open recursive ack

open-ack.rkt

#lang racket/base

(require "../main.rkt")

(define (open-ack m n rec)
  (cond [(zero? m) (+ 1 n)]
        [(zero? n) (rec (- m 1) 1)]
        [else (rec (- m 1) (rec m (- n 1)))]))

(define close
  (terminating-function/c
   (λ (f)
     (λ (m n)
       (f m n (close f))))))

(define ack (terminating-function/c (close open-ack)))