Handling Unknown Predicates

Users can write a handler for the specific exception occurring when an undefined predicate is called by defining clauses for the hook predicate user:unknown_predicate_handler/3. This can be thought of as a “global” exception handler for this particular exception, because unlike on_exception/3, its effect is not limited to a particular goal. Furthermore, the exception is handled at the point where the undefined predicate is called.

The handler can be written to apply to all unknown predicates, or to a class of them. The reference page contains an example of constraining the handler to certain predicates.

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