23 hours ago
my attempt to do the exercises in sicp.
Sunday, June 29, 2008
sicp exercise 1.32
; Exercise 1.32. a. Show that sum and product (exercise 1.31) are both special cases of a still more
; general notion called accumulate that combines a collection of terms, using some general accumulation
; function:
;
; (accumulate combiner null-value term a next b)
;
; Accumulate takes as arguments the same term and range specifications as sum and product, together
; with a combiner procedure (of two arguments) that specifies how the current term is to be combined
; with the accumulation of the preceding terms and a null-value that specifies what base value to use
; when the terms run out. Write accumulate and show how sum and product can both be defined as simple
; calls to accumulate.
; b. If your accumulate procedure generates a recursive process, write one that generates an
; iterative process. If it generates an iterative process, write one that generates a recursive process.
(define (accumulate-recur combiner null-value term a next b)
(if (> a b)
null-value
(combiner (term a) (accumulate-recur combiner null-value term (next a) next b))))
(define (accumulate-iter combiner null-value term a next b)
(define (iter a result)
(if (> a b)
result
(iter (next a) (combiner (term a) result))))
(iter a null-value))
(define (sum term a next b)
(accumulate + 0 term a next b))
(define (product term a next b)
(accumulate * 1 term a next b))
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