listing/0) and with one argument (
listing/1). With no arguments, it causes the contents of the Prolog database to be printed out. With one argument - the name of a procedure - it prints out just the rules and/or facts relating to that procedure. Examples, assuming you have started Prolog with a program file that contains the facts and rules
happy(ann). happy(tom). happy(X) :- rich(X). rich(fred).
?- listing. happy(ann). happy(tom). happy(A) :- rich(A). rich(fred). true. ?- listing(happy). happy(ann). happy(tom). happy(A) :- rich(A). true.
In the case of
listing/0, Prolog may also print out
some internal house-keeping information.