(def asym-hobbit-body-parts [{:name "head" :size 3}
                             {:name "left-eye" :size 1}
                             {:name "left-ear" :size 1}
                             {:name "mouth" :size 1}
                             {:name "nose" :size 1}
                             {:name "neck" :size 2}
                             {:name "left-shoulder" :size 3}
                             {:name "left-upper-arm" :size 3}
                             {:name "chest" :size 10}
                             {:name "back" :size 10}
                             {:name "left-forearm" :size 3}
                             {:name "abdomen" :size 6}
                             {:name "left-kidney" :size 1}
                             {:name "left-hand" :size 2}
                             {:name "left-knee" :size 2}
                             {:name "left-thigh" :size 4}
                             {:name "left-lower-leg" :size 3}
                             {:name "left-achilles" :size 1}
                             {:name "left-foot" :size 2}])

(defn needs-matching-part?
  [part]
  (re-find #"^left-" (:name part)))

(defn make-matching-part
  [part]
  {:name (clojure.string/replace (:name part) #"^left-" "right-")
   :size (:size part)})

(defn symmetrize-body-parts
  "Expects a seq of maps which have a :name and :size"
  [asym-body-parts]
  (loop [remaining-asym-parts asym-body-parts
         final-body-parts []]
    (if (empty? remaining-asym-parts)
      final-body-parts
      (let [[part & remaining] remaining-asym-parts
            final-body-parts (conj final-body-parts part)]
        (if (needs-matching-part? part)
          (recur remaining (conj final-body-parts (make-matching-part part)))
          (recur remaining final-body-parts))))))

(symmetrize-body-parts asym-hobbit-body-parts)