Category: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: | Strong |
Type compatibility: | Structural |
Type expression: | Explicit |
Type checking: | Dynamic, Static |
Lang tag(s): | algol68 |
See Also: |
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,
- Security,
- Efficiency:
- Static mode checking,
- Mode-independent parsing,
- Independent compilation,
- Loop optimization,
- Representations - in minimal & larger character sets.
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 formal definition of Algol 68 is given by a "Two-Level" or "Van Wijngaarden" grammar.
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.
A syntax chart is available here
Resources
- ALGOL BULLETIN - March 1959 to August 1988, in 52 issues
- Algol68 mailinglist - December 2008 - algol68-user AT lists.sourceforge.net
- Algol68 group at linkedin - includes various famous compiler composers.
Books available online:
- Algol 68G Manual - By Marcel van der Veer Includes the Revised Report
- Programming Algol 68 Made Easy - by Sian Mountbatten (on softwarepreservation.org)
- 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!
Editor modes:
- Emacs mode for Algol 68 supporting syntax highlighting and context-sensitive indentation.
- Vim script providing support for syntax highlighting.
- GeSHi syntax highlighting
- VS-Code Algol 68 syntax highlighting
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
- 25th October 2011 - Jejones3141 added Soundex - the 300th ALGOL 68 code specimen.
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.
Coding style of samples, alphabets and stropping
Click "Expand" for more details.
Many 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 the main routine.
On some compilers, it may be necessary to include appropriate "job cards" or preludes 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 |
Alphabets
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.
The Manual for CMU ALGOL 68S (on softwarepreservation.org) refers to the non-bold words as being in timid face.
Examples of different program representations
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.
The official spec provided for different representations of the same
program.
Quote stropping (enclosing the bold words in single quotes)
and Point stropping (preceeding the bold words with a dot)
were used.
A variant of Point stropping called RES stropping was also defined.
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.
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.
Rutgers ALGOL 68 uses quote stropping.
Most of the samples on Rosetta Code use Upper stropping.
Examples (pragmatic comments to set the stropping regime not shown):
Algol68 as typically published
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)
'mode' 'xint' = 'int'; 'xint' sum sq:=0; 'for' i 'while' sum sq≠70×70 'do' sum sq+:=i↑2 'od' |
POINT stropping
.MODE .XINT = .INT; .XINT SUM SQ:=0; .FOR I .WHILE SUM SQ .NE 70*70 .DO SUM SQ .PLUSAB I .UP 2 .OD |
RES stropping
mode .xint = int; .xint sum sq:=0; for i while sum sq≠70×70 do sum sq+:=i↑2 od |
Upper stropping
MODE XINT = INT; XINT sum sq:=0; FOR i WHILE sum sq /= 70*70 DO sum sq PLUSAB i UP 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.
Click "Expand" for more details.
These contexts are:
N a |
Context location | Coercions available in this context | Coercion examples | ||||
---|---|---|---|---|---|---|---|
Soft | Weak | Meek | Firm | Strong | |||
S t |
Right hand side of:
Also:
|
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
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 |
F i |
|
Example:
UNION(INT,REAL) var := 1 | |||||
M e |
IF ~ THEN ... FI FROM ~ BY ~ TO ~ WHILE ~ DO ... OD etc
|
Examples:
REF REF BOOL to BOOL
REF REF REF INT to INT | |||||
W e |
|
Examples:
REF BOOL to REF BOOL
REF REF INT to REF INT
REF REF REF REAL to REF REAL
REF REF REF REF STRUCT to REF STRUCT | |||||
S o |
The LHS of assignments, as "~" in: ~ := ... |
Example:
|
For more details about Primaries and Secondaries refer to Operator precedence.
See also
Library code used in Rosetta Code samples
Various (including the standard prelude)
Prime related
Row (array) related
L-System related
Tools
Format an upper-stropped Algol 68 source with Mediawiki markup
Implement read and include pragmatic-comments for compilers that don't support file inclusion
Subcategories
This category has the following 3 subcategories, out of 3 total.
@
- ALGOL 68 Implementations (9 P)
- ALGOL 68 User (8 P)
Pages in category "ALGOL 68"
The following 200 pages are in this category, out of 1,019 total.
