prolog_debug:assertion/1

Availability::- use_module(library(debug)).(can be autoloaded)

Acts similar to C assert() macro. It has no effect if Goal succeeds. If Goal fails or throws an exception, the following steps are taken:

call prolog:assertion_failed/2. If prolog:assertion_failed/2 fails, then:
- If this is an interactive toplevel thread, print a message, the stack-trace, and finally trap the debugger.
- Otherwise, throw error(assertion_error(Reason, G),_) where Reason is one of fail or the exception raised.