4.15.2 Raising Exceptions

You can raise exceptions from your own code using one of the two equivalent built-in predicates:


The argument to this predicate is the exception term; it is an arbitrary non-variable term of which the principal functor indicates the exception class. You can use the same exception classes as the system (see ref-ere-err), or you can use your own exception classes.

See lib-types for an alternative interface to raising error exceptions, which tries to include line number information for source-linked debugging.

Error messages like the one shown above are printed using the built-in predicate print_message/2. One of the arguments to print_message/2 is the exception term. print_message/2 can be extended, as described in ref-msg, so that you can have appropriate error messages printed corresponding to your own exception classes.

Please note: If the exception term contains attributed variables (see lib-atts) or suspended goals (see ref-sem-sec), those attributes do not become part of the exception. To retain the attributes, you can use copy_term/3 (see ref-lte-cpt).

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