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

Guarded Horn Clauses

    (GHC) A parallel dialect of Prolog by K. Ueda in
   which each clause has a guard.  GHC is similar to
   Parlog.  When several clauses match a goal, their guards
   are evaluated in parallel and the first clause whose guard is
   found to be true is used and others are rejected.  It uses
   committed-choice nondeterminism.

   See also FGHC, KL1.

   (1995-05-09)