[scheme][Gauche]for-each, tree-walk, reverse-tree-walk

「プログラミングGauche」P.64～ 66 7.2 手続きを取る手続き

ようは高階関数ということで。foldも高階関数ですね。

 

 

for-eachを試してみる。

(for-each (lambda (n) (print (* n n))) '(1 2 3 4 5)) ;; => gosh> 1 ;; => 4 ;; => 9 ;; => 16 ;; => 25 ;; => #<undef>

 

 

tree-walk写経。

;; tree-walk (define (tree-walk tree walker proc)   (walker (lambda (ele)         (if (list? ele)         (tree-walk ele walker proc)         (proc ele)))       tree))   (tree-walk '(1 (2 3 (4 5 6)) 7 8 9 (10 (11 (12)))) for-each print) ;; => gosh> 1 ;; => 2 ;; => 3 ;; => 4 ;; => 5 ;; => 6 ;; => 7 ;; => 8 ;; => 9 ;; => 10 ;; => 11 ;; => 12 ;; => #<undef>

 

listを反転させるreverse。

;; reverse (define (reverse ls)   (define (rev-iter ls ret)     (if (null? ls)     ret     (rev-iter (cdr ls)(cons (car ls) ret))))   (rev-iter ls '()))   (reverse '(1 2 3 4 5)) ;; => (5 4 3 2 1)

 

 

listを反転後にfor-eachするreverse-for-each。

;; reverse-for-each (define (reverse-for-each proc ls)   (for-each proc (reverse ls)))   (reverse-for-each print '(1 2 3 4 5)) ;; => gosh> 5 ;; => 4 ;; => 3 ;; => 2 ;; => 1 ;; => #<undef>

 

tree-walkにreverse-for-eachとprintを渡してみる。
今気づいたけど、本に書いてあるコードと引数の順番違う。

(tree-walk '(1 (2 3 (4 5 6)) 7 8 9 (10 (11 (12)))) reverse-for-each print) ;; => gosh> 12 ;; => 11 ;; => 10 ;; => 9 ;; => 8 ;; => 7 ;; => 6 ;; => 5 ;; => 4 ;; => 3 ;; => 2 ;; => 1 ;; => #<undef>