Exercise 1.30. The sum procedure above generates a linear recursion. The procedure can be rewritten so that the sum is performed iteratively. Show how to do this by filling in the missing expressions in the following definition:
(define (sum term a next b)
(define (iter a result)
(if
(iter )))
(iter ))
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(define (inc n) (+ n 1)) | |
(define (identity x) x) | |
(define | |
(sum-iter-helper | |
runningsum | |
termfunction | |
termvalue | |
nextfunction | |
upperbound) | |
(if | |
(> termvalue upperbound) | |
runningsum | |
(sum-iter-helper | |
(+ runningsum (termfunction termvalue)) | |
termfunction | |
(nextfunction termvalue) | |
nextfunction | |
upperbound))) | |
(define (sum term a next b) | |
(sum-iter-helper | |
0 | |
term | |
a | |
next | |
b)) | |
(define (sum-integers a b) | |
(sum identity a inc b)) | |
(sum-integers 1 10) | |