I know, I know. We've been having some interesting discussions about Clojure, Haskell and dynamic and static typing on these stories

https://news.ycombinator.com/item?id=15602658

https://news.ycombinator.com/item?id=15593069

My comment was intended to be a wry one referencing those very interesting discussions and hinting that if you have types then you can more easily make breaking changes internally that aren't visible externally.

Dubious. The maintenance argument is weak. https://www.youtube.com/watch?v=2V1FtfBDsLU&feature=youtu.be...

I'm not sure what you mean. I thought it was self-evident that if your interface is an abstract type then you can change the implementation without breaking consumers. If you don't think it's true then please can you explain how? I thought the Clojure argument is not that types don't provide beneficial encapsulation, but that it's not worth paying the cost for them. Again if you know any different I'd be pleased to hear.

Apples and Oranges. We're talking about changing the interface. Did you watch the video segment?

> We're talking about changing the interface.

Who's "we"? I'm talking about changing the implementation.

> Did you watch the video segment?

I watched the bit where he said if you add a constructor to a sum type you have to change everywhere it's pattern matched. True. I'd love to see Clojure's solution where you don't have to change any existing code!

EDIT: Oh wait, I think it's even worse than that. I think he's talking about product types. In which case you should use projection functions and indeed you need to make no changes to old code!