They are analogous if you represent side effects like this: new_state = f(old_state, x) then an idempotent operation is f(f(state, x), x) == f(state,

They are analogous if you represent side effects like this: new_state = f(old_state, x) then an idempotent operation is f(f(state, x), x) == f(state, x) In the context of drawing windows: draw(draw(fbuf, wnd, x, y), wnd, x, y) == draw(fbuf, wnd, x, y) but this is of course false if you allow alpha channel transparency...