To those who have used Prolog, is the description sufficient to know what it does and if it will be useful? I've never use prolog and I don't know the lingo.
Someone on Mercury's mailing list took pity on me, and told me to just straight up try some Prolog.
Prolog, at least the basics, isn't hard at all, and it takes maybe a day to get you to write something that works. Of course, every language has its inconsistencies, dark corners and unexpected turns, and, sometimes some very deep and general pieces of wisdom that aren't on the surface. But, really, if you want to understand any Prolog derivative, the best way I can think about, is to learn some Prolog. It's the most efficient way to the goal. It doesn't really take long.
But I do agree that being familiar with Prolog is a big help in understanding what Souffle is. For a quick intro to Prolog, I recommend this video[2], which speaks from a "industry practical" point of view, and introduces concepts that almost all apply to Datalog :)
[0] https://souffle-lang.github.io/simple
[1] https://souffle-lang.github.io/tutorial
[2] https://twitter.com/ThePrologClause/status/15006425339400233...
But, other visions of programming have coexisted with this main educational vortex, including logic programming like Prolog. Actually, if you have heard of any of these alternates, you have probably heard of functional programming, which can be ahistorically understood as saying “hey these locks and races and all that, it's actually very complicated, maybe we could have a simpler model of programming for 90% of our work and only break out the Java when we really need it.” And you’re like “what will you replace it with?” and they respond “Template substitutions! It's all the power of lexicographic scopes, all the power of looping (via recursion), but when you want to express the really complex stuff you need templates that have side effects when substituted, we can give those scary names.” So you give me a sunbeam and a raincloud and I give you back a rainbow.
If that's the functional programming idea then logic programming takes the same idea but adds unification and search. The idea is “ok but why do I have to fill in all the parameters to a template before I use it? I should just say “if light shines on a droplet-cloud it makes a rainbow, a sunbeam is a light, a raincloud is a droplet-cloud, hey language, what are all the things that make a rainbow?”
Functional programming was based on the function, the template, the “I take these args and produce a structure looking like such-and-so.” Logic programming is based on the Horn clause, “X verbs Y, for some entities X and Y that I maybe know about and some verb that I am being introduced to.”
Basic things that logic programming does very well, OOP kind of struggles with. You can kind of understand this if you have written a SQL query. The verbs can be thought of as tables that foreign-key to X and to Y, if you want to write OOP to solve a logic puzzle you have to choose explicit ways to search or brute force... SQL DBs come with B-trees and indexes to solve a lot of these problems. Whereas with Prolog you just write the pattern to match and the new pattern to emit.
It's a rather different take on what the building blocks should be.
That said, Souffle is touring complete due to its adding of constructors to the language.
Moreover, using various forms of coinduction you can encode infinite computation even in non-TC languages.