《Chez Scheme初探》定义变量、递归、测试性能、并列代码编写

普通fib函数

(define (fact n) (if (= n 1) 1
                             (* n (fact (- n 1))  )
                 )
)

尾递归fib函数

(define (fact-tail n) (fact-rec n n))
(define (fact-rec n p) (if (= n 1) p
                                   (let ( (m (- n 1)) )
                                        (fact-rec m (* p m))
                                   )
                       )
)

性能测试

(let ([a 120000]) (begin (time (begin (fact a) (+ 30 3) )) (time (begin (fact-tail a) (+ 30 3) ))))

测试结果：

(time (begin (fact a) ...))
    115 collections
    11.843750000s elapsed cpu time, including 0.031250000s collecting
    11.867882300s elapsed real time, including 0.040223800s collecting
    13241981264 bytes allocated, including 13012956832 bytes reclaimed
(time (begin (fact-tail a) ...))
    229 collections
    9.796875000s elapsed cpu time, including 0.062500000s collecting
    9.816385400s elapsed real time, including 0.084685200s collecting
    14538387792 bytes allocated, including 14538258416 bytes reclaimed
33

机器：

CPU：i7-8550U  内存24GB