This macro was somewhat useful when I was implementing static analysis for a compiler with core.logic.
(defmacro ==>> (link: expr-in & rel-forms)
"Thread the expr-in through rel-forms then unify with last rel-forms
(the 'out expression').
(==>> (link: ) (firsto) (firsto) x))
;; 'x' will become bound to value 1
This macro expands to:
(fresh (link: _A _B)
(firsto (link: ) _A)
(firsto _A _B)
(== _B q))
If you imagine that the 'return value' of firsto is its last parameter,
then it works just like clojure.core/-> as return value of each form is
first argument of the following form."