(defvar *ticks* nil)
(defvar *breeds* nil)
+(define-condition stop nil nil)
+
+(defmacro with-stop-handler (&rest forms)
+ "MACRO WITH-STOP-HANDLER &rest FORMS => HANDLED-FORM
+
+ARGUMENTS AND VALUES:
+
+ FORMS: body to be handled
+ HANDLED-FORM: body with handling
+
+DESCRIPTION:
+
+ WITH-STOP-HANDLER is a convenience macro to handle when
+ programs issue a stop condition. When one does, a simple
+ :stop is returned."
+ `(handler-case (progn ,@forms) (stop (s) :stop)))
+
(defstruct turtle who color heading xcor ycor (label "") (label-color 9.9d0) (size 1d0) shape)
(defstruct patch color xcor ycor)