- -弄明白的时候 很爽很爽
运行环境 DrRacket

#lang planet neil/sicp
(define zero
(lambda (f) (lambda (x) x)))
(define (add-1 n)
(lambda (f) (lambda (x) (f ((n f) x)))))
(define one
(lambda (f) (lambda (x) (f x))))
(define two
(lambda (f) (lambda (x) (f (f x)))))
(define (add m n)
(lambda (f)
(lambda (x)
((m f) ((n f) x)))))
; 怎么检验啊= =
; 啊！“对0应用n次后继函数”=n ~
(define (to-num n)
(define (suc x) (+ 1 x))
((n suc) 0))
(to-num zero)
(to-num one)
(to-num two)
(to-num (add-1 two))
(to-num (add two two))