eval expr2 ((c, value) :: g) s'
...
+Similarly:
+
+ ...
+ | Addition (expr1, expr2) ->
+ let (value1, s') = eval expr1 g s
+ in let (value2, s'') = eval expr2 g s'
+ in (value1 + value2, s'')
+ ...
+
Let's consider how to interpet our new syntactic forms `newref`, `deref`, and `setref`: