From the point of view of a solo developer maintaining a large app over many years: I would not want to deal with static type checking and I would not find it u

From the point of view of a solo developer maintaining a large app over many years: I would not want to deal with static type checking and I would not find it useful, except for simpler subsets of my code. I do use spec, and I've used other checking solutions before. I also use :pre/:post conditions a lot, as well as plenty of assertions. But in a large and complex application the errors I'm likely to run into are not as simple as a mismatched type. My most valuable checks and specs constrain multiple data fields. Thinking about stuff I run into, I would say that the majority of errors are due to optionality — where a key is optional in some contexts, but mandatory in others.