It's more or less the haskell version of a struct or a public class with fields and no methods, except that you can specify more than one shape for the same typ

It's more or less the haskell version of a struct or a public class with fields and no methods, except that you can specify more than one shape for the same type. data MyMaybe a = Just a | Nothing ...means in Java speak "MyMaybe<a> is an abstract generic superclass with a final singleton subclass Nothing<a> having no fields, and a final subclass Just<a> having one field of type a" You then write functions that take that data and use it.