My take on miniKanren is that it's implementation is designed to be small and hackable. Especially small with microKanren.
If you don't know scheme/lisp, but want to roll your own for educational purposes, then check this out: https://codon.com/hello-declarative-world
Vs Prolog, the emphasis in miniKanren is on constraint programming --- especially writing new constraints to extend it to more problems. Where (chief variants of) Prolog have been optimized in various ways for certain types of problems.
What I read about Datalog is that it is basically a recursive relational database. It's set up for "deductive queries". This wording reminds me of miniKanren --- but the Kanrens are Turing complete.
Ah, Wikipedia has this to say:
In contrast to Prolog, Datalog,
1.) disallows complex terms as arguments of predicates, e.g., p (1, 2) is admissible but not p (f (1), 2),
2.) imposes certain stratification restrictions on the use of negation and recursion,
3.) requires that every variable that appears in the head of a clause also appears in a nonarithmetic positive (i.e. not negated) literal in the body of the clause,
4.) requires that every variable appearing in a negative literal in the body of a clause also appears in some positive literal in the body of the clause[4]
I'd have to put some thought into checking this list against the capabilities of miniKanren. Generally it doesn't ring any bells.
miniKanren is Turing-complete; Datalog deliberately isn't.
Despite that, there are things Datalog can do easily that miniKanren can't. miniKanren can't handle negation natively, but Datalog can (as long as it's stratified, that is, a predicate can't use its own negation).
Datalog is also forward-chaining, so some things that would infinite loop in miniKanren work fine in Datalog - for example, computing the transitive closure of a cyclic graph. If someone added tabling to miniKanren that would solve this.
There's also the question of performance. Some miniKanren implementations are surprisingly fast for what it does, but I suspect they can't compete with, say, Souffle, for the kind of static analysis workloads it's aimed at. Would love to be proven wrong, though.
