(pred v f)
Check a predicate against the value logic var. Non-relational.
user> (run* [q] (pred q symbol?))
()
user> (run* [q] (== q 'x) (pred q symbol?))
(x)
user> (run* [q] (== q 1) (pred q symbol?))
()
user> (run* [q] (== q 1) (pred q number?))
(1)