CoditCompany

[<Property>]
let ``PositiveInt don't gets created if value is negative`` () =
    Arb.generate<int>
    |> Gen.filter ((>) 0)
    |> Arb.fromGen
    |> Prop.forAll <| fun x -> 
        None = posInt x

[<Property>]
let ``PositiveInt gets created if value isn't negative`` (FsCheck.PositiveInt x) = 

CoditCompany

public class ISBN13
{
  public ISBN13(string value)
  {
    ValidateStringNullOrEmpty(value);
    ValidateStringLength(value, 13);
    ValidateStringMatches(value, "[0-9]{9}");
    ValidateISBNCheckSum(value);
  }

CoditCompany

type ISBN13 = private ISBN13 of string

let ifTrueThen x = function 
    | true -> Some x 
    | false -> None

let (|NullOrEmpty|_|) = 
    String.IsNullOrEmpty 
    >> ifTrueThen NullOrEmpty

CoditCompany

type Book = 
  { ISBN13 : string
    Author : String50
    Pages : PositiveInt }

CoditCompany

public class String50
{
    public String50(string value)
    {
        if (string.IsNullOrEmpty(value))
        {
            throw new ArgumentException(nameof(value));
        }
        
        if (value.Length > 50)

CoditCompany

type String50 = private String50 of string

let ifTrueThen succ = function
    | true -> Some succ
    | false -> None

let (|NullOrEmpty|_|) = 
    String.IsNullOrEmpty 
    >> ifTrueThen NullOrEmpty

CoditCompany

type Book = 
  { ISBN13 : string
    Author : string
    Pages : PositiveInt }

CoditCompany

let (|Negative|_|) x = if x < 0 then Some Negative else None

let posInt x = function
    | Negative -> None
    | x -> Some <| PositiveInt x

CoditCompany

type PositiveInt = private PositiveInt of int

let posInt x = function
    | x when x < 0 -> None
    | x -> Some <| PositiveInt x

CoditCompany

type Book =
  { ISBN13 : string
    Author : string
    Pages : int }