y = x + 1 is not dealing with state. Supposing there was a desire to have x = x + 1, the simple way of doing this is x = x + 1, and the complicated way is to do

y = x + 1 is not dealing with state. Supposing there was a desire to have x = x + 1, the simple way of doing this is x = x + 1, and the complicated way is to do world = Increment(x, world).