Option monad

gistfile1.txt

type OptionBuilder() =
    member this.Return x = Some x
    member this.Bind(x, f) =
        match x with
        | Some x -> f x
        | None -> None
    member this.ReturnFrom x = x

let option = OptionBuilder()

let test =
    option {
        let! x = Some 3
        let! y = Some 4
        return x + y
    }

let test2 =
    option {
        return! Some 6
    }

let test3 =
    option {
        let! a = test
        let! b = test2
        return a * b
    }

let test4 =
    option {
        let! q = None
        let! t = test3
        return q * t
    }