In theory, Prolog is the king of languages. Simultaneously a logical formalism, and (with a resolution system) a language for computation, AND the ultimate meta-programming language as its homoiconic but only goals are evaluated (there is no eager/lazy evaluation fuss - a term is just a term), and goals can only succeed (and have any consequence) if there is already a matching clause.
In practice, there are some very performant and maintained implementations with small but helpful communities.
Also in practice. With all of this power, it's clear that anything could be done (well) in Prolog, but it's not always clear what that way might be. DCGs are an example of a beautiful, elegant, simple, powerful way of building parsers (or state machines) that was not immediately evident to the Prolog community for some time. The perpetual conundrum as a user will be "I could do it this way, but there are certainly better ways of doing this, and I have many avenues I could explore, and I don't know which might be fruitful in what timeline".
In practice, there are some very performant and maintained implementations with small but helpful communities.
Also in practice. With all of this power, it's clear that anything could be done (well) in Prolog, but it's not always clear what that way might be. DCGs are an example of a beautiful, elegant, simple, powerful way of building parsers (or state machines) that was not immediately evident to the Prolog community for some time. The perpetual conundrum as a user will be "I could do it this way, but there are certainly better ways of doing this, and I have many avenues I could explore, and I don't know which might be fruitful in what timeline".