I'm familiar with type theory and (often) a proponent of dynamic typing.<p>It depends on what you're doing. If you're building cathedrals-- high-quality, performance-critical software that can never fail-- then static typing is a great tool, because it can do things that are very hard to do with unit testing, and you only pay the costs once in compilation. There are plenty of use cases in which I'd want to be using a statically typed language like OCaml (or, possibly, Rust).<p>If you're out in the bazaar-- say, building a web app that will have to contend with constant API changes and shifting needs, or building distributed systems designed to last decades without total failure (that may, like the Ship of Theseus, have all parts replaced) despite constant environmental change-- then dynamic typing often wins.<p>What I like about Clojure is that, being such a powerful language, you can get contracts and types and schemas but aren't bound to them. I like static typing in many ways, but Scala left me asking the question, any time someone insists that static typing is necessary: <i>which</i> static type system?