This programming language may be used to instruct a computer to perform a task.
|Parameter passing methods:||By reference, By value|
|Type strength:||Soft, weak, meek, firm and strong - depending on context.|
|Type checking:||Dynamic, Static|
If you know ALGOL 68, please write code for some of the tasks not implemented in ALGOL 68.
ALGOL 68 (short for ALGOrithmic Language 1968) is an 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.
The main aims and principles of design of ALGOL 68:
- Completeness and clarity of design,
- Orthogonal design,
- Static mode checking,
- Mode-independent parsing,
- Independent compilation,
- Loop optimization,
- Representations - in minimal & larger character sets.
 Execute an ALGOL 68 program online
- Van Wijngaarden grammar: 
- Backus–Naur Form/Yacc: 
- Syntax Chart (Size 516.6 kB - File type application/pdf)
- ALGOL BULLETIN - March 1959 to August 1988, in 52 issues
- Algol68 mailinglist - December 2008 - algol68-user AT lists.sourceforge.net
- Algol68 group at linked:  - includes various famous compiler composers.
FYI: There are two online manual pages:
Or - if you prefer a hardcopy - you can try and pick up a hard cover manual like "Informal Introduction to Algol 68" - by C. H. Lindsey & S. V. Vander Meulen. Be sure to get the 1977 edition:
IItA68 is a beautiful book, and makes great "bedtime" reading... Highly recommended!
- NEW: softwarepreservation.org has an on-line IItA68 PDF ready for download.
- Emacs mode for Algol 68 supporting syntax highlighting and context-sensitive indentation.
- Vim script providing support for syntax highlighting.
- NEW: GeSHi syntax highlighting
- 20th December 1968 - ALGOL 68's Final Report was ratified by UNESCO's IFIP working group 2.1 in Munich.
- 20th December 2008 - Zig Zag - the 100th ALGOL 68 code contribution on rosettacode.org!
- Happy 40th Birthday ALGOL 68,
- AND 50th Birthday ALGOL 58.
- 23rd August 2009 - algol68g-1.18.0-9h released
- 20th December 2009 - Happy 51st/41st Birthdays with Hamming numbers - the 200th ALGOL 68 code contribution on rosettacode.org!
- 25th October 2011 - Jejones3141 added Soundex - the 300th ALGOL 68 code specimen.
- Mar. 1968: Draft Report on the Algorithmic Language ALGOL 68 - Edited by: A. van Wijngaarden, B.J. Mailloux, J.E.L. Peck and C.H.A. Koster.
- Oct. 1968: Penultimate Draft Report on the Algorithmic Language ALGOL 68 - Chapters 1-9 - Edited by: A. van Wijngaarden, B.J. Mailloux, J.E.L. Peck and C.H.A. Koster.
- 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.
 Code samples
Most of the code samples provided here have a leading
main:( and a matching
) at the end. These are not actually required in the language, but are included so as to highlight that the code sample is complete, and works with (at least) ALGOL 68G unmodified.
On some compilers, it may be necessary to include appropriate "job cards" or precludes in order for the programs to compile successfully. Hopefully not too much else is required. Examples:
|Brief Algol68||Algol68 as in rosettacode||Actual ELLA Algol 68RS code|
print(("Hello, world!",new line))
main:( print(("Hello, world!",new line)) )
PROGRAM helloworld CONTEXT VOID USE standard BEGIN print(("Hello, world!", new line)) END FINISH
 Example of different program representations
At the time when ALGOL 68 was defined some predominant computers had 36 bit words, and 6 bit character sets. Hence it was desirable that ALGOL 68 should be able to run on machines with only uppercase. Hence the official spec provided for different representations of the same program. Example:
| Algol68 as typically published
¢ bold/underline typeface ¢ mode xint = int; xint sum sq:=0; for i while sum sq≠70×70 do sum sq+:=i↑2 od
| quote stropping (similar to wiki)
'pr' quote 'pr' 'mode' 'xint' = 'int'; 'xint' sum sq:=0; 'for' i 'while' sum sq≠70×70 'do' sum sq+:=i↑2 'od'
| Code for a 7-bit/ascii compiler
.PR UPPER .PR MODE XINT = INT; XINT sum sq:=0; FOR i WHILE sum sq/=70*70 DO sum sq+:=i**2 OD
| Code for a 6-bits/byte compiler
.PR POINT .PR .MODE .XINT = .INT; .XINT SUM SQ:=0; .FOR I .WHILE SUM SQ .NE 70*70 .DO SUM SQ .PLUSAB I .UP 2 .OD
| Algol68 using RES stropping
.PR RES .PR mode .xint = int; .xint sum sq:=0; for i while sum sq≠70×70 do sum sq+:=i↑2 od
 Coercion (casting)
ALGOL 68 has a hierarchy of contexts which determine which kind of coercions are available at a particular point in the program. These contexts are:
|Context location||Coercions available in this context||Coercion examples|
|Right hand side of:
|deproc- eduring||all soft then weak deref- erencing||all weak then deref- erencing||all meek then uniting||all firm then widening, rowing and voiding||
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 LONG INT
A variable can also be coerced (rowed) to an array of length 1.
INT to INTetc
UNION(INT,REAL) var := 1
IF ~ THEN ... FIand
FROM ~ BY ~ TO ~ WHILE ~ DO ... OD etc
REF REF BOOL to BOOL
REF BOOL to REF BOOL
| The LHS of assignments, as "~" in:
~ := ...
For more details about Primaries and Secondaries refer to Operator precedence.
 Code Specimen
This category has the following 3 subcategories, out of 3 total.
Pages in category "ALGOL 68"
The following 351 pages are in this category, out of 351 total.