alt Hacker News> it is simply more enjoyable to design the types in your program than to write unit tests.
I have tried both and I have no idea what you're talking about.
> Making yourself think about “for all x” rather than a concrete x forces your brain to consider deeply the properties of x being used.
The entire point of dynamic typing is that you can think about interfaces rather than concrete types, which entails deep consideration of the properties of the object (semantics of the provided interface).
That's not the entire point of dynamic typing, because all the interface stuff comes from statically typed languages. Some* dynamic languages borrowed it, but most use "implicit" interfaces - where the interface is whatever kind of works, I guess.