Exercise 2.35. Redefine count-leaves from section 2.2.2 as an accumulation:
(define (count-leaves t)
(accumulate <??> <??> (map <??> <??>)))
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| (define nil '()) | |
| (define (accumulate op initial sequence) | |
| (if (null? sequence) | |
| initial | |
| (op (car sequence) | |
| (accumulate op initial (cdr sequence))))) | |
| (define (enumerate-tree tree) | |
| (cond | |
| ((null? tree) | |
| nil) | |
| ((not (pair? tree)) | |
| (list tree)) | |
| (else | |
| (append | |
| (enumerate-tree (car tree)) | |
| (enumerate-tree (cdr tree)))))) | |
| (define (count-leaves t) | |
| (accumulate | |
| + | |
| 0 | |
| (map | |
| (lambda (x) | |
| (if | |
| (pair? x) | |
| (count-leaves x) | |
| 1)) | |
| t))) | |
| (define tree (list 1 (list 2 (list 3 4)) 5 6 7 8)) | |
| (count-leaves tree) ;; => 7 | |
| (count-leaves (list 1 (list 2 (list 3 4)) 5)) | |