/usr/local/lib/swipl/library/settings.pl
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 load_settings(File) is det
 load_settings(File, +Options) is det
Load local settings from File. Succeeds if File does not exist, setting the default save-file to File. Options are:
undefined(+Action)
Define how to handle settings that are not defined. When error, an error is printed and the setting is ignored. when load, the setting is loaded anyway, waiting for a definition.

If possibly changed settings need to be persistent, the application must call save_settings/0 as part of its shutdown. In simple cases calling at_halt(save_settings) is sufficient.