<div dir="ltr">Thanks for your quick response Zoltan. I'm not skilled enough in Prolog or Mercury yet to be sure I'm asking the question correctly, but I essentially want to know if the rule mortal(X):-man(X) and the predicate man(X) could be compiled into C# and if new instances such as man(john) and man(bob) could later be created during runtime, e.g. when a user clicks on the "create man" button in the GUI? Is this the purpose of mutables (from section 4 in the transition guide)? </div> <div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Jan 5, 2022 at 8:52 PM Zoltan Somogyi <<a href="mailto:zoltan.somogyi@runbox.com">zoltan.somogyi@runbox.com</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> On Wed, 5 Jan 2022 18:42:17 +0200, David Epstein <<a href="mailto:davideps@umich.edu" target="_blank">davideps@umich.edu</a>> wrote: > For example, given: > > mortal(X) :- man(X). > > How would I dynamically (from c#) declare "man(Socrates)." and then query > if "human(Socrates)"? While a Prolog program allows the set of clauses in a predicate to be altered during runtime with assert and retract, Mercury does not. Please read section 4 of the Prolog to Mercury transition guide for the reason why it doesn't, and the many other solutions Mercury programmers can choose from. Note that this has nothing to do with C#, or with pragma foreign_export. You should also note that a fact of the form "man(Socrates)" would in fact assert that *everyone* is a man, because - "Socrates" starts with an upper case letter, which means it is a variable, - any value in the declared argument type of the "man/1" predicate, which presumably is a type representing people, is an instance of this variable. Zoltan. </blockquote></div>