A WhizzML version of Clojure's merge-with

merge-with.whizzml

(define (merge-with* fn m1 m2)
  (reduce (lambda (result key)
            (let (v1 (get m1 key)
                  v2 (get m2 key))
              (assoc result key (if (and v1 v2)
                                  (fn v1 v2)
                                  (or v1 v2)))))
          {}
          (concat (keys m1) (keys m2))))

(define (merge-with fn . ms)
  (reduce (lambda (result m) (merge-with* fn result m))
          (head ms)
          (tail ms)))

;; whizzml> (merge-with + {"a" 3 "c" 1} {"b" 4 "a" 3 "c" 2} {"c" 8})
;; {"a":6,"c":11,"b":4}