Packs are normally installed using the pack app. By default they are installed for the current user. Alternatively they can be installed system-wide using the --global option:

swipl pack install --global <from>

Using packs that are installed independently from the application your are working on has several drawbacks:

• It makes it harder to install your application elsewhere.
• If you have multiple applications, they may depend on different versions of a pack.

While using global and per user add-ons has been popular with many languages, modern environments often (also) provides more fine grained control over add-ons. For example, Python provides virtual environments and Node installs dependencies defined in package.json in a local directory node_modules.

SWI-Prolog allows installing packs in a designated directory using

swipl pack install --dir=<my-pack-dir> <spec>

Given a directory holding the packs for your application, your application may use the packs from there using attach_packs/2. For example, after installing all packs in a local directory packs, your application may use its dependencies from packs using the directive below. The option replace(true) makes it look only for packs in packs. See attach_packs/2 for its option to control the search and deal with possible conflicts.

:- attach_packs(packs, [replace(true)]).

Summarising, you can use local packs (say pack a and packs b and their dependencies by adding the above directive to your source code and initializing packs as

mkdir packs
swipl pack install --dir=packs a b

Using git

An even better controlled environment can be created if the packs on which you rely are available in git repositories and you use git for your application version management. In that case, we can add the required packs as git submodules. For example

git submodule add https://github.com/<owner>/<pack>.git packs/<pack>
...

Now we can use git to manage the exact version we use and download our dependencies using

git submodule update --init

If the pack contains foreign components for which no binaries are included it must be built. As of SWI-Prolog 9.3.18/9.2.10, this can be achieved using the command below.

swipl pack rebuild --dir=packs

Older versions can only achieve this from Prolog by calling attach_packs/2 as above and pack_rebuild/0,1. This can be done from the command line

swipl -g "attach_packs(packs,[replace(true)])" -g pack_rebuild -t halt