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|Hooks for integrating libraries|
Some libraries realise an entirely new programming paradigm on top of Prolog. An example is XPCE which adds an object system to Prolog as well as an extensive set of graphical primitives. SWI-Prolog provides several hooks to improve the integration of such libraries. See also section A.20 for editing hooks and section 4.11 for hooking into the message system.
userto list the currently called predicate. This hook may be defined to list only relevant clauses of the indicated Goal and/or show the actual source code in an editor. See also portray/1 and multifile/1.
?- help(picture).is caught by the XPCE help hook to give help on the class picture. Defined actions are: