Maybe.fs

open System

type Maybe<'a> =
    | Just of 'a
    | Nothing

let Unit (x: 'a) : Maybe<'a> =
    Just x

let Bind (f: 'a -> Maybe<'b>) (mx: Maybe<'a>) =
    match mx with
    | Just x -> f x
    | Nothing -> Nothing

let Example1 x =
    Unit(x)
    |> Bind (fun x -> Unit(x + 4))
    |> Bind (fun x -> Unit(x * 100))
    |> Bind (fun x -> if x >= 2400 then Unit(x) else Nothing)

let Example2 x =
    Unit(x)
    |> Bind (fun x -> if x = 0 then Nothing else Unit(x))
    |> Bind (fun x -> Unit(50 / x))

let PrintVal (x:Maybe<'a>) : unit =
    match x with
    | Just x -> Console.WriteLine(x.ToString())
    | Nothing -> Console.WriteLine("No value returned")

[<EntryPoint>]
let main argv = 
    20 |> Example1 |> PrintVal
    10 |> Example1 |> PrintVal

    0 |> Example2 |> PrintVal
    10 |> Example2 |> PrintVal

    0