+(defvar *generation* (list '*generation*)
+ "Generation marker, used to remember when we last updated a particular dep.
+ Essentially, if the dep's generation matches *GENERATION* then it doesn't
+ need updating again.")
+
+(defvar *evaluating-dep* nil
+ "The dep currently being evaluated. This is bound only during the call of
+ a value-func, and is used to track the dependencies implied during the
+ function's evaluation.")
+
+(defvar *pending-deps* nil
+ "A queue of deps pending recomputation. This is bound to a queue during
+ recomputation and restored afterwards, so it can also be used as a flag to
+ detect whether recomputation is happening.")
+