(previous page) (next page)N
O
- O'Halloran numbers
- Object serialization
- Odd and square numbers
- Odd squarefree semiprimes
- Odd word problem
- Odd words
- Old lady swallowed a fly
- Old Russian measure of length
- One of n lines in a file
- One-dimensional cellular automata
- One-two primes
- Operator precedence
- Optional parameters
- Orbital elements
- Order two numerical lists
- Ordered words
- Ormiston pairs
- Overloaded operators
- Own digits power sum
P
- Padovan n-step number sequences
- Padovan sequence
- Pairs with common factors
- Palindrome dates
- Palindrome detection
- Palindromic primes
- Palindromic primes in base 16
- Pan base non-primes
- Pandigital prime
- Pangram checker
- Parse EBNF
- Parsing/RPN calculator algorithm
- Parsing/RPN to infix conversion
- Parsing/Shunting-yard algorithm
- Partial function application
- Partition an integer x into n primes
- Pascal matrix generation
- Pascal's triangle
- Pascal's triangle/Puzzle
- Pathological floating point problems
- Peano curve
- Pell numbers
- Pell's equation
- Penta-power prime seeds
- Percolation/Mean run density
- Perfect numbers
- Perfect shuffle
- Perfect totient numbers
- Periodic table
- Perlin noise
- Permutations
- Permutations by swapping
- Permutations with repetitions
- Pernicious numbers
- Phrase reversals
- Pi
- Pick random element
- Pierpont primes
- Piprimes
- Pisano period
- Playing cards
- Plot coordinate pairs
- Pointers and references
- Polymorphic copy
- Polymorphism
- Polynomial derivative
- Polynomial long division
- Polynomial regression
- Population count
- Positive decimal integers with the digit 1 occurring exactly twice
- Power set
- Practical numbers
- Pragmatic directives
- Price fraction
- Primality by trial division
- Primality by Wilson's theorem
- Prime conspiracy
- Prime decomposition
- Prime numbers p for which the sum of primes less than or equal to p is prime
- Prime numbers which contain 123
- Prime numbers whose neighboring pairs are tetraprimes
- Prime reciprocal sum
- Prime triangle
- Prime triplets
- Prime words
- Primes which contain only one odd digit
- Primes whose first and last number is 3
- Primes whose sum of digits is 25
- Primes with digits in nondecreasing order
- Primes: n*2^m+1
- Print itself
- Probabilistic choice
- Problem of Apollonius
- Product of divisors
- Product of min and max prime factors
- Program name
- Program termination
- Proper divisors
- Pseudo-random numbers/Middle-square method
- Pseudo-random numbers/PCG32
- Pseudo-random numbers/Splitmix64
- Pseudo-random numbers/Xorshift star
- Pythagorean quadruples
- Pythagorean triples
Q
R
- Radical of an integer
- Ramanujan primes
- Ramer-Douglas-Peucker line simplification
- Random Latin squares
- Random number generator (included)
- Random numbers
- Random sentence from book
- Range consolidation
- Range expansion
- Range extraction
- Ranking methods
- Rare numbers
- Ray-casting algorithm
- Read a file line by line
- Read a specific line from a file
- Read entire file
- Real constants and functions
- Reduced row echelon form
- Regular expressions
- Remove duplicate elements
- Remove lines from a file
- Remove vowels from a string
- Rename a file
- Rep-string
- Repeat
- Repeat a string
- Repunit primes
- Return multiple values
- Reverse a string
- Reverse words in a string
- Rhonda numbers
- Rice coding
- Riordan numbers
- Rock-paper-scissors
- Rodrigues’ rotation formula
- Roman numerals/Decode
- Roman numerals/Encode
- Roots of a function
- Roots of a quadratic function
- Roots of unity
- Rosetta Code/Rank languages by popularity
- Rot-13
- Round-robin tournament schedule
- RPG attributes generator
- RSA code
- Run-length encoding
- Runge-Kutta method
- Runtime evaluation
- Runtime evaluation/In an environment
- Ruth-Aaron numbers
S
- S-expressions
- Safe and Sophie Germain primes
- Safe primes and unsafe primes
- Sattolo cycle
- Scope modifiers
- Scope/Function names and labels
- Search a list
- Search a list of records
- SEDOLs
- Selective file copy
- Selectively replace multiple instances of a character within a string
- Self numbers
- Self-describing numbers
- Self-hosting compiler
- Semiprime
- Semordnilap
- SEND + MORE = MONEY
- Separate the house number from the street name
- Sequence of non-squares
- Sequence of primes by trial division
- Sequence of primorial primes
- Sequence: nth number with exactly n divisors
- Sequence: smallest number greater than previous term with exactly n divisors
- Sequence: smallest number with exactly n divisors
- Set
- Seven-sided dice from five-sided dice
- Shell one-liner
- Shift list elements to left by 3
- Shoelace formula for polygonal area
- Short-circuit evaluation
- Shortest common supersequence
- Show ASCII table
- Show the (decimal) value of a number of 1s appended with a 3, then squared
- Sierpinski arrowhead curve
- Sierpinski carpet
- Sierpinski square curve