Helps clearify things for this blog post: http://blog.bjartwolf.com/?p=4522

Person.cs

public class Person
{
    private readonly PersonState _state;

    public Person(string name)
    {
        _state = new PersonState(name);
    }

    public string GetName()
    {
        return _state.Name;
    }

    public void ChangeName(string name)
    {
        _state.Name = name;
    }

    private class PersonState
    {
        public string Name { get; set; }

        internal PersonState(string name)
        {
            Name = name;
        }
    }
}

public class SomeThing
{
    public SomeThing()
    {
        var x = new Person("Tomas");
        x.ChangeName("John");
        x.GetName();
    }
}

Person.fs

module Person = 
    type PersonState = private {name: string}
    let create name = {name = name}
    let getName state = state.name
    let changeName name state = {state with name = name}

module Something = 
    open Person
    let x = create "Tomas"
    let y = x |> changeName "John"
    let name = x |> getName