actually - I'm talking about a function expression. Think about a spreadsheet with a formula similar to "=SUM(A1+B1)". What this means is that when A1 or B1 cha

actually - I'm talking about a function expression. Think about a spreadsheet with a formula similar to "=SUM(A1+B1)". What this means is that when A1 or B1 change.. then this formula result should get re-computed. Remember that A1 and B1 themselves may be computed results... what happens today is that I need to recompute ALL formulas - because there is no easy way to know which formulas changed.