Editing ALGOL 68 (section)

===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'''