Algol 68

1
Algol 68

• Third language in the Algol Language Family
• An extension to Algol 60's capabilities
• Code blocks
• Variable Scopes
• Algol 68 was known for its orthogonality
• The goal was to develop a language with few
  language restrictions.
• Intended to make the language easier to learn

2
Algol 68

• Algol 68 Basic Features
• Common Language Services IF ... THEN ...
  ELSE,ELSE-IF, WHILE, DO ... WHILE, FOR ... NEXT
• Procedural Abstraction Can define new procedures
  and functions for generalizing tasks.
• Dynamic Arrays Arrays, of any type, can shrink
  and grow dynamically. This is also called flex
  arrays. Arrays can be of any dimensions.
• Array Slicing Using special syntax, new arrays
  can be created from old arrays.

3
Algol 68

• Algol 68 Basic Features
• Operator Definition And Overloading Users can
  create new operators, overload existing operators
  using user types and change the priority of
  operators.
• Highly Orthogonal. Examples
• 3 (a c 4) 2
• X IF a lt 2 THEN 3.2 ELSE 5.2 FI
• IF a lt 2 x THEN y FI 3.5
• Strong Type Checking
• Users can use system-provided modes or can
  define new modes through new structures or
  unions.

4
Algol 68

• Algol 68 Basic Features
• Support for call-by-value as well as
  call-by-reference.
• All procedures defined are values, with their
  names as values Can use Algol 68 for some
  functional programming.
• Algol 68 Library Support
• I/O facilities provided through
  architecture-independent transput (unlike what
  was provided with Algol 68.)
• Current implementations provide support for
  scientific code libraries.

5
Algol 68

• Examples

PROC factorial (INT x)INT BEGIN (x 1 OR
x 0xx factorial(x-1)) END PROC map and
print (INT x, PROC (INT)INT
proc)VOID BEGIN FOR i FROM LWB x TO UPB x
DO print(proc(xi) OD END
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Algol 68

• More Examples of Orthogonality

REF INT size LOC INT read(size) REFINT a
LOC1sizeINT could also be done as REFINT r
LOC1(REF INT iLOC INT read(i)i)INT