A.11 library(debug): Print debug messages and test assertions
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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.
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