It describes calculations or operations, so functional code still seems to perform or describe some actions. Constraint logic programs seem more of the grey ar

It describes calculations or operations, so functional code still seems to perform or describe some actions. Constraint logic programs seem more of the grey area I think you're talking about. Is a set of constraints "code" (c.f. https://en.wikibooks.org/wiki/Prolog/Solving_a_Logic_Puzzle#Complete_solution https://en.wikibooks.org/wiki/Prolog/Solving_a_Logic_Puzzle#... )?