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  • 【SICP练习】142 练习3.77

    练习3-77

    原文

    Exercise 3.77. The integral procedure used above was analogous to the “implicit” definition of the infinite stream of integers in section 3.5.2. Alternatively, we can give a definition of integral that is more like integers-starting-from (also in section 3.5.2):

    (define (integral integrand initial-value dt)
       (cons-stream initial-value            
                    (if (stream-null? integrand)         
                        the-empty-stream           
                        (integral (stream-cdr integrand)                             
                                  (+ (* dt (stream-car integrand))                                
                                     initial-value)                             
                                  dt))))

    When used in systems with loops, this procedure has the same problem as does our original version of integral. Modify the procedure so that it expects the integrand as a delayed argument and hence can be used in the solve procedure shown above.

    代码

     (define (integral delayed-integrand initial-value dt) 
             (cons-stream initial-value 
                     (let ((integrand (force delayed-integrand))) 
                             (if (stream-null? integrand) 
                                     the-empty-stream 
                                     (integral (delay (stream-cdr integrand)) 
                                               (+ (* dt (stream-car integrand)) 
                                                          initial-value) 
                                                    dt))))) 



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  • 原文地址:https://www.cnblogs.com/NoMasp/p/4786058.html
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