(defvar age-name '((27 Jonah)
                   (18 Alan)
                   (28 Glory)
                   (18 Popeye)
                   (28 Alan)))

(defvar nemesis-name '((Jonah Whales)
                       (Jonah Spiders)
                       (Alan Ghosts)
                       (Alan Zombies)
                       (Glory Buffy)))

(defun hash-join (left left-key right right-key)
  (let ((join-hash [group-by left-key left])) ;; hash phase
    (append-each ((r-entry right))            ;; join phase
      (collect-each ((l-entry [join-hash [right-key r-entry]]))
        ^(,l-entry ,r-entry)))))

(format t "~s\n" [hash-join age-name second nemesis-name first])