Category:ALGOL 68: Difference between revisions
m (→Grammar: http://www.softwarepreservation.org/projects/ALGOL/book/Lindsey_van_der_Meulen-IItA68-Revised-SyntaxOnly.pdf/view) |
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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:
{|class="wikitable"
* soft - deproceduring▼
! Context name !! Coercions applied in this context !! Context location !! Coercion examples
|-
|| The LHS of assignments, as in: <lang algol68>:=</lang>
* strong - firm, followed by widening, rowing or voiding▼
||
* deproceduring of: <lang algol68>PROC REAL random: e.g. random</lang>
|-
of precision. For example: An INT will be coerced to a REAL, and a REAL will be▼
|weak || all ''soft'' above then weak dereferencing
||
* INT to REAL▼
* Primaries of slices
* REAL to COMPL▼
* Secondaries of selections, as in: <lang algol68>OF</lang>
* BITS to []BOOL▼
||
* BYTES to STRING▼
<lang algol68>REF REF REF INT to REF INT</lang>
|-
|meek
|| all ''weak'' above then dereferencing
||
* Trimscripts (yielding INT)
* Enquiries: e.g. "~" in the following<lang algol68>IF ~ THEN ... FI</lang> and <lang algol68>FROM ~ BY ~ TO ~ WHILE ~ DO ... OD etc</lang>
* Primaries of calls (e.g. sin in sin(x))
||
|-
|firm || all ''meek'' then uniting
||
*Operands of formulas
*Parameters of transput calls
|| e.g. <lang algol68>UNION(INT,REAL) var := 1</lang>
|-
||strong
||Right hand side of:
* Identity-declarations :=:
* Initialisations
Also:
* Actual-parameters of calls
* Enclosed clauses of casts
* Units of routine-texts
* Statements yielding VOID
* All parts (but one) of a balanced clause
* One side of an identity relation
▲||Widening occures 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:
<lang algol68>INT to LONG INT
A variable can also be coerced (rowed) to an array of length 1. For example:
|}
For more details about Primaries and Secondaries refer to [[Operator_precedence#ALGOL_68|Operator precedence]].
▲* REF REF REAL to REAL
== Code Specimen ==
{{language programming paradigm|Concurrent}}
|
Revision as of 11:21, 23 April 2013
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 (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
Grammar
The grammar for ALGOL 68 is officially in the two level, Van Wijngaarden grammar but a subset has been done in the one level Backus–Naur Form:
- Van Wijngaarden grammar: [1]
- Backus–Naur Form/Yacc: [2]
- Syntax Chart (Size 516.6 kB - File type application/pdf)
Resources
- ALGOL BULLETIN - March 1959 to August 1988, in 52 issues[3]
- Algol68 mailinglist - December 2008 - algol68-user AT lists.sourceforge.net[4]
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:
- www.amazon.com - Aboout $119
- barnesandnoble.com - about $40
IItA68 is a beautiful book, and makes great "bedtime" reading... Highly recommended!
Editor modes:
- Emacs mode for Algol 68 supporting syntax highlighting and context-sensitive indentation.
- Vim script providing support for syntax colouring.
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.
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 name | Coercions applied in this context | Context location | Coercion examples |
---|---|---|---|
soft | deproceduring | The LHS of assignments, as in: <lang algol68>:=</lang> |
|
weak | all soft above then weak dereferencing |
|
<lang algol68>REF REF REF INT to REF INT</lang> |
meek | all weak above then dereferencing |
|
<lang algol68>REF REF REF REAL to REAL</lang> |
firm | all meek then uniting |
|
e.g. <lang algol68>UNION(INT,REAL) var := 1</lang> |
strong | all firm followed by widening, rowing or voiding | Right hand side of:
Also:
|
Widening occures 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:
<lang algol68>INT to LONG INT INT to REAL REAL to COMPL BITS to []BOOL BYTES to STRING</lang> A variable can also be coerced (rowed) to an array of length 1. For example: <lang algol68>INT to [1]INT REAL to [1]REAL</lang> etc |
For more details about Primaries and Secondaries refer to Operator precedence.
Code Specimen
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 1,021 total.
