This works fine for some time, but then I start getting an exception saying: "No implementation of method: :search of protocol: #'some.thing/ISearchEngine found for class: some.thing.SearchEngine"

protocols.clj

(defprotocol ISearchEngine
  "Search the web"
  (search [engine term] "Search the web for a single (one-word) term."))


(defrecord SearchEngine [url]
  ISearchEngine
  (search [this term]
    (-> (str (:url this) term)
        http/get deref :body)))


(defonce google
  (SearchEngine. "https://www.google.co.in/search?q="))

(defonce bing
  (SearchEngine. "https://www.bing.com/search?q="))

(defonce ddg
  (SearchEngine. "https://duckduckgo.com/?q="))


(search google "wonko+the+sane")