(contains-key :a {:v 1 :b 3 :a 3 :g 6})

recursion-contains-key.clj

(boolean (seq (filter #(= k (key %)) m)))

(defn contains-key [m k]
  (loop [[entry & rest :as coll] (seq m)]
    (if (empty? coll)
      false
      (or (= (first entry) k)
          (recur rest)))))

;;first implementation
(defn contains-key [key hashmap]
  (if (= key (first (keys hashmap)))
    true
    (if (empty? (keys hashmap))
      false
      (recur key (rest hashmap))
     )
  )
  )
  
;;second implementation
(defn contains-key [key hashmap]
  (if (= key (first (keys hashmap)))
    true
    (if (empty? (keys hashmap))
      false
      (recur key (rest hashmap))
     )
  )
  )

;;third implementation

defn contains-key [seek-key hashmap]
  (loop [newhashmap hashmap]
    (let [[k, _] (first newhashmap)]    
      (if (= seek-key k)
        true
        (if (nil? k)
          false
          (recur (dissoc newhashmap k))
         )
      )
    )
  )
)