Immutable hashmap implemented as a Clojure macro

hmap.clj

(ns hmap)

(defmacro hmap [& kvs]
  "Returns an immutable hashmap.
   Keys must be compile-time constants."
  (if (even? (count kvs))
    (let [tups (partition 2 kvs)
          keys (mapv first tups)
          kvs+ (concat kvs [::keys keys])]
      `(fn [k#]
         (case k# ~@kvs+)))
    (throw (Exception. "hmap takes an EVEN number of args"))))


(comment
  (def m (hmap :a 1 :b 2))
  ;; => #'hmap/m
  (m ::keys)
  ;; => [:a :b]
  (m :a)
  ;; => 1
  (m :c)
  ;; => IllegalArgumentException No matching clause: :c
  )