prolog_debug:assertion/1

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Predicate assertion/1

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Documentation
- Reference manual
  - The SWI-Prolog library
    - library(debug): Print debug messages and test assertions
- Packages

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

Source

[det]assertion(:Goal)

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.