Scheme/Lisp IO/case's use

(let ((in (open-input-file "filename"))) (let loop((c (read-char in)))     (case c        ((#\# #\o) 'yes)        ((#\! #\.) 'no)        (else         (loop (read-char in)))))) 读取一个文件当遇到＃,o则停止打印yes,遇到!,.则打印no~!