named-letの練習。 空白文字はカウントしない。

str-count.scm

(define (str-count str)
  (let loop ((ls (string->list str))
	     (count 0))
    (let ((c (if (pair? ls)
		 (car ls)
		 ls))
	  (inc (lambda (x) (+ x 1))))
      (cond
       ((null? ls) count)
       ((char-whitespace? c) (loop (cdr ls) count))
       (else
	(loop (cdr ls) (inc count)))))))

;; Stringで受け取った数値文字列を数値のリストとして扱いたい
(define (string->int-list str)
  (let loop ((char-list (string->list str))
	     (acc '()))
    (cond
     ((null? char-list) (reverse acc))
     (else (let ((c (car char-list))
		 (c2i (lambda (x) (- x 48))))
	     (loop (cdr char-list)
		   (cons (c2i (char->integer c)) acc)))))))