Prolog is the kind of language that is sold on being declarative, but ultimately you have to study how the unification algorithm works. And probably also sprink

Prolog is the kind of language that is sold on being declarative, but ultimately you have to study how the unification algorithm works. And probably also sprinkle cuts around your code in order to not let the runtime do too much work, or maybe so that it will work correctly. Granted I've only used it in one university course (and only half of that course).