To be fair, this article is really pretty "cutting edge" as far as Haskell goes. It describing a new feature they're planning on adding to the Haskell compiler,

To be fair, this article is really pretty "cutting edge" as far as Haskell goes. It describing a new feature they're planning on adding to the Haskell compiler, one that significantly extends the type system in an interesting way. I think it's fair for them to assume comfort and familiarity with Haskell syntax and code when writing this article; their audience is folks who are likely to know about and use somewhat esoteric GHC extensions...