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).
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.
last). Using
first, new packages are added at the start.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.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.
last, alternative is first.