4.3 Loading Prolog source files
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Availability:built-in
Sourcerequire(+Predicates)
Declare that this file/module requires the specified predicates to be defined “with their commonly accepted definition''. Predicates is either a list of predicate indicators or a comma-list of predicate indicators. First, all built-in predicates are removed from the set. The remaining predicates are searched using the library index used for autoloading and mapped to a set of autoload/2 directives. This implies that the targets will be loaded lazily if autoloading is not completely disabled and loaded using use_module/2 otherwise. See autoload.

The require/1 directive provides less control over the exact nature and location of the predicate. As autoload/2, it prevents a local definition of this predicate. As SWI-Prolog guarantees that the set of built-in predicates and predicates available for autoloading is unambiguous (i.e., has no duplicates) the specification is unambiguous. It provides four advantages over autoload/2: (1) the user does not have to remember the exact library, (2) the directive can be supported in other Prolog systems55SICStus provides it, providing compatibility despite differences in library and built-in predicate organization, (3) it is robust against changes to the SWI-Prolog libraries and (4) it is less typing.