2.1.2 Adding rules from the console

Although we strongly advice to put your program in a file, optionally edit it and use make/0 to reload it (see section 2.1.4), it is possible to manage facts and rules from the terminal. The most convenient way to add a few clauses is by consulting the pseudo file user. The input is ended using the system end-of-file character.

?- [user].
|: hello :- format('Hello world~n').
|: ^D
true.

?- hello.
Hello world
true.

The predicates assertz/1 and retract/1 are alternatives to add and remove rules and facts.