/usr/local/lib/swipl/library/settings.pl
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 set_setting(:Name, +Value) is det
Change a setting. Performs existence and type-checking for the setting. If the effective value of the setting is changed it broadcasts the event below. 
settings(changed(Module:Name, Old, New))

Note that modified settings are not automatically persistent. The application should call save_settings/0 to persist the changes.

Errors
- existence_error(setting, Name)
- type_error(Type, Value)