gistfile1.txt

(define (filter pred xs)
  (define (skip xs)
    (cond [(null? xs) xs]
          [(pred (car xs)) xs]
          [else (skip (cdr xs))]))
  (unfold (^[xs] (null? (skip xs)))
          (^[xs] (car (skip xs)))
          (^[xs] (cdr (skip xs)))
          xs))