Snap is a way to distribute applications as self-contained images. This allows a snap to work on any Linux distribution that has snapd installed and runs a compatible architecture (currently amd64).

Snaps for SWI-Prolog are available since version 8.1.28. Snaps are distributed in the following channels:

• stable is the default and installs the latest stable release, currently 8.2.x.
• candidate and beta will be used for the next stable cycle (8.4.0) to prepare the final next stable
• edge will follow the roughly biweekly releases of the development cycle (8.3.x).

Thus, typically one would use

snap install swi-prolog		# install stable release
snap install --edge swi-prolog	# install devel release

The swi-prolog snap provides two commands, the first being a console application and the second the Qt window version.

swi-prolog.swipl
swi-prolog.swipl-win

You can get the usual command names swipl and swipl-win installed in `/snap/bin` using these commands

snap alias swi-prolog.swipl swipl
snap alias swi-prolog.swipl-win swipl-win

Snaps have advantages and disadvantages. It should be easy enough to find details about that. The snap is probably the most convenient way for the casual user who wants a fairly up-to-date version and doesn't like to go through the build process.

Confined snap

The current snap is a confined snap, which means it has only limited access to your computer. This keeps the snap small as it is layered on top of other snaps and brings some additional security, but also implies (for example) that you cannot run arbitrary programs from the snap and you cannot install add-ons that contain components written in e.g., C.

Font issue

There is a glitch in current snap infrastructure for handling the fontconfig library which is used by the xpce based IDE tools. You are a victim if running ?- emacs. results in the error below:

?- emacs.
[PCE fatal: @helvetica_roman_12/font: Xopen failed on @display/display
        in:     <No exception goal>
]
        [13] M @helvetica_roman_12/font ->_xopen(@display/display)
        [12] M @helvetica_roman_12/font ->_xopen(@display/display)
...

This can be resolved by cleaning the fontconfig global cache. Doing so has no consequences except for the first application to use fontconfig starting slow.

sudo rm /var/cache/fontconfig/*

Status of the snap images

Snap images for SWI-Prolog are new. We do not know whether or not there are issues with them and we may change the packaging and confinement.