使用lambda的方案(scheme using lambda)

 我在方案中有一段使用几个lambdas的代码。 它基本上返回一个中间的数字。 
 
(define foo
  (lambda (x)
    (letrec
      ((h (lambda (y z)
        (cond
          ((null? y) 'undefined)
          ((null? (cdr y)) (car z))
          (else (h (cddr y) (cdr z)))))))
  ((lambda (y) (h y y)) x))))
 
 我必须重写代码，所以它不使用任何lambda。 我怎么做？ 

I have a piece of code in scheme that uses several lambdas. It basically returns a number that's in the middle. 
 
(define foo
  (lambda (x)
    (letrec
      ((h (lambda (y z)
        (cond
          ((null? y) 'undefined)
          ((null? (cdr y)) (car z))
          (else (h (cddr y) (cdr z)))))))
  ((lambda (y) (h y y)) x))))
 
I have to rewrite the code so it doesn't use any lambda. How do I do that?

原文：https://stackoverflow.com/questions/10860734