sicp 1.22 的chez scheme 实现.

sicp_1_22_chez.scm

;; 基于 https://cisco.github.io/ChezScheme/csug9.5/csug9_5.pdf 的 12.10. Times and Dates

(define (time-prime-test n)
    (newline)
    (display n)
    (start-prime-test n (current-time))
)

(define (start-prime-test n start-time)
    (if (prime? n)
        (report-prime (time-difference (current-time) start-time))
    )
)

(define (report-prime elapsed-time)
    (display " *** ")
    ; 输出的是纳秒.
    (display (time-nanosecond elapsed-time))
)

(define (search-for-primes n)
    (search-for-primes-counter n 3)
)

(define (search-for-primes-counter n count)
    (if (> count 0)
        (if (even? n)
            (search-for-primes-counter (+ n 1) count)
            ; 知识点: 平级子句, 用 begin 连接.
            (if (prime? n)
                (begin
                    (time-prime-test n)
                    (search-for-primes-counter (+ n 2) (- count 1))
                )
                (search-for-primes-counter (+ n 2) count)
            )
            
            
        )
    )
)

相较 http://community.schemewiki.org/?sicp-ex-1.22 而言, 我的实现, 可以直接求得最终的结果,且不用修改 time-prime-test 的定义.