Recursively strips values that are nil from a data structure. Will strip entire branches if they recursively evaluate to nil

strip_nil.clj

(defn safe-seq
  [thing]
  (if (seqable? thing)
    (seq thing)
    true))


(defprotocol StripNil
  (strip-nil [data]
             "Recursively strips values that are nil from a datastructure.
              Will strip entire branches if they recursively evaluate to nil"))


(extend-type java.util.Map
  StripNil
  (strip-nil
   [m]
   (let [m-as-vec (vec m)]
     (loop [entry (first m-as-vec)
            remainder (rest m-as-vec)
            collector {}]
       (if-not entry
         collector
         (recur
           (first remainder)
           (rest remainder)
           (let [[k v] entry
                 v (strip-nil v)]
             (if (safe-seq v)
               (assoc collector k v)
               collector))))))))


(extend-type clojure.lang.PersistentList
  StripNil
  (strip-nil
   [coll]
   (let [xf (comp (map strip-nil)
                  (filter safe-seq))]
     (sequence xf coll))))


(extend-type clojure.lang.PersistentVector
  StripNil
  (strip-nil
   [coll]
   (let [xf (comp (map strip-nil)
                  (filter safe-seq))]
     (vec (sequence xf coll)))))


(extend-type nil
  StripNil
  (strip-nil
   [thing]
   thing))


(extend-type java.lang.Object
  StripNil
  (strip-nil
   [thing]
   thing))


;; Test it
;; ##################################
(def t [{:moose-says "blaaargh"
         :giant {:weapon nil}
         :tower nil
         :elf {:can-see "bridge"}
         :elf/thinking-of [{:item/pastry "cake"}
                           {:item/weapon nil}
                           {:location/land "home"}
                           {:location/water nil}]
         :elf/hat [{:actually nil}]}])


(def f [{:id #uuid "2115b649-006f-4159-b820-62450f90b51d"}])


(strip-nil t)

;; => [{:moose-says "blaaargh"
;;      :elf {:can-see "bridge"}
;;      :elf/thinking-of [{:item/pastry "cake"}
;;                        {:location/land "home"}

;; Before safe-empty?
(strip-nil f)

;; => IllegalArgumentException Don't know how to create ISeq from: java.util.UUID
;;    clojure.lang.RT.seqFrom (RT.java:550)


;; After safe-empty?
(strip-nil f)

;; => [{:id #uuid "2115b649-006f-4159-b820-62450f90b51d"}]

(safe-empty? (java.util.UUID/randomUUID))

;; => false