Blog.GuestList.Lenses.Examples.fs

// A lens that provides the name of the guest.
let name_ : ResultLens<Guest, string> =
  (fun g -> Ok g.Name), (fun n _ -> Guest.create n)

// A lens on the guest list that provides the individual guests on the list.
let guests_ : ResultLens<GuestList, Guest list> =
  (fun (GuestList xs) -> Ok xs), fun xs _ -> GuestList.create xs

// A lens that points to a single guest on the guest list.
let guest_ name : ResultLens<GuestList, Guest> =
  guests_ >=> List.single_ (fun { Name = n } -> n = name)