false でも true でもない何か

NeitherTrueNorFalse.cs

using System;
using System.Runtime.InteropServices;

class Program
{
    static void Main()
    {
        Write(false);
        Write(true);

        Write(Bool(0)); // false と一緒
        Write(Bool(1)); // true と一緒
        Write(Bool(2)); // false でも true でもない何か
    }

    private static bool Bool(byte value)
    {
        var union = new MyUnion();
        union.Byte = value;
        return union.Bool;
    }

    [StructLayout(LayoutKind.Explicit)]
    private struct MyUnion
    {
        [FieldOffset(0)]
        public bool Bool;

        [FieldOffset(0)]
        public byte Byte;
    }

    static void Write(bool x)
    {
        switch (x)
        {
            case true:
                Console.WriteLine("True");
                break;
            case false:
                Console.WriteLine("False");
                break;
            default:
                Console.WriteLine("Other ");
                break;
        }
    }
}

NeitherTrueNorFalse.fs

#nowarn "9"

open System.Runtime.InteropServices

[<StructLayout(LayoutKind.Explicit)>]
type MyUnion =
   struct
      [<FieldOffset(0)>]
      val mutable bool: bool
      [<FieldOffset(0)>]
      val mutable byte: byte
   end

let bool value =
    let mutable union = new MyUnion()
    union.byte <- value
    union.bool

let write = function
    | false -> printfn "%s" "False"
    | true  -> printfn "%s" "True"
    | _     -> printfn "%s" "Other"

[<EntryPoint>]
let main argv = 
    write true
    write false
    write (bool 0uy)
    write (bool 1uy)
    write (bool 2uy)
    0