Clojure macro for executing code if a library exists

require-me-maybe.clj

(defmacro when-require [n & body]
  (let [nn (eval n)]
    (try (require nn)
      (catch Throwable e nil))
    (when (find-ns nn)
      `(do ~@body))))


(defmacro if-require [n body1 body2]
  (let [nn (eval n)]
    (try (require nn)
      (catch Throwable e nil))
    (if (find-ns nn)
      `(do ~body1)
      `(do ~body2))))


; Usage example:
; 
; (when-require 'immutant.messaging
;   (immutant.messaging/start "topic.whatever")
;   (immutant.messaging/publish "topic.whatever" "hi"))
;