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# request_notification(++Name, ++Pred)

Requests that a predicate be called when an option changes

Name
  Name of the option
Pred
  Predicate to call

## Description

Specifies that Pred(Name, OldValue, NewValue) should be called whenever the value of the option Name is changed. OldValue is the old value of the option that has just been replaced and NewValue is the new value that has just been assigned. Pred should not modify OldValue or NewValue in any way, as this may interfere with other notification predicates. Note also that any choice points left by the call to Pred are pruned upon success.

### Modules

This predicate is sensitive to its module context (tool predicate, see @/2).

## See Also

register_option / 3, set_option / 2