cdr’ing down and almost cons’ing up

• procedure that reverses a list
  (define (reverse p) (if (null? p) nil (append (reverse (cdr p)) (list (car p)))))
  
• procedure that filters out negative numbers
  (define (filterpos p) (if (null? p) nil (let ((e (car p)) (newp (filterpos (cdr p)))) (if (< e 0) newp (cons e newp))))))
  

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