common-lisp 简单的LOOP表格
示例
没有特殊关键字的简单LOOP表单：
(loop forms...)
为了打破循环，我们可以使用(return<returnvalue>)`
一些例子：
(loop (format t "Hello~%")) ; prints "Hello" forever
(loop (print (eval (read)))) ; your very own REPL
(loop (let ((r (read)))
(typecase r
(number (return (print (* r r))))
(otherwise (format t "Not a number!~%")))))