11. The system of claim 10 , wherein the instructions further comprise instructions for: determining that every stack in a plurality of stacks is in a blocked state or a completed state.
11. The system of claim 10 , wherein the instructions further comprise instructions for: determining that every stack in a plurality of stacks is in a blocked state or a completed state. 12. The system of claim 11 , wherein the instructions further comprise instructions for: prior to determining that every stack in a plurality of stacks is in a blocked state or completed state, identifying expressions for batch evaluation in one or more stacks of the plurality of stacks that is in an unblocked state; transitioning a state of each stack of the plurality of stacks that is in an unblocked state to a blocked state.