RosettaCodeData/Task/Hash-join/TXR/hash-join.txr

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(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])