11.3.243 unknown/2   [development]

Synopsis

unknown(-OldAction, +NewAction)

Unifies OldAction with the current action on unknown procedures, i.e. the current value of the unknown Prolog flag, sets the current action to NewAction, and prints a message about the change.

Arguments

OldAction

one of [error,fail,trace,warning]

NewAction

one of [error,fail,trace,warning], must be nonvar

Description

This is merely a front-end to the unknown Prolog flag, which see. Note that:

     | ?- unknown(Action, Action).

just returns Action without changing it.

Procedures that are known to be dynamic just fail when there are no clauses for them.

Exceptions

instantiation_error

type_error

domain_error

Invalid NewAction.

See Also

Undefined Predicates, ref-ere, ref-lps-flg.