$ swipl
    ?- X = 10.
    X = 10.

    $ gprolog
    | ?- X = 10.
    X = 10
    yes

(a) The REPL should print the variable bindings which caused the query to succeed. (b) The query `X = 10.` should succeed trivially.

I've been using Prolog on-and-off for close to a decade now and have implemented my own pseudo-Prolog (also in Javascript; was missing logic variables and extra-logical builtins). I tried to get pretty much any query to succeed in this interpreter and couldn't. This is not any kind of Prolog that I'm familiar with.