/usr/local/lib/swipl/library/settings.pl
All Application Manual Name SummaryHelp

 setting(:Name, +Type, +Default, +Comment) is det
Define a setting. Name denotes the name of the setting, Type its type. Default is the value before it is modified. Default can refer to environment variables and can use arithmetic expressions as defined by eval_default/4.

If a second declaration for a setting is encountered, it is ignored if Type and Default are the same. Otherwise a permission_error is raised.

Arguments:
Name- Name of the setting (an atom)
Type- Type for setting. One of any or a type defined by must_be/2.
Default- Default value for the setting.
Comment- Atom containing a (short) descriptive note.