Constructing the arithmetic only with functions. This gist is used by articles inside blog.klipse.tech. Be careful not to break the articles.

lambda_calculus.cljs

(defn visual [x]
  (list 'f x))

(defn view [f]
  ((f visual) 'x))

(deftype Lambda [f]
  Object
  (toString [_] (str (view f)))

  IPrintWithWriter
  (-pr-writer [this writer _] (-write writer (str (view f))))
  
   IEquiv
  (-equiv [this other]
          (= (view this) (view other)))

  IFn
  (-invoke [this g]
           (f g)))
         
(defmacro lambda [name args & body]
  `(defn ~name ~args (Lambda. ~@body)))

(lambda numeral [n]
    (fn [f]
      (fn [x]
        ((apply comp (repeat n f)) x))))