2.15 Packs: community add-ons

SWI-Prolog has a mechanism for easy incorporation of community extensions. See the pack landing page for details and available packs. This section documents the built-in predicates to attach packs. Predicates for creating, registering and installing packs are provided by the library library(prolog_pack).

attach_packs

Attaches all packs in subdirectories of directories that are accessible through the file search path (see absolute_file_name/3) pack. The default for this search path is given below. See file_search_path/2 for the app_data search path.

user:file_search_path(pack, app_data(pack)).

The default path may be overruled with the environment variable SWIPL_PACK_PATH. This variable must contain a list of directories separated by the OS-specific path_sep.

The predicate attach_packs/0 is called on startup of SWI-Prolog.

attach_packs(+Directory)

attach_packs(+Directory, +Options)

Attach all packs that are subdirectories of Directory. Directory is translated into a physical directory using absolute_file_name/3. This implies it can be a term Alias(SubDir) and the search is relative to the current source file if Directory is not an absolute path and these predicates are used as a directive. Defined options are:

search(+Where)

Determines the order in which pack library directories are searched. Default is to add new packages at the end (last). Using first, new packages are added at the start.

duplicate(+Action)

Determines what happens if a pack with the same name is already attached. Default is warning, which prints a warning and ignores the new pack. Other options are keep, which is like warning but operates silently and replace, which detaches the old pack and attaches the new.

replace(+Boolean)

If true, unregister all packs before registering the new packs.

The predicate attach_packs/2 can be used to attach packages that are bundled with an application. With the option replace(true), attach_packs/2 ensures that the application only relies on bundled packs.