Functional programming

type Seq<'a> = Getter of (unit -> ('a * Seq<'a>) option)

let PrintSeq (seq: Seq<'a>) =
    let rec _step getter =
        match getter() with
        | None -> ()
        | Some(el, Getter(nextGetter)) ->
            printf "%A, " el
            _step nextGetter

    match seq with
    | Getter(f) -> _step f

let Map seq f =
    let rec _step getter () =
        match getter() with
        | None -> None
        | Some(el, Getter(nextGetter)) ->
            Some(f el, Getter(_step nextGetter))

    match seq with
    | Getter(g) -> Getter(_step g)

let Reduce seq f =
    let rec _step value getter =
        match getter() with
        | None -> value
        | Some(el, Getter(nextGetter)) ->
            _step (f value el) nextGetter

    match seq with
    | Getter(g) ->
        match g() with
        | None -> None
        | Some(el, Getter(getter)) -> Some(_step el getter)

// Sequences

let Range a b c : Seq<int> =
    let rec _getter x () =
        if x >= b then None
        else Some(x, Getter(_getter (x + c)))
    Getter(_getter a)

let rng = Range 1 5 1
let x = Reduce rng (+)

match x with
| Some(y) -> printfn "%d" y
| None -> printfn "neon"