PostgreSQL-Prolog: A Prolog library to connect to PostgreSQL databases

Not directly, no -- it's at least part of my own musings on logical systems. Probably the closest thing in my mind is Kuper et al.'s LVars, and I've long wanted to extend its join-semilattices to meets, but I left academia for a rather demanding day job ^_^;

I do think consensus algorithms have something deeply in common here, as CALM (Consistency As Logical Monotonicity) seems to cover the space of join-semilattice structures pretty crisply, and CALM is all about when you don't need consensus. But again, just my own musings.

The key innovation of Scryer Prolog in this respect is that the system internally, i.e., within Rust, represents each string as a sequence of raw bytes (UTF-8 encoded, 0-terminated), and to Prolog programs, the string appears as if it were a list of characters (i.e., atoms of length 1). So, no conversion is necessary at all: The compact internal representation is used whenever possible, and Prolog programs only see lists of characters all of the time, making common predicates such as append/3 and length/2, and most importantly DCGs, automatically usable for reasoning about strings.

For example, the string "abc" takes only 4 bytes in this representation, and the unification "abc" = [a,b,c] succeeds. Indeed, we have:

    ?- write_canonical("abc").
    '.'(a,'.'(b,'.'(c,[])))   true.

On 64-bit systems, a conventional internal representation of "abc" as the compound term .(a, .(b, .(c, []))) takes 8 bytes per functor (each '.'/2 takes 8 bytes, i.e., 1 cell in the WAM), 8 bytes per character (as a pointer to the atom table, again 1 cell in the WAM), and 8 bytes for each tail. All Prolog systems before Scryer Prolog use 16 to 24 times as much memory to represent a list of characters. As of recent, Trealla Prolog also uses the efficient representation, at least for fully instantiated strings. Scryer Prolog can also represent partial strings such as [a,b,c|Ls] with the efficient encoding.