An example

We illustrate the use of dyalog on a small recursive example that will loop with standard Prolog systems.

     % cat pgm.pl
     q(f(f(a))).
     q(X) :- q(f(X)).
     ?-q(X).    % the query must be inside the file
     
     % dyacc pgm.pl -o pgm
     % ./pgm
     Answer:
         X = f(f(a))
     Answer:
         X = f(a)
     Answer:
         X = a