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)D
- Damm algorithm
- Date format
- Day of the week
- Day of the week of Christmas and New Year
- Days between dates
- De Polignac numbers
- Death Star
- Deceptive numbers
- Decorate-sort-undecorate idiom
- Define a primitive data type
- Delegates
- Delete a file
- Department numbers
- Descending primes
- Detect division by zero
- Determine if a string has all the same characters
- Determine if a string has all unique characters
- Determine if a string is collapsible
- Determine if a string is numeric
- Determine if a string is squeezable
- Determine if two triangles overlap
- Determine sentence type
- Digit fifth powers
- Digital root
- Digital root/Multiplicative digital root
- Dijkstra's algorithm
- Dinesman's multiple-dwelling problem
- Disarium numbers
- Discordian date
- Display a linear combination
- Distinct power numbers
- Diversity prediction theorem
- Doomsday rule
- Dot product
- Double Twin Primes
- Doubly-linked list/Definition
- Doubly-linked list/Element definition
- Doubly-linked list/Element insertion
- Doubly-linked list/Traversal
- Dragon curve
- Draw a cuboid
- Duffinian numbers
- Dutch national flag problem
- Dynamic variable names
E
- Earliest difference between prime gaps
- Eban numbers
- Egyptian division
- Element-wise operations
- Elementary cellular automaton
- Emirp primes
- Empty directory
- Empty program
- Empty string
- Enforced immutability
- Entropy
- Entropy/Narcissist
- Enumerations
- Environment variables
- Equal prime and composite sums
- Equilibrium index
- Erdős-Nicolas numbers
- Erdős-primes
- Esthetic numbers
- Ethiopian multiplication
- Euclid-Mullin sequence
- Euclidean rhythm
- Euler method
- Euler's identity
- Euler's sum of powers conjecture
- Evaluate binomial coefficients
- Even numbers which cannot be expressed as the sum of two twin primes
- Even or odd
- Evolutionary algorithm
- Exactly three adjacent 3 in lists
- Exceptions
- Exceptions/Catch an exception thrown in a nested call
- Execute a system command
- Execute Brain****
- Execute Computer/Zero
- Execute HQ9+
- Execute SNUSP
- Exponentiation operator
- Exponentiation order
- Exponentiation with infix operators in (or operating on) the base
- Extend your language
- Extra primes
- Extract file extension
- Extreme primes
F
- Factorial
- Factorial primes
- Factorions
- Factorize string into Lyndon words
- Factors of a Mersenne number
- Factors of an integer
- Fairshare between two and more
- Farey sequence
- Fast Fourier transform
- FASTA format
- Faulhaber's triangle
- Feigenbaum constant calculation
- Fermat numbers
- Fermat pseudoprimes
- Fibonacci n-step number sequences
- Fibonacci sequence
- Fibonacci word
- File extension is in extensions list
- File input/output
- File modification time
- File size
- Filter
- Find adjacent primes which differ by a square integer
- Find common directory path
- Find first and last set bit of a long integer
- Find first missing positive
- Find if a point is within a triangle
- Find limit of recursion
- Find minimum number of coins that make a given value
- Find prime n such that reversed n is also prime
- Find prime numbers of the form n*n*n+2
- Find square difference
- Find squares n where n+1 is prime
- Find the intersection of two lines
- Find the last Sunday of each month
- Find the missing permutation
- Find words which contain the most consonants
- Find words which contains all the vowels
- Find words which contains more than 3 e vowels
- Find words whose first and last three letters are equal
- Find words with alternating vowels and consonants
- Finite state machine
- First 9 prime Fibonacci number
- First perfect square in base n with n unique digits
- First power of 2 that has leading decimal digits of 12
- First-class functions
- First-class functions/Use numbers analogously
- Five weekends
- Fivenum
- FizzBuzz
- Flatten a list
- Flow-control structures
- Floyd's triangle
- Floyd-Warshall algorithm
- Forbidden numbers
- Forest fire
- Fork
- Formatted numeric output
- Fortunate numbers
- Forward difference
- Four sides of square
- Fractran
- Frobenius numbers
- Function composition
- Function definition
- Function prototype
- Fusc sequence
G
- Gamma function
- Gapful numbers
- Gauss-Jordan matrix inversion
- Gaussian elimination
- Gaussian primes
- General FizzBuzz
- Generalised floating point addition
- Generalised floating point multiplication
- Generate lower case ASCII alphabet
- Generate random numbers without repeating a value
- Generator/Exponential
- Generic swap
- Giuga numbers
- Goldbach's comet
- Golden ratio/Convergence
- Gradient descent
- Gray code
- Greatest common divisor
- Greatest element of a list
- Greatest subsequential sum
- Greedy algorithm for Egyptian fractions
- GSTrans string conversion
- Guess the number
- Guess the number/With feedback
- Guess the number/With feedback (player)
H
- Hailstone sequence
- Halt and catch fire
- Hamming numbers
- Happy numbers
- Harmonic series
- Harshad or Niven series
- Hashtron inference
- Haversine formula
- Hello world/Graphical
- Hello world/Line printer
- Hello world/Newbie
- Hello world/Newline omission
- Hello world/Standard error
- Hello world/Text
- Here document
- Heronian triangles
- Hex words
- Hickerson series of almost integers
- Higher-order functions
- Hilbert curve
- 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