Can not support "nil"

[StepfenShawn]

(define (filter predicate sequence)
    (cond ((null? sequence) nil)
        ( (predicate (car sequence)) (cons 
        (car sequence) (filter predicate (cdr sequence))) )
        (else (filter predicate (cdr sequence)))
    ))

Then I run it:

> (filter odd? (list 1 2 3 4))
Exception: variable nil is not bound

But I change nil to '(), it's working correctly.

[AiziChen]

Scheme is not Common-Lisp. you can add this line of code before filter procedure:

(define nil '())

[StepfenShawn]

Got it, thanks! @AiziChen