Or, you can use explicitly use a reference variable or mutable variable: (# lines are input, - : lines are response) type egg_carton = { mutable eggs: int }

Or, you can use explicitly use a reference variable or mutable variable: (# lines are input, - : lines are response) type egg_carton = { mutable eggs: int } let my_c = { eggs=12 } let breakfast carton = carton.eggs <- carton.eggs - 2 # my_c;; - : egg_carton = {eggs = 12} # breakfast my_c;; - : unit = () # my_c;; - : egg_carton = {eggs = 10} and type food = Pancakes | Eggs let eat f = f := None let short_stack = ref (Some Pancakes) # short_stack;; - : food option ref = { contents = Some Pancakes } # eat short_stack;; - : unit = () # short_stack;; - : food option ref = {contents = None} I think the best part here is that OCaml doesn't use = to assign values, it uses a left arrow (<-) for modifying mutable variables and := for updating what value a reference is pointing to.