Modules normally are created by loading a module file. A module file is a file holding a module/2 directive as its first term. The module/2 directive declares the name and the public (i.e., externally visible) predicates of the module. The rest of the file is loaded into the module. Below is an example of a module file, defining reverse/2.
:- module(reverse, [reverse/2]).
reverse(List1, List2) :-
rev(List1, [], List2).
rev([], List, List).
rev([Head|List1], List2, List3) :-
rev(List1, [Head|List2], List3).