So am being told a specific predicate has to work in +,+ mode. What does that mean in Prolog?
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So am being told a specific predicate has to work in +,+ mode. What does that mean in Prolog?
When one wants to give information on a predicate in prolog, those conventions are often used :
arity : predicate/3 means predicate takes 3 arguments.
parameters : predicate(+Element, +List, -Result) means that Element and List should not be free variables and that Result should be a free variable for the predicate to work properly. ? is used when it can be both, @ is mentionned on the above answer but is not really used as much (at least in swi-pl doc) and means that the input will not be bound during the call.
so telling that somepredicate works in +, + mode is a shortcut for telling that :