(cond [(empty? xs) 0] [(= x (first xs)) (add1 (count-them (rest xs) x))] [else (count-them (rest xs) x)])) I have begun a refactoring of the f

Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
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Consider this code. It counts how many x's are in xs. It is not tail recursive because not all recursive calls terminate the function. (The middle branch of the cond does an add1 after the recursive call.)

(define (count-them xs x)
(cond [(empty? xs) 0]
[(= x (first xs)) (add1 (count-them (rest xs) x))]
[else (count-them (rest xs) x)]))

I have begun a refactoring of the function to make it tail-recursive using an accumulator. Complete the code. To make it easier I have done some of the work for you. You need only replace each ??? with an expression.

Your solution must only modify the ??? spaces and leave the rest alone.

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