Sort of nice nil checker in Clojure

die-on-nils.clj

(defn- ellipses-if-long
  "Append \"...\" to string version of x if x's length exceeds n."
  ([x] (ellipses-if-long x 50))
  ([x n]
   (assert (pos? n) "n must be positive")
   (let [s (str x)]
     (if (> (.length s) n)
       (str (subs s 0 n) "...")
       s))))

(defmacro non-nil!
  "If any of exprs evaluates to nil throw an exception containing a snippet of
  the offending code in the message. Returns nil when it doesn't throw. Note
  that each of exprs (until one evaluates to nil) will be evaluated here, so
  don't use with side-effecting expressions."
  [& exprs]
  `(do
     ~@(for [expr exprs]
         `(when (nil? ~expr) ; expr is actually evaluated here
            (throw
              (ex-info (format "'%s' evaluated to nil"
                               (ellipses-if-long '~expr))
                       {:expr '~expr}))))
     nil))