ShortCode.fsx

type ShortCode = private ShortCode of string
type ProductShortCode = private ProductShortCode of ShortCode
type AccountShortCode = private AccountShortCode of ShortCode

module ShortCode =
    let create s = 
        if System.String.IsNullOrEmpty s then None
        elif s.Length > 15 then None
        else Some (ShortCode s)

    let value (ShortCode s) =
        s

module AccountShortCode =
    let create s = 
        match ShortCode.create s with 
        | Some sc -> Some (AccountShortCode sc)
        | None -> None

    let value (AccountShortCode (ShortCode s)) = s

module ProductShortCode = 
    let create s = 
        match ShortCode.create s with
        | Some sc -> Some (ProductShortCode sc)
        | None -> None

    let value (ProductShortCode (ShortCode s)) = s