[tmhedberg]

I'm aware of dependent types and, more generally, the strong undercurrent of emphasis on provable correctness in the Haskell community at large. I don't disagree at all with what you wrote, but it's not what I was referring to with my comment.

My disagreement was specifically with the implied claim that it can be mathematically proven that Haskell code is easier to maintain than code written in other languages. That has indeed been my experience with Haskell, but I do not think it is directly provable. What seems easy for me may be stupefyingly difficult or confusing for someone else.

"How easy something is" is not really a quantifiable measurement; it is a subjective experience. As chongli points out, however, there are related measurements that can be taken, such as cyclomatic complexity, and those at least seem to be correlated with ease of maintenance. So perhaps I'm just being overly pedantic!

[jroesch]

I misread your comment, usually people challenge that point. I totally agree that it is difficult to talk about maintainability in an objective fashion, but there is something to be said about having as many of your assumptions in your codebase vs. your test suite. My experiences working in a Ruby code base is that many assumptions have been encoded in the tests, and not notated in the main code base. When those assumptions change there is a large burden on the programmer of having to unify ad-hoc assumptions from both the test cases and main code base. Validating whether those assumptions still hold, or if it is a test from 3 years ago, and has only been vacuously passing.

I found working in a big Ruby code base that this required spending a non trivial amount of time unifying the two. In that regard by minimizing the amount of test code one has to write and maintain I would argue that maintainability goes up. I've also seen a lot of FP practitioners boasting about relatively low test to code ratios, while in the Ruby world often times you have at least 2x test code, since often times you even have to validate assumptions like `object.responds_to? :foo`.