The Free On-line Dictionary of Computing (30 December 2018):

ALGOL 68

    An extensive revision of ALGOL 60 by Adriaan van
   Wijngaarden et al.  ALGOL 68 was discussed from 1963 by
   Working Group 2.1 of IFIP.  Its definition was accepted in
   December 1968.

   ALGOL 68 was the first, and still one of very few, programming
   languages for which a complete formal specification was
   created before its implementation.  However, this
   specification was hard to understand due to its formality, the
   fact that it used an unfamiliar metasyntax notation (not
   BNF) and its unconventional terminology.

   One of the singular features of ALGOL 68 was its orthogonal
   design, making for freedom from arbitrary rules (such as
   restrictions in other languages that arrays could only be used
   as parameters but not as results).  It also allowed user
   defined data types, then an unheard-of feature.

   It featured structural equivalence; automatic type
   conversion ("coercion") including dereferencing; flexible
   arrays; generalised loops (for-from-by-to-while-do-od),
   if-then-else-elif-fi, an integer case statement with an 'out'
   clause (case-in-out-esac); skip and goto statements;
   blocks; procedures; user-defined operators; procedure
   parameters; concurrent execution (par-begin-end);
   semaphores; generators "heap" and "loc" for dynamic
   allocation.  It had no abstract data types or separate
   compilation.

   (http://www.bookrags.com/research/algol-68-wcs/).

   (2007-04-24)