6.11 Reserved Modules and using the‘user’module

As mentioned above, SWI-Prolog contains two special modules. The first one is the module system. This module contains all built-in predicates. Module system has no import module, i.e., is a root of the module graph. The second special module is the module user. This module forms the initial working space of the user. Initially it is empty.^{187Unfortunately some hooks are traditionally defined in the user module}. The import module of module user is system, making all built-in predicates available.

All normal application modules import from the module user. This implies they can use all predicates imported into user without explicitly importing them. If an application loads all modules from the user module using use_module/1, one achieves a scoping system similar to the C-language, where every module can access all exported predicates without any special precautions.

All library modules (see module_property/2) import directly from system. Library modules are modules loaded from the SWI-Prolog installation. As they import from system, the functionality of a library is not affected by operator or predicate definitions in the user module.