Updating Variables [Harlowe]

I am having trouble updating my variables. This is what I have so far:

Here you can rest, eat, or reassess your inventory.

{(set: $days to 0)
Rest(click: "Rest")[(set: $days to $days + 1)]}

Day $days

but this is what happens when I click "Rest":


Here you can rest, eat, or reassess your inventory.

Day 0


Is there something I'm missing?