They're called "thrush" operators, and they translate that code to this: (defn ping [] (:content (http/get "http://localhost:5123" :as :string)))

They're called "thrush" operators, and they translate that code to this: (defn ping [] (:content (http/get "http://localhost:5123" :as :string))) (defn multi-ping [] (apply str (repeatedly 16 #(ping))) More examples: http://debasishg.blogspot.com/2010/04/thrush-in-clojure.html http://debasishg.blogspot.com/2010/04/thrush-in-clojure.html