4.15.3 Handling Exceptions

• ref-ere-hex-pgo: Protecting a Particular Goal
• ref-ere-hex-hup: Handling Unknown Predicates

It is possible to protect a part of a program against abrupt termination in the event of an exception. There are several ways to do this:

• Trap exceptions to a particular goal by calling catch/3 as described in ref-ere-hex-pgo.
• Handle undefined predicates or subsets of them through the hook predicate user:unknown_predicate_handler/3; see ref-ere-hex-hup.
• Trap exceptions matching Exception to the debugger by defining the following hook predicate:

  user:error_exception(+Exception)   hook,development

  See mpg-ref-error_exception.

• Control syntax errors with the syntax_errors Prolog flag or with the same option to read_term/[2,3]; see ref-ere-err-syn.
• Control existence and permission errors in the context of opening files with the fileerrors Prolog flag or with the same option to absolute_file_name/3; see ref-ere-err-exi and ref-ere-err-per.