CODEWITHSUNDEEP
algorithmrecursionscheme
shampouya
shampouya

Reputation: 406

Why do I get an error in Scheme when I try to test for an empty list?

I get this TypeError below that when I run the following code. I think it's because I'm trying to test for an empty list using "null?". Why is that causing an error?

TypeError: Cannot read property 'apply' of undefined [NumberLister, NumberLister, NumberLister, NumberLister, NumberLister, car]

(define NumberLister(lambda(numberList)

(if(null? numberList)
    (= (+ 1 1) 2)
)

(display (car numberList))
(display "\n")
(NumberLister (cdr numberList))
)
)

(NumberLister '(1 3 5 6))

Upvotes: 0

Views: 138

Answers (1)

Óscar López
Óscar López

Reputation: 236004

Normally you can't put more than one expression in the consequent or alternative part of an if expression, if needed group the expressions in a begin form. Also, what's the use of (= (+ 1 1) 2)? just return #t, like this:

(define NumberLister
  (lambda (numberList)
    (if (null? numberList)
        #t
        (begin     
          (display (car numberList))
          (display "\n")
          (NumberLister (cdr numberList))))))

Upvotes: 4

Related Questions