+(defun set-default-shape (breed shape)
+ "SET-DEFAULT-SHAPE BREED SHAPE => RESULT
+
+ARGUMENTS AND VALUES:
+
+ BREED: a valid breed
+ SHAPE: a string
+ RESULT: undefined
+
+DESCRIPTION:
+
+ Specifies a default initial shape for a BREED. When a turtle, or it changes breeds,
+ its shape is set to the given shape.
+
+ SET-DEFAULT-SHAPE doesn't affect existing agents, only agents you create afterwards.
+
+ See http://ccl.northwestern.edu/netlogo/docs/dictionary.html#set-default-shape"
+ (when (not (breed-p breed)) (error "Need a valid breed"))
+ (setf (breed-default-shape breed) shape))
+