Reason's type system is quite full-featured and has been refined over the last couple of decades. What we've seen so far is only an introduction to Reason's type system. In my opinion, you should become familiar with the basics before continuing to more advanced type system features. It's hard to appreciate things such as type safety without having experienced bugs that a sound type system would have prevented. It's hard to appreciate advanced type system features without getting slightly frustrated with what you've learned so far in this book. It's beyond the scope of this book to discuss advanced type system features in too much detail, but I want to make sure that those of you who are evaluating Reason as an option know that there's much more to its type system.
In addition to phantom types and polymorphic...