(previous page) (next page)H
I
- I before E except after C
- Iccanobif primes
- Identity matrix
- Idiomatically determine all the characters that can be used for symbols
- Idiomatically determine all the lowercase and uppercase letters
- Idoneal numbers
- Implicit type conversion
- Include a file
- Inconsummate numbers in base 10
- Increasing gaps between consecutive Niven numbers
- Increment a numerical string
- Infinity
- Inner classes
- Input loop
- Input/Output for lines of text
- Input/Output for pairs of numbers
- Integer comparison
- Integer overflow
- Integer sequence
- Intersecting number wheels
- Introspection
- Inventory sequence
- Inverted syntax
- ISBN13 check digit
- Isograms and heterograms
- Isqrt (integer square root) of X
- Iterated digits squaring
J
K
L
- L-system
- Lah numbers
- Langton's ant
- Largest difference between adjacent primes
- Largest five adjacent number
- Largest int from concatenated ints
- Largest number divisible by its digits
- Largest palindrome product
- Largest prime factor
- Largest product in a grid
- Largest proper divisor of n
- Last Friday of each month
- Last list item
- Law of cosines - triples
- Leap year
- Least common multiple
- Least m such that n! + m is prime
- Left factorials
- Length of an arc between two angles
- Leonardo numbers
- Letter frequency
- Levenshtein distance
- Linear congruential generator
- List comprehensions
- Literals/Floating point
- Literals/Integer
- Literals/String
- Logical operations
- Long multiplication
- Long primes
- Long year
- Longest common prefix
- Longest common subsequence
- Longest common substring
- Longest common suffix
- Longest palindromic substrings
- Longest string challenge
- Look-and-say sequence
- Loop over multiple arrays simultaneously
- Loops/Break
- Loops/Continue
- Loops/Do-while
- Loops/Downward for
- Loops/For
- Loops/For with a specified step
- Loops/Foreach
- Loops/Increment loop index within loop body
- Loops/Infinite
- Loops/N plus one half
- Loops/Nested
- Loops/While
- Loops/With multiple ranges
- Loops/Wrong ranges
- Lucas-Lehmer test
- Ludic numbers
- Luhn test of credit card numbers
- Lychrel numbers
M
- Mad Libs
- Magic 8-ball
- Magic constant
- Magic numbers
- Magic squares of doubly even order
- Magic squares of odd order
- Magic squares of singly even order
- Magnanimous numbers
- Man or boy test
- Mandelbrot set
- Map range
- Matrix multiplication
- Matrix transposition
- Matrix with two diagonals
- Matrix-exponentiation operator
- Maximum difference between adjacent elements of list
- Maximum triangle path sum
- McNuggets problem
- MD5
- Meissel–Mertens constant
- Memory allocation
- Memory layout of a data structure
- Menu
- Mersenne primes
- Mertens function
- Metaprogramming
- Metered concurrency
- Mian-Chowla sequence
- Middle three digits
- Miller–Rabin primality test
- Minimum multiple of m where digital sum equals m
- Minimum number of cells after, before, above and below NxN squares
- Minimum numbers of three lists
- Minimum positive multiple in base 10 using only 0 and 1
- Minimum primes
- Modified random distribution
- Modular arithmetic
- Modular exponentiation
- Modular inverse
- Monads/Maybe monad
- Monads/Writer monad
- Monte Carlo methods
- Monty Hall problem
- Mosaic matrix
- Motzkin numbers
- Move-to-front algorithm
- Multi-dimensional array
- Multifactorial
- Multiple distinct objects
- Multiple regression
- Multiplication tables
- Multiplicative order
- Multiplicatively perfect numbers
- Multisplit
- Munchausen numbers
- Mutual recursion
- Möbius function
N
- N'th
- N-body problem
- N-grams
- N-queens problem
- Named parameters
- Naming conventions
- Narcissist
- Narcissistic decimal number
- Native shebang
- Negative base numbers
- Neighbour primes
- Nested function
- Next highest int from digits
- Nice primes
- Nim game
- Non-continuous subsequences
- Non-decimal radices/Convert
- Non-decimal radices/Input
- Non-decimal radices/Output
- Non-transitive dice
- Nth root
- Null object
- Number names
- Number reversal game
- Numbers divisible by their individual digits, but not by the product of their digits.
- Numbers in base 10 that are palindromic in bases 2, 4, and 16
- Numbers in base-16 representation that cannot be written with decimal digits
- Numbers k such that the last letter of k is the same as the first letter of k+1
- Numbers which are not the sum of distinct squares
- Numbers which are the cube roots of the product of their proper divisors
- Numbers whose binary and ternary digit sums are prime
- Numbers whose count of divisors is prime
- Parameter passing/By reference
- Parameter passing/By value
- Typing/Safe
- Typing/Soft, weak, meek, firm and strong - depending on context.
- Typing/Compatibility/Structural
- Typing/Expression/Explicit
- Typing/Checking/Dynamic
- Typing/Checking/Static
- Programming Languages
- Programming paradigm/Concurrent
- Programming paradigm/Imperative