[seagreen]

You're making some good points here. Neither category theory informed typeclasses nor laziness are required for pure functional programming (henceforth PFP). Up until recently Haskell was the only PFP language in common use, so all those things got conflated in a lot of people's minds. Now we have PureScript (which doesn't have laziness) and Elm (which doesn't have laziness or typeclasses).

That said, you really should listen to @willtim about the `IO` type. Purity really is a big deal, and `IO` doesn't break it at all.