| If that was your intention, simply saying "I didn't find this talk useful" would suffice. It's not necessary to say that "Rich Hickey doesn't understand type theory". I would say that "X doesn't understand type theory" is becoming a common form of "middlebrow dismissal" [1], which is discouraged on HN. And that's exactly the scenario you described in proto3 - now every field could be encoded as a Maybe. No, in protobufs, the presence of fields is checked at runtime, not compile time. So it's closer to a Clojure map (where every field is optional) than a Haskell Maybe. This is true even though Google is using statically typed languages (C++ and Java). It would be true even if Google were using OCaml or Haskell, because you can't recompile and deploy every binary in your service at once (think dozens or even hundreds of different server binaries/batch jobs, some of which haven't been redeployed in 6-18 months.) This is an extreme case of what Hickey is talking about, but it demonstrates its truth. I don't find any relationship between types and anything I understand as "runtime behavior". Look up the concept of "type erasure", which occurs in many languages, including Haskell as I understand it. Or to be more concrete, compare how C++ does downcasting with how Java does it. Or look at how Java implements generics / parameterized types. [1] http://www.byrnehobart.com/blog/why-are-middlebrow-dismissal... |