## Baby monads (Depends on lecture notes for safe division by zero.) Write a function `lift'` that generalized the correspondence between + and `add'`: that is, `lift'` takes any two-place operation on integers and returns a version that takes arguments of type `int option` instead, returning a result of `int option`. In other words, `lift'` will have type: (int -> int -> int) -> (int option) -> (int option) -> (int option) so that `lift' (+) (Some 3) (Some 4)` will evalute to `Some 7`. Don't worry about why you need to put `+` inside of parentheses. You should make use of `bind'` in your definition of `lift'`: let bind' (u: int option) (f: int -> (int option)) = match u with None -> None | Some x -> f x;;