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user. Clauses for it may be defined in any module, including the user module. Name is the name of the resource (an atom). A resource name may contain any character, except for $ and :, which are reserved for internal usage by the resource library. Class describes the kind of object stored in the resource. In the current implementation, it is just an atom. FileSpec is a file specification that may exploit file_search_path/2 (see absolute_file_name/2).
Normally, resources are defined as unit clauses (facts), but the definition of this predicate also allows for rules. For proper generation of the saved state, it must be possible to enumerate the available resources by calling this predicate with all its arguments unbound.
Dynamic rules are useful to turn all files in a certain directory
into resources, without specifying a resource for each file. For
example, assume the file_search_path/2
refers to the resource directory containing icon files. The following
definition makes all these images available as resources:
resource(Name, image, icons(XpmName)) :- atom(Name), !, file_name_extension(Name, xpm, XpmName). resource(Name, image, XpmFile) :- var(Name), absolute_file_name(icons(.), [type(directory)], Dir) concat(Dir, '/*.xpm', Pattern), expand_file_name(Pattern, XpmFiles), member(XpmFile, XpmFiles).