sicp2-20.scm

; Exercise 2.20
(define (same-pair x . b)
  (define (is-same-parity? x y)
    (or (and (even? x) (even? y))
        (and (odd?  x) (odd?  y))))
  (define (same-pair-recur items)
    (if (null? items)
        '()
        (if (is-same-parity? x (car items))
            (cons (car items) (same-pair-recur (cdr items)))
            (same-pair-recur (cdr items)))))
  (cons x (same-pair-recur b)))