Types are like the Weather, Type Systems are like Weathermen - Matthias Felleisen

Matthias Felleisen, one of the developers of Racket, recently gave a talk about the motivation behind typed Racket; it can be found here: [VIDEO]

One thing that was a personal shocker for me to hear, from not just anyone, but Matthias Felleisen himself - "My research group has investigated the topic for almost 3 decades, and we came to the conclusion that Hindley-Millner doesn't really work". I was really baffled. That was at ClojureWest 2016. Here's the talk itself [VIDEO] . That talk is not about Clojure - Felleisen doesn't even use Clojure. That happened before Clojure.spec was announced. I couldn't really figure out what exactly he was talking about. Not until later, when I tried Spec.

how is static typing lacking evidence? don't we use that in rust to prevent the existence of large swaths of errors vs say C? i know for sure when turning on typescript for some javascript projects at work we found many issues, those all seem like wins? Why when I look at some dynamic languages say for example clojure i see stuff like type annotations in their core libraries, and then spec's to help provide a lot of what a type system can do? do you have maybe a counter argument to this fellow [VIDEO]