Now if you understand the type family GHC extension, all this will be easily understood. If not, basically the idea is that you can automatically transform Array of Structs into Structs of Array by defining that transformation using a data family instance that you write yourself. For common types like tuples, the library already defined polymorphic instances for you.
Of course this transformation isn't always desirable and you don't have to use this. If your code isn't performance sensitive I wouldn't even bother with unboxed vectors; I'd just use regular vectors.
