I introduced core.typed to Circle, and I was responsible for most of the early type annotations in the Circle codebase. Because of me, Circle was also the first large contributor to core.typed's kickstarter campaign.

Other commenters are speculating that this kind of tool needs to be built into the language, and planned ahead of time. IMO, this is completely wrong. core.typed fits surprisingly well into the language, and there are no fundamental reasons in Clojure or core.typed preventing it from working well.

I largely agree with the criticisms raised in the post, but it's worth pointing out that core.typed is developed by one guy, part-time while working on his phd. The problems are all related to maturity of the project, and bandwidth. core.typed's version number is currently 0.3.11, which gives you an idea of its state.

Ambrose has shown what is possible; I'm confident that with more help, core.typed can become an amazing tool for finding bugs in production code.