A.47 library(settings): Setting management
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Availability::- use_module(library(settings)).(can be autoloaded)
Source[det]set_setting(:Name, +Value)
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)