As triska says, there are different execution strategies for Prolog and left-recursion is not a problem in practice. To plug my own work, the Inductive Logic Pr

As triska says, there are different execution strategies for Prolog and left-recursion is not a problem in practice. To plug my own work, the Inductive Logic Programming (ILP) system I developed during my PhD (https://github.com/stassa/louise https://github.com/stassa/louise) can learn left-recursive Prolog programs thanks to an inductive Prolog meta-interpreter executed with SLG-resolution (a.k.a. tabling). I mean to say that the inductive meta-interpreter itself is tabled, so it can prove left-recursive programs without entering an infinite recursion (it needs to do that because it learns a program by proving its generalisation). And so it can learn left-recursive programs without "going infinite". That used to be a big problem for ILP, but it's now well and truly solved, in theory as well as in practice. And I say "now" but SLG-resolution is old as a a very old thing; Tamaki and Sato described it in 1986, I believe: https://link.springer.com/chapter/10.1007/3-540-16492-8_66 https://link.springer.com/chapter/10.1007/3-540-16492-8_66 But then implementations took a bit to catch up. >> Prolog is deeply unsuited for work, use Clingo instead. Well, that doesn't make sense. ASP doesn't even allow lists, let alone side-effects (you know, like writing to a stream), so what "work" is it that it's better suited for, than Prolog? Also, if I remember correctly, Clingo is not a language but a grounder? It takes a first-order program and grounds the entire Herbrand base into a set of propositions so that a SAT solver can then derive the stable models of the program? Do I have that wrong? Let me say up front that I've never heard a worse idea in my life, and I've heard a few. First of all, that's why ASP can't use lists, or other functions, because then the Herbrand base goes infinite and good luck grounding it. Second, SAT-solving is NP-complete. As I realised recently (https://news.ycombinator.com/item?id=34072923 https://news.ycombinator.com/item?id=34072923) ASP is an elegant framework for dealing with uncertainty in a purely symbolic manner, with negation as failure and axiomatic, classical negation. But then, why go and mess this elegance up with a dumb propositionalisation approach that loses all the good stuff about first order logic, and that's terminally inefficient to boot? That, I still don't get.