Category:ALGOL 68

From Rosetta Code

ALGOL 68
This programming language may be used to instruct a computer to perform a task.

Parameter passing methods:	By reference, By value
Type safety:	Safe
Type strength:	Soft, weak, meek, firm and strong - depending on context.
Type compatibility:	Structural
Type expression:	Explicit
Type checking:	Dynamic, Static
See Also:	ALGOL 68 on the HOPL ALGOL 68 compared to other languages

Listed below are all of the tasks on Rosetta Code which have been solved using ALGOL 68.

The main aims and principles of design of ALGOL 68:

1. Completeness and clarity of design,
2. Orthogonal design,
3. Security,
4. Efficiency:
   • Static mode checking,
   • Mode-independent parsing,
   • Independent compilation,
   • Loop optimization,
   • Representations - in minimal & larger character sets.

[edit] Resources

• ALGOL BULLETIN - March 1959 to August 1988, in 52 issues[1]
• Algol68 mailinglist - December 2008 - algol68-user AT lists.sourceforge.net[2]

FYI: There are two online manual pages:

• Algol 68G Manual - By Marcel van der Veer
• Programming Algol 68 Made Easy - Sian Leitch

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:

• www.amazon.com - Aboout $119
• barnesandnoble.com - about $40

IItA68 is a beautiful book, and makes great "bedtime" reading... Highly recommended!

[edit] Status

• 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!
  • This time code was by Marcel van der Veer, author of Algol 68 Genie

[edit] Revisions

• 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.

[edit] 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:

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

[edit] 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:

¢ bold/underline typeface ¢
mode xint = int;
xint sum sq:=0;
for i while
  sum sq≠70×70
do
  sum sq+:=i↑2
od 

'pr' quote 'pr' 
'mode' 'xint' = 'int';
'xint' sum sq:=0;
'for' i 'while'
  sum sq≠70×70
'do'
  sum sq+:=i↑2
'od' 

.PR UPPER .PR
MODE XINT = INT;
XINT sum sq:=0;
FOR i WHILE
  sum sq/=70*70
DO
  sum sq+:=i**2
OD 

.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

.PR RES .PR
mode .xint = int;
.xint sum sq:=0;
for i while
  sum sq≠70×70
do
  sum sq+:=i↑2
od 

[edit] 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:

• soft - deproceduring
• weak - dereferencing or deproceduring, yielding a name
• meek - dereferencing or deproceduring
• firm - meek, followed by uniting
• strong - firm, followed by widening, rowing or voiding

Depending on the context a MODE (type) will be coerced (widened) to another type 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:

• INT to [1]INT
• REAL to [1]REAL etc

Pointers are followed (dereferenced), For example:

• REF REF REAL to REAL

[edit] Code Specimen