churchnumeral.hy

(eval-and-compile
  ; pretty print utility
  (defn lprint [expr]
    (if (coll? expr)
        (+ "(" (.join " " (list-comp (lprint x) [x expr])) ")")
        (str expr)))
  ; church number body generator: (N 3 m n) ; -> (m (m (m n)))
  (defn N [n x y]
    (if (zero? n) y
        (+ (% "(%s " x) (N (dec n) x y) ")"))))
; lambda expression
(defmacro L [&rest expr] (lprint expr))
; church number generator: (NUM 3) ; -> (L x y , (x (x (x y))))
(defmacro NUM [n &optional [x "x"][y "y"]]
  `(L ~x ~y , ~(read_str (N n x y))))

To define L: (defmacro L [&rest expr] (lprint expr))
To define lprint: (defn lprint [expr] ...)