stream_sample.ml

module Option = struct
    let bind (f : 'a -> 'b option) : 'a option -> 'b option = function None -> None | Some x -> f x
    let map (f : 'a -> 'b) : 'a option -> 'b option = function None -> None | Some x -> Some (f x)
end

module Stream = struct
    include Stream
    
    let map (f : 'a -> 'b) (strm : 'a Stream.t) : 'b Stream.t =
        Stream.from (fun _ ->
            let x : 'a option =
                try Some (Stream.next strm)
                with Stream.Failure -> None
            in
            Option.map f x)
    let filter (f : 'a -> bool) (strm : 'a Stream.t) : 'a Stream.t =
        let rec aux () =
            try
                let x = Stream.next strm in
                if f x then Some x else aux ()
            with Stream.Failure -> None
        in
        Stream.from (fun _ -> aux ())
    let take (n : int) (strm : 'a Stream.t) : 'a Stream.t =
        Stream.from (fun x ->
            if x >= n then None else
            try Some (Stream.next strm) with Stream.Failure -> None)
end

let (%>) f g x = g (f x)

let () =
    let is_even n = n mod 2 = 0 in
    let double = ( * ) 2 in
    Stream.from (fun n -> Some n)
    |> Stream.filter is_even
    |> Stream.take 5
    |> Stream.map (double %> string_of_int)
    |> Stream.iter print_endline

I concern about 'a Stream.t is mutable.