Immutability and types go hand in hand. Why? Well with immutability you can do more modelling of your domain as data and then the type system helps you manipula

Immutability and types go hand in hand. Why? Well with immutability you can do more modelling of your domain as data and then the type system helps you manipulate this data only in valid ways. No type system (I am aware of) can model and check mutable domain models.