In my experience, this is not the case. In my current project, I am parsing and analyzing a dialect of SQL. As you say, "we must develop systems with incomple

In my experience, this is not the case. In my current project, I am parsing and analyzing a dialect of SQL. As you say, "we must develop systems with incomplete knowledge". Had it been necessary that I get my rules right up front, there would be tremendous pain - the documentation is inconsistent, incomplete, and incorrect. Tremendous agreement there. This is no case for foregoing types. In order to write code we must be defining expectations of how our system works. Even ideally loosely coupled, code depends on the behavior of other code. When we learn that a given interface is no longer going to work, we need to find and change everywhere that relied on that interface. Working in Haskell I was able to sketch out a preliminary and incomplete set of rules; as I found them not to work I could change them - with tremendous assistance in finding exactly the points that needed to change in tandem. Working in Python earlier this year, much smaller changes to much simpler code has been substantially more painful.