| Algol68 as typically published
'''mode''' '''xint''' = '''int''';
'''xint''' sum sq:=0;
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sum sq+:=i↑2
'''od'''
||
'mode' 'xint' = 'int';
'xint' sum sq:=0;
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sum sq+:=i↑2
'od'
|| POINT stropping
.MODE .XINT = .INT;
.XINT SUM SQ:=0;
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.OD
|| RES stropping
mode .xint = int;
.xint sum sq:=0;
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od
|| Upper stropping
MODE XINT = INT;
XINT sum sq:=0;
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<br>
Click "Expand" for more details.
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g
||Right hand side of:
* Identity-declarations, as "~" in: <
* Initialisations, as "~" in: <
Also:
* Actual-parameters of calls, as "~" in:<
* Enclosed clauses of casts, as "~" in: <
* Units of routine-texts
* Statements yielding VOID
* All parts (but one) of a balanced clause
* One side of an identity relation, as "~" in: <
|bgcolor=aaaaff rowspan=4 width="50px"| deproc- eduring
|bgcolor=aaeeaa rowspan=3 width="50px"| all '''soft''' then weak deref- erencing
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|colspan=1 bgcolor=ffcccc|
Widening occurs if there is no loss of precision. For example: An INT will be coerced to a REAL, and a REAL will be coerced to a LONG REAL. But not vice-versa. Examples:
<
INT to REAL
REAL to COMPL
BITS to []BOOL
BYTES to STRING</
A variable can also be coerced (rowed) to an array of length 1.
For example:
<
REAL to [1]REAL</
|-
!F<br>
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m
||
*Operands of formulas as "~" in:<
*Parameters of transput calls
|colspan=3 bgcolor=ffcc99| Example:
<
|-
!M<br>
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* Trimscripts (yielding INT)
* Enquiries: e.g. as "~" in the following
<
<
* Primaries of calls (e.g. sin in sin(x))
|colspan=4 bgcolor=ffee99|Examples:
<
REF REF REF INT to INT</
|-
!W<br>
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k
||
* Primaries of slices, as in "~" in: <
* Secondaries of selections, as "~" in: <
|colspan=5 bgcolor=aaeeaa|Examples:
<
REF REF INT to REF INT
REF REF REF REAL to REF REAL
REF REF REF REF STRUCT to REF STRUCT</
|-
!S<br>
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f<br>
t
|| The LHS of assignments, as "~" in: <
|colspan=6 bgcolor=aaaaff| Example:
* deproceduring of: <
|}
For more details about Primaries and Secondaries refer to [[Operator_precedence#ALGOL_68|Operator precedence]].
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== Library code used in Rosetta Code samples ==
[https://rosettacode.org/wiki/
[https://rosettacode.org/wiki/Category:ALGOL_68-primes Prime related]<br/>
▲<br>
[https://rosettacode.org/wiki/Category:ALGOL_68-rows Row (array) related]<br/>
[https://rosettacode.org/wiki/Category:ALGOL_68-l-system L-System related]
== Tools ==
[[Syntax_highlighting_using_Mediawiki_formatting#ALGOL 68|Format an upper-stropped Algol 68 source with Mediawiki markup]]<br/>
[[Compiler/Simple_file_inclusion_pre_processor#ALGOL 68|Implement ''read'' and ''include'' pragmatic-comments for compilers that don't support file inclusion]]
{{language programming paradigm|Concurrent}}
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