Numbers in Lambda Calculus

number-lambda.cljs

(defn v [x]
  (list 'λ x))

(defn view [n] ((n v) 'x))

(deftype LambdaNum [n]
  Object
  (toString [this] (str (view this)))
  (equiv [this other] (-equiv this other))
  
  IPrintWithWriter
  (-pr-writer [o writer _] (-write writer (view o)))
  
  IEquiv
  (-equiv [this other]
     (if (instance? LambdaNum other)
       (= (view this) (view other))
       false))
  
  IFn
  (-invoke [this f]
           (fn [x]
             ((apply comp (repeat n f)) x))))


(def two (LambdaNum. 2))
(def another-two (LambdaNum. (+ 1 1)))
(def zero (LambdaNum. 0))

[zero
 two
 (str two)
 (= two two)
 (= two another-two)
 (= two three)]