var F_RECOMPUTING = 8; // Currently being recomputed.
var F_QUEUED = 16; // Queued for recomputation.
-var BAD = Tag('BAD') // Used for the value of `bad' deps.
+var BAD = new Tag('BAD'); // Used for the value of `bad' deps.
var DELAYED = []; // Actions delayed by `with_frozen'.
var PENDING = []; // Deps awaiting recomputation.
func = value;
f |= F_QUEUED;
} else {
- val = value;
+ val = value === undefined ? BAD : value;
func = null;
f |= F_VALUE | F_DEPS;
}