chickadee » srfi-14 » char-set-fold

This is the fundamental iterator for character sets. Applies the function KONS across the character set CS using initial state value KNIL. That is, if CS is the empty set, the procedure returns KNIL. Otherwise, some element C of CS is chosen; let CS' be the remaining, unchosen characters. The procedure returns

(char-set-fold KONS (KONS C KNIL) CS')

Examples:

;; CHAR-SET-MEMBERS
(lambda (cs) (char-set-fold cons '() cs))
 
;; CHAR-SET-SIZE
(lambda (cs) (char-set-fold (lambda (c i) (+ i 1)) 0 cs))
 
;; How many vowels in the char set?
(lambda (cs) 
  (char-set-fold (lambda (c i) (if (vowel? c) (+ i 1) i))
                 0 cs))