[matt-noonan]

In Haskell designs, developers tend to be quite careful about setting things up so that verifying types does indicate valid data. Coming from other languages (C++, Common Lisp, and Python in my case), it can be a little surprising just how often and how easily you can make this happen.

[akmiller]

You can do similar things with spec for Clojure. As I stated in another response that is opt-in obviously so it requires more discipline perhaps but it is definitely available.

[willtim]

Null checks are also opt-in, that's why Tony Hoare calls null his "Billion Dollar Mistake". Explicit runtime checks are in no way "similar" to static typing! Static typing is a machine-checked proof of correctness for a certain class of properties.

[matt-noonan]

I'd rather have the compiler ensure that my discipline (and my team's) never slips, and to get guarantees about all possible executions instead of just those executions that have been tested.

For these reasons and others, I don't personally find run-time checks to be an adequate replacement for compile-time checks. But there is no really convincing research on the subject, and I certainly don't begrudge your preference here.