+(defun read-integer (string)
+ (let ((sign 1)
+ (number nil)
+ (size (length string)))
+ (dotimes (i size)
+ (let ((elt (char string i)))
+ (cond
+ ((digit-char-p elt)
+ (setq number (+ (* (or number 0) 10) (digit-char-p elt))))
+ ((zerop i)
+ (case elt
+ (#\+ nil)
+ (#\- (setq sign -1))
+ (otherwise (return-from read-integer))))
+ ((and (= i (1- size)) (char= elt #\.)) nil)
+ (t (return-from read-integer)))))
+ (and number (* sign number))))
+