[sousousou]

I agree. Once you understand typechecker error messages a little bit, refactoring becomes very simple (and fun!).

1. change a core type or function 2. fix all the type errors 3. yay

This is wonderful. I think the tradeoff is that you start a new system, you have to delay running the code for a while. Until you have your core. (Fortunately there is undefined :: a for such uses.)