
define_error(+Message, -N)

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



Arguments
   Message             String.
   N                   Variable.

Type
   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
   define_error(+, -) is det

Exceptions
     4 --- Message is not instantiated.
     5 --- Message is instantiated, but not to a string.
     5 --- 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
