SICP 問題 2.20
(define (same-parity x . y) (define (recur lis pred?) (cond ((null? lis) nil) ((pred? (car lis)) (cons (car lis) (recur (cdr lis) pred?))) (else (recur (cdr lis) pred?)))) (cons x (recur y (if (odd? x) odd? even?))))
gosh> (same-parity 1 2 3 4 5 6 7) (1 3 5 7) gosh> (same-parity 2 3 4 5 6 7) (2 4 6)
ググるといろんなやり方でみんな解いてますね.