CCResult.InfixMonadic composition. e >>= f proceeds as f x if e is Ok x or returns e if e is an Error.
a <*> b evaluates a and b, and, in case of success, returns Ok (a b). Otherwise, it fails, and the error of a is chosen over the error of b if both fail.
Let operators on OCaml >= 4.08.0, nothing otherwise
include CCShimsMkLet_.S2 with type ('a, 'e) t_let2 := ('a, 'e) result