fable functor

functor.fs

type Functor = class end

let inline map (f: 'a -> 'b) (x: ^Functor) : ^Result =
    ((^Functor or ^Result or Functor) : (static member Map : ^Functor * ('a -> 'b) -> ^Result) (x, f))

type Functor with
    static member inline Map (x: list<'a>, f: 'a -> 'b) : list<'b> =
        List.map f x

    static member inline Map (x: option<'a>, f: 'a -> 'b) : option<'b> =
        Option.map f x

let inline replace (value: 'a) (x: ^Functor) : ^Result =
    map (fun _ -> value) x

// Usage Examples
let resultList = replace 42 [1; 2; 3]
// resultList : int list = [42; 42; 42]

let resultOption = replace "hello" (Some 5)
// resultOption : string option = Some "hello"
printf "%A" resultOption
printf "%A" resultList