Category:ALGOL 68: Difference between revisions
m →Grammar: http://www.softwarepreservation.org/projects/ALGOL/book/Lindsey_van_der_Meulen-IItA68-Revised-SyntaxOnly.pdf/view |
→Coercion (casting): more details |
||
Line 143: | Line 143: | ||
ALGOL 68 has a hierarchy of contexts which determine which kind of |
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: |
coercions are available at a particular point in the program. These contexts are: |
||
{|class="wikitable" |
|||
⚫ | |||
! Context name !! Coercions applied in this context !! Context location !! Coercion examples |
|||
* weak - dereferencing or deproceduring, yielding a name |
|||
|- |
|||
* meek - dereferencing or deproceduring |
|||
⚫ | |||
* firm - meek, followed by uniting |
|||
|| The LHS of assignments, as in: <lang algol68>:=</lang> |
|||
⚫ | |||
|| |
|||
* deproceduring of: <lang algol68>PROC REAL random: e.g. random</lang> |
|||
Depending on the context a MODE (type) will be coerced (widened) to another type if there is no loss |
|||
|- |
|||
⚫ | |||
|weak || all ''soft'' above then weak dereferencing |
|||
coerced to a LONG REAL. But not vice-versa. Examples: |
|||
|| |
|||
⚫ | |||
* Primaries of slices |
|||
⚫ | |||
* Secondaries of selections, as in: <lang algol68>OF</lang> |
|||
⚫ | |||
|| |
|||
⚫ | |||
<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 |
|||
⚫ | |||
<lang algol68>INT to LONG INT |
|||
⚫ | |||
⚫ | |||
⚫ | |||
⚫ | |||
A variable can also be coerced (rowed) to an array of length 1. For example: |
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 |
|||
|} |
|||
Pointers are followed (dereferenced), For example: |
|||
For more details about Primaries and Secondaries refer to [[Operator_precedence#ALGOL_68|Operator precedence]]. |
|||
⚫ | |||
== Code Specimen == |
== Code Specimen == |
||
{{language programming paradigm|Concurrent}} |
{{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 1,023 total.
(previous page) (next page)A
- A+B
- Abbreviations, easy
- Abbreviations, simple
- ABC problem
- ABC words
- Abelian sandpile model
- Abelian sandpile model/Identity
- Abundant odd numbers
- Abundant, deficient and perfect number classifications
- Accumulator factory
- Achilles numbers
- Ackermann function
- Additive primes
- Address of a variable
- AKS test for primes
- Align columns
- Aliquot sequence classifications
- Almkvist-Giullera formula for pi
- Almost prime
- Alternade words
- Amb
- Amicable pairs
- Anadromes
- Anagrams
- Anagrams/Deranged anagrams
- Anaprimes
- Angle difference between two bearings
- Angles (geometric), normalization and conversion
- Anonymous recursion
- Anti-primes
- Append numbers at same position in strings
- Apply a callback to an array
- Apply a digital filter (direct form II transposed)
- Approximate equality
- Apéry's constant
- Arbitrary-precision integers (included)
- Archimedean spiral
- Arithmetic derivative
- Arithmetic evaluation
- Arithmetic numbers
- Arithmetic-geometric mean
- Arithmetic/Complex
- Arithmetic/Integer
- Arithmetic/Rational
- Array concatenation
- Array length
- Arrays
- Ascending primes
- ASCII control characters
- Assertions
- Associative array/Creation
- Associative array/Iteration
- Associative array/Merging
- Attractive numbers
- Averages/Arithmetic mean
- Averages/Mean angle
- Averages/Mean time of day
- Averages/Median
- Averages/Mode
- Averages/Pythagorean means
- Averages/Root mean square
- Averages/Simple moving average
B
- B-spline
- Babbage problem
- Bacon cipher
- Balanced brackets
- Balanced ternary
- Barnsley fern
- Base 16 numbers needing a to f
- Base64 encode data
- Bell numbers
- Benford's law
- Bernoulli numbers
- Bernstein basis polynomials
- Best shuffle
- Bin given limits
- Binary coded decimal
- Binary digits
- Binary search
- Binary strings
- Binomial transform
- Bioinformatics/base count
- Birthday problem
- Bitmap
- Bitmap/Bresenham's line algorithm
- Bitmap/Bézier curves/Cubic
- Bitmap/Midpoint circle algorithm
- Bitwise IO
- Bitwise operations
- Blum integer
- Boolean values
- Boustrophedon transform
- Box the compass
- Brilliant numbers
- Bulls and cows
- Bulls and cows/Player
C
- Caesar cipher
- Calculating the value of e
- Calendar
- Calendar - for "REAL" programmers
- Calkin-Wilf sequence
- Call a foreign-language function
- Call a function
- Call an object method
- Calmo numbers
- CalmoSoft primes
- Camel case and snake case
- Canonicalize CIDR
- Cantor set
- Carmichael 3 strong pseudoprimes
- Cartesian product of two or more lists
- Case-sensitivity of identifiers
- Casting out nines
- Catalan numbers
- Catalan numbers/Pascal's triangle
- Catamorphism
- Centre and radius of a circle passing through 3 points in a plane
- Centroid of a set of N-dimensional points
- Change e letters to i in words
- Changeable words
- Character codes
- Chebyshev coefficients
- Check if a polygon overlaps with a rectangle
- Check if two polygons overlap
- Check that file exists
- Chemical calculator
- Cheryl's birthday
- Chinese remainder theorem
- Chinese zodiac
- Cholesky decomposition
- Chowla numbers
- Circles of given radius through two points
- Circular primes
- Cistercian numerals
- Classes
- Closures/Value capture
- Code Golf: Code Golf
- Collect and sort square numbers in ascending order from three lists
- Collections
- Colorful numbers
- Combinations
- Combinations and permutations
- Comma quibbling
- Command-line arguments
- Commatizing numbers
- Comments
- Common list elements
- Compare a list of strings
- Compare length of two strings
- Compiler/code generator
- Compiler/lexical analyzer
- Compiler/Simple file inclusion pre processor
- Composite numbers k with no single digit factors whose factors are all substrings of k
- Compound data type
- Concatenate two primes is also prime
- Concurrent computing
- Conditional structures
- Conjugate a Latin verb
- Conjugate transpose
- Consecutive primes with ascending or descending differences
- Constrained random points on a circle
- Continued fraction
- Continued fraction/Arithmetic/Construct from rational number
- Convert CSV records to TSV
- Convert seconds to compound duration
- Conway's Game of Life
- Coprime triplets
- Coprimes
- Copy a string
- Copy stdin to stdout
- CORDIC
- Count how many vowels and consonants occur in a string
- Count in factors
- Count in octal
- Count occurrences of a substring
- Count the coins
- Count the coins/0-1
- Cousin primes
- Cramer's rule
- CRC-32
- Create a file
- Create a two-dimensional array at runtime
- Create an executable for a program in an interpreted language
- Create an HTML table
- CSV data manipulation
- CSV to HTML translation
- Cuban primes
- Cubic special primes
- Cullen and Woodall numbers
- Cumulative standard deviation
- Currency
- Currying
- Curve that touches three points
- Curzon numbers
- 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