Unicodeで遊ぶ http://d.hatena.ne.jp/rahaema/20130622/p1 をgaucheで

ab2maru.scm

(use srfi-13)
(use srfi-14)

(define (ab->maru str)
  (string-map
   (^c (let1 i (char->integer c)
         (integer->char
          (cond ((char-set-contains? #[a-z] c)
                 (+ (- i (char->integer #\a)) #x24d0))
                ((char-set-contains? #[A-Z] c)
                 (+ (- i (char->integer #\A)) #x24b6))
                (else i)))))
   str))

(print (ab->maru "Masahide Maehara"))
;; => Ⓜⓐⓢⓐⓗⓘⓓⓔ Ⓜⓐⓔⓗⓐⓡⓐ