The Right Types of Assumptions

A little while back I was discussing my Haskell and AI article with some other engineers I know. These people are very smart and come from diverse backgrounds of software engineering. But they tend to prefer dynamically typed languages like Javascript and Ruby. So they don’t buy into Haskell, which makes them no different from most of the engineering community.

Still, some things about the discussion surprised me. I heard, of course, the oft-repeated mantra that types do not replace tests. But even more surprising was one claim that types do not, and are not even meant to provide any kind of safety. One engineer even claimed he thinks of types only as directives to help a compiler optimize a program.

Now, it would be bold to claim that Haskell is better for all things and all circumstances. But I don’t think I’ve ever done that on this blog. It would also be unrealistic to claim that Haskell’s type system can replace all testing. And in fact I’ve dismissed that claim a couple times on this blog.

But surely Haskell’s type system gets us something. Surely, compiled types add some layer of extra safety and correctness to our programs. I’ve never thought this to be a particularly controversial point. Any yet many smart people dismiss even this claim. So these conversations got me thinking, why is it that I think Haskell's type system is useful? Why do I believe what I do?

Convincing Myself

For me, the evidence is a matter of personal experience. And a lot of other Haskellers would agree. I programmed in dynamic languages, such as Python and Javascript. I’ve also dealt a lot with Objective C and Java, which have static types but do not restrict effects as Haskell does.

It’s very clear to me where I get fewer bugs and write cleaner code that is more often correct, and that’s with Haskell. But of course I can’t base everything on my own experience, which could be subject to many biases. For instance, it could be that I haven’t spent enough time writing in dynamic languages at an industry level. It could also be that I happen to have become a more competent programmer in the last year. Perhaps I would have seen similar improvements no matter what language I focused on. Still, Haskell changed my programming in ways that other languages wouldn't have. I feel I could now go back to other languages and write better programs than I could before I learned Haskell.

Regardless, I would not feel as confident. Without Haskell's guarantees, there’s a great deal more mental overhead. You have to always ask yourself questions like, is every error condition checked? Are all my values non-null? Have I written enough tests to cover basic data format cases? Have I prevented effects like slow-running DB operations in performance critical places? Determining the answers to these might require a line-by-line audit of the code. Thorough code review is good. But when it becomes a pain, corners will get cut.

Perhaps if I had a couple more years experience writing Javascript, I wouldn’t view these tasks as such a burden. But one of the best answers I ever read on Quora gave this piece of advice. As you become a better programmer, you don’t get better at keeping things in your head and knowing the whole system. You get better at sectioning off the system in a way that you don’t have to keep it in your head. Haskell lends itself very well to this approach.

So it’s true that other languages can be written in a safe way. But Haskell forces you to write and think safely. In this regard, Haskell would actually be a fantastic first language.

Empirical Evidence?

Now there’s been some efforts to study the effects of programming language choice. This dissertation from UC Davis examined many open-source code bases to find what factors led to fewer bugs. The conclusion, was that strongly typed, functional languages fare better. A much older paper from Yale found that Haskell was a clear winner when it came to code clarity. (Python and Javascript weren’t covered in the study though).

Case closed right?

Well of course not. With the UC Davis paper, many possible issues prevent firm conclusions. After all, it only studied open source code and not industrial code. Confounding factors might well exist. Functional projects could just have fewer users. This could explain fewer bug reports. Also, code size dwarfed any effects of language choice. More code = more bugs.

But it’s hard to see how we could settle this question with an empirical study. No one has access to programmers with arbitrary levels of experience in a language. The Yale paper might have had the right idea. But it would need a larger scale to draw more solid conclusions.

What Other Evidence is out there?

So failing this kind of assessment, what is the best way to provide evidence in Haskell’s favor? It’s rather hard to look past testimony here. It would be great to see more publicity around stories like at Channable. Engineers there were able to use convert a small piece of infrastructure to Haskell. The result was a system that had fewer bugs that they could refactor with confidence.

Of course, testimony like this is still imperfect. There could be major survivorship bias. For every person who posts about Haskell solving their problems, there may be 5 who found it didn't help.

There’s also the fact of the world that many people don’t like change. You could provide all the evidence in the world in favor of a particular language. Some people will still choose to fall back on what they know. For people who have “tried and true” business models, this makes sense. Anything else seems risky.

So how do we Convince People?

I’ll repeat what I’ve noted a couple times in previous articles. Network effects are currently a huge drag on Haskell. The more Haskell developers who are out there, the easier it will be to convince companies to give it a try. Even if it is only on small projects, there will be more chances to see it succeed.

What is the best way to go about solving these network issues? For one, we need more marketing/Haskell evangelism. That said, there is still a sense that we need more educational material at all levels. Helping beginners get into the language is a great start. But there's definitely another hurdle to go from hobbyist to industry level.


Every once in awhile it’s important to take a step back and consider our assumptions. I definitely found it worthwhile to reexamine some of my beliefs about Haskell’s type system. It's helped me to remember why I think the way I do. There’s a good amount of evidence out there for Haskell’s utility and safety as a language. But the burden is on us as a community to collect those stories and put them out there more.

If you haven’t tried Haskell before, hopefully I’ve convinced you to be one of those people! Check out our Getting Started Checklist for some good resources in starting your Haskell education.

If you’ve dabbled a bit and want to make the next step up, we also have a few other resources for you! Check out of Stack mini-course, our Recursion Workbook or our Haskell Tensor Flow guide!