Editing ALGOL 68 (section)

==Examples of use==

===Code sample===
This sample program implements the [[Sieve of Eratosthenes]] to find all the [[prime number]]s that are less than 100. '''NIL''' is the ALGOL 68 analogue of the ''null pointer'' in other languages. The notation ''x'' '''OF''' ''y'' accesses a member ''x'' of a '''STRUCT''' ''y''.

 '''BEGIN''' # Algol-68 prime number sieve, functional style #
  &nbsp;
   '''PROC''' error = ('''STRING''' s) '''VOID''':
      (print(( newline, " error: ", s, newline)); '''GOTO''' stop);
   '''PROC''' one to = ('''INT''' n) '''LIST''':
      ('''PROC''' f = ('''INT''' m,n) '''LIST''': (m>n | '''NIL''' | cons(m, f(m+1,n))); f(1,n));
  &nbsp;
   '''MODE''' '''LIST''' = '''REF''' '''NODE''';
   '''MODE''' '''NODE''' = '''STRUCT''' ('''INT''' h, '''LIST''' t);
   '''PROC''' cons = ('''INT''' n, '''LIST''' l) '''LIST''': '''HEAP''' '''NODE''' := (n,l);
   '''PROC''' hd   = ('''LIST''' l) '''INT''': ( l '''IS''' '''NIL''' | error("hd '''NIL'''"); '''SKIP''' | h '''OF''' l );
   '''PROC''' tl   = ('''LIST''' l) '''LIST''': ( l '''IS''' '''NIL''' | error("tl '''NIL'''"); '''SKIP''' | t '''OF''' l );
   '''PROC''' show = ('''LIST''' l) '''VOID''': ( l '''ISNT''' '''NIL''' | print((" ",whole(hd(l),0))); show(tl(l)));
  &nbsp;
   '''PROC''' filter = ('''PROC''' ('''INT''') '''BOOL''' p, '''LIST''' l) '''LIST''':
      '''IF''' l '''IS''' '''NIL''' '''THEN''' '''NIL'''
      '''ELIF''' p(hd(l)) '''THEN''' cons(hd(l), filter(p,tl(l)))
      '''ELSE''' filter(p, tl(l))
      '''FI''';
  &nbsp;
   '''PROC''' sieve = ('''LIST''' l) '''LIST''':
      '''IF''' l '''IS''' '''NIL''' '''THEN''' '''NIL'''
      '''ELSE'''
         '''PROC''' not multiple = ('''INT''' n) '''BOOL''': n '''MOD''' hd(l) ~= 0;
         cons(hd(l), sieve( filter( not multiple, tl(l) )))
      '''FI''';
  &nbsp;
   '''PROC''' primes = ('''INT''' n) '''LIST''': sieve( tl( one to(n) ));
  &nbsp;
   show( primes(100) )
 '''END'''

===Operating systems written in ALGOL 68===
* [[Cambridge CAP computer]] – All procedures constituting the operating system were written in [[ALGOL 68C]], although several other closely associated protected procedures, such as a paginator, are written in [[BCPL]].<ref>{{Cite journal |last1=Needham |first1=R. M. |last2=Wilkes |first2=M. V. |date=January 1979 |url=http://research.microsoft.com/pubs/72418/cap.pdf |title=The Cambridge CAP Computer and its Operating System| journal=Microsoft Research}}</ref>
* Eldon 3 – Developed at [[Leeds University]] for the [[ICT 1900 series|ICL 1900]] was written in [[ALGOL 68-R]].<ref name="eldon">{{cite web |title=KDF9 Time Sharing: Eldon 2 is not EGDON! |url=http://www.cs.man.ac.uk/CCS/res/res49.htm#e|author=David Holdsworth |date=Winter 2009–2010 |work=Computer Resurrection – Number 49 |publisher=[[Computer Conservation Society]] |access-date=2010-10-03}}</ref>
* [[Flex machine]] – The hardware was custom and microprogrammable, with an operating system, (modular) compiler, editor, garbage collector and filing system all written in [[ALGOL 68RS]]. The command shell Curt<ref>{{cite web|url=http://www.vitanuova.com/dist/doc/rsre-3522-curt.pdf|access-date=7 April 2023|website=vitanuova.com|title=RSRE Memorandum |date=September 1982|author1=I F Currie|author2=J M Foster}}</ref> was designed to access typed data similar to Algol-68 modes.
* [[ICL VME|VME]] – [[S3 (programming language)|S3]] was the implementation language of the [[operating system]] VME. S3 was based on ALGOL 68 but with data types and operators aligned to those offered by the [[ICL 2900 Series]].
Note: The Soviet Era computers [[Elbrus (computer)|Эльбрус-1 (Elbrus-1)]] and Эльбрус-2 were created using high-level language Эль-76 (AL-76), rather than the traditional assembly. Эль-76 resembles Algol-68, The main difference is the dynamic binding types in Эль-76 supported at the hardware level. Эль-76 is used for application, job control, system programming.<ref>[http://www.ixbt.com/cpu/e2k-spec.html Эльбрус Бабаяна и Pentium Пентковского]. Ixbt.com. Retrieved 21 July 2013.</ref>

===Applications===
Both [[ALGOL 68C]] and [[ALGOL 68-R]] are written in ALGOL 68, effectively making ALGOL 68 an application of itself. Other applications include:

* [[ELLA (programming language)|ELLA]] – a hardware description language and support toolset. Developed by the [[Royal Signals and Radar Establishment]] during the 1980s and 1990s.
* [[RAF Strike Command]] System – "... 400K of error-free [[ALGOL 68-RT]] code was produced with three man-years of work. ..."<ref>{{cite journal |last1=Oliver |first1=J. R. |last2=Newton |first2=R. S. |date=1979 |title=Practical experience with ALGOL 68-RT |journal=The Computer Journal |volume=22 |issue=2 |pages=114–118 |doi=10.1093/comjnl/22.2.114|doi-access=free }}</ref>

===Libraries and APIs===
* [[NAG Numerical Libraries]] – a [[software library]] of [[numerical analysis]] routines. Supplied in ALGOL 68 during the 1980s.
* TORRIX – a programming system for operations on vectors and matrices over arbitrary fields and of variable size by S. G. van der Meulen and M. Veldhorst.<ref name="torrix">[http://www.softwarepreservation.org/projects/ALGOL/applications#ALGOL_68_Libraries Applications, libraries, and test suites — Software Preservation Group]. Softwarepreservation.org. Retrieved 21 July 2013.</ref>