For me at least, I realized that a lot of what I liked about static typing was, one way or another, pattern matching. When you match on type, all of a sudden it's explicit in the code what you're working with. It doesn't capture anywhere near 100% of the value of static typing, but in effect you do wind up with functions which dispatch once and component functions in the interior that don't need to worry about getting passed something nutty. So the library boundary will take lots of logically equivalent inputs, but the output will pretty much always be regular.