type Person (echo: string -> unit) =
     member it.Echo = echo

type Person =
  new: echo: (string -> unit) -> Person
  member Echo: (string -> unit)

let echo x = printfn "%s" x;;
val echo: x: string -> unit

let person = Person(echo);;
val person: Person

person.Echo "OK";;
//OK
val it: unit = ()