Check if the item in list or sub-list

问题

I want to use the check function to check if the item is in the list or the sub-list. But the error really confuse me. Can someone tell me what's wrong with my code?

(define check
 (lambda(item lis)
  (cond((null? lis) #f)
       (else(if(pair? (car lis)) 
               (if(check item (car lis)) #t (check item (cdr lis))) 
               (if(equal? item (car list)) #t (check item (cdr lis))))))))


> (check 'a '(a b))
. . car: contract violation
  expected: pair?
  given: #<procedure:list>

回答1:

You have a typo in here:

(equal? item (car list))

It should be:

(equal? item (car lis))

Notice that list is a procedure, and the parameter in your code is called lis.

来源：https://stackoverflow.com/questions/19436282/check-if-the-item-in-list-or-sub-list