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define_error(+Message, -N)

Error number N is newly defined to give the message Message.
Message
String.
N
Variable.

This built-in predicate is obsolete!

Description

This predicate is used to define new user error types. Message is a string which is going to be printed when this error occurs (the string returned by error_id/2). N is bound to the new error number. The default error handler for the new error is error_handler/2.

Note that the error numbers should not be hard-coded in subsequent calls to error/2 etc., as the error numbers are arranged at run time and may be changed between releases.

Modes and Determinism

Exceptions

(4) instantiation fault
Message is not instantiated.
(5) type error
Message is instantiated, but not to a string.
(5) type error
N is instantiated.

Examples

Success:
      define_error("my first error message",N).  (gives N=340).
      define_error("my second error message",N). (gives N=341).

      [eclipse]: [user].
       :- define_error("1st arg should be number",N),
          setval(usererror, N).
       do(N,Res) :-(number(N) ->
              Res is sqrt(N)
              ;
              getval(usererror, Err),
              error(Err, do(N,Res))).
       user compiled 232 bytes in 0.00 seconds
      yes.
      [eclipse]: do(4,2.0).
      yes.
      [eclipse]: do(four,2.0).
      1st arg should be number in do(four, 2.0)
Error:
      define_error(M,N).                    (Error 4).
      define_error(atom,N).                 (Error 5).
      define_error("incorrect module",340). (Error 5).

See Also

set_event_handler / 2, error_id / 2