Here's a list of commands that will be useful in loading and running PROLOG programs. The best way to use a Prolog environment is to save your database in a regular ASCII text file, named with the suffix pro or pl (but note that Perl files also use the pl suffix). Then you repeatedly load the file into the interpreter and run queries.

A complete listing of the GPROLOG (Gnu Prolog) commands will be provided as a handout.

^D              /* Control-D exits Prolog at the query prompt. */
^C              /* Control-C interrupts any query and puts Prolog in interrupt mode:
                | ?-
                Prolog interruption (h for help) ? h
                   a  abort        b  break
                   c  continue     e  exit
                   d  debug        t  trace
                   h/? help

                Prolog interruption (h for help) ? e    /* We exit PROLOG */

                /* A PROLOG program can dynamically modify its database               */
                /*  Or you can add a predicate from the query prompt.                 */
asserta(P).     /* Adds P to the front of all matching P's                            */
assertz(P).     /* Adds P to the end of all matching P's                              */
retract(P).     /* Removes P from the database: -- e.g., (retract(male(joe)).

                /* A PROLOG database can be loaded from a preexisting ascii file:     */

consult('filename').  /* PROLOG reads the database into the interpreter reporting any     */ 
                      /*  syntax errors. If you have errors, fix then and consult again.  */
                      /*  NOTE. Some versions of PROLOG will create duplicate facts       */
                      /*   and rules if you consult() the same file more than once.       */
                      /*   Some versions, but not GPROLOG, have a reconsult() predicate   */

reconsult('filename'). /* Reconsult the named file. Don't duplicate existing predicates. */

['file1','file2'].     /* List notation can be used to load more than one file at once. */

listing.              /* This predicate provides a listing of the database. */
listing(P).           /* Provides a listing of just the predicate P.        */

trace                 /* Turns on Prolog's trace utility. This dumps everything. */
notrace.              /* Turns off the trace utility. */

spy(P).               /* This just traces the predicate P */
nospy(P).             /* Removes the spy point on P */