; ======================================================================
;
; Structure and Interpretation of Computer Programs
; (trial answer to excercises)
;
; 计算机程序的构造和解释(习题试解)
;
; created: code17 08/19/05
; modified:
; (保持内容完整不变前提下，可以任意转载)
; ======================================================================
;; SICP No.2.40
(define (unique-pairs n)
(flatmap (lambda (i)
(map (lambda (j) (list i j))
(enumerate-interval 1 (- i 1))))
(enumerate-interval 1 n)))
(define (prime-sum-pairs n)
(map make-pair-sum (filter prime-sum? (unique-pairs n))))
;; Test-it:
;; Welcome to MzScheme version 209, Copyright (c) 2004 PLT Scheme, Inc.
;; > (prime-sum-pairs 10)
;; ((2 1 3) (3 2 5) (4 1 5) (4 3 7) (5 2 7) (6 1 7) (6 5 11) (7 4 11) (7 6 13) (8 3 11) (8 5 13) (9 2 11) (9 4 13) (9 8 17) (10 1 11) (10 3 13) (10 7 17) (10 9 19))