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Predicate call_with_inference_limit/3
Availability:built-in
Sourcecall_with_inference_limit(:Goal, +Limit, -Result)
Equivalent to call(Goal), but limits the number of inferences for each solution of Goal.78This predicate was realised after discussion with Ulrich Neumerkel and Markus Triska.. Execution may terminate as follows:

  • If Goal does not terminate before the inference limit is exceeded, Goal is aborted by injecting the exception inference_limit_exceeded into its execution. After termination of Goal, Result is unified with the atom inference_limit_exceeded. Otherwise,
  • If Goal fails, call_with_inference_limit/3 fails.
  • If Goal succeeds without a choice point, Result is unified with !.
  • If Goal succeeds with a choice point, Result is unified with true.
  • If Goal throws an exception, call_with_inference_limit/3 re-throws the exception.

An inference is defined as a call or redo on a predicate. Please note that some primitive built-in predicates are compiled to virtual machine instructions for which inferences are not counted. The execution of predicates defined in other languages (e.g., C, C++) count as a single inference. This includes potentially expensive built-in predicates such as sort/2.

Calls to this predicate may be nested. An inner call that sets the limit below the current is honoured. An inner call that would terminate after the current limit does not change the effective limit. See also call_with_depth_limit/3 and call_with_time_limit/2.

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LogicalCaptain said (2020-11-02T16:47:14):0 upvotes 0 0 downvotes
Picture of user LogicalCaptain.

Try exceeding the limit:

?- call_with_inference_limit(
      bagof(X,between(1,inf,X),Bag),
      10,Result).

Result = inference_limit_exceeded ;
false.

Explicitly catch the injected exception:

?- call_with_inference_limit(
      catch(
         bagof(X,between(1,inf,X),Bag),
         ExTerm,
         format("Caught ~q\n",[ExTerm])),
      10,Result).

Caught inference_limit_exceeded
ExTerm = inference_limit_exceeded,
Result = !.

Gold!

Now I'm expecting a predicate call_with_energy_limit/3 with a limit given in Joule.

Stefan Kral said (2016-01-27T23:49:01):0 upvotes 0 0 downvotes
Picture of user Stefan Kral.

Concerning SWI-Prolog version 7.3.16: Is there a particular reason why call_with_inference_limit/3 leaves behind a superfluous choice point in the case Result == inference_limit_exceeded?

Looking at the source code of call_with_inference_limit/3 in boot/syspred.pl, I think that changing (Result0 == ! -> ! ; true) to (Result0 \== inference_limit_exceeded -> ! ; true) in line #665 could do the trick without causing much havoc... Have I been missing something?