Dragging Haskell Kicking and Screaming into the Century of the Fruitbat

Yesterday, the new Haskell CLC decided to remove (/=) from the Eq typeclass. As expected, the community has embraced this change with characteristic grace. The usual state of affairs is that people who like the changes are silent, while people who don’t are exceptionally vocal. The result: people working hard to improve things only ever get yelled at, and nobody says “hey, you’re doing a great job. Thank you!”

To the new Haskell CLC, with my deepest sincerity:

You’re doing a great job! Thank you.

Today I’d like to talk a little about the problems I see in the Haskell ecosystem. These are by no means insurmountable problems. They’re not even technical problems. They’re social problems, which suck, because those are the sort that are hard to solve.

The (/=) proposal has caused a surprising amount of uproar about such a stupid change. But why? Nobody actually cares technically about whether we can define not-equals instead of equals. I mean, I don’t care. You don’t care. I’m willing to bet dollars to donuts that nobody reading this essay has actually ever defined (/=) in an instance.

No, the outcry is because (/=) is a proxy for the real issue. As best I can tell, there are three camps, and everyone is talking past one another. This is my attempt to organize the camps, steel-man them (well, two out of three), and respond with my commentary.

Personally, I support the removal of (/=) because it’s a tiny, inconspicuous change that nobody is going to notice. It’s a bright beacon in the darkness of the ecosystem saying “hey, the situation sucks, but we’re willing to improve the situation.” Haskell has tons of problems like this, none of which are controversial — things like how head is antithetical to everything we like about Haskell, and yet it’s included by default in every fucking module of all time. Yes, there are valid arguments as to why it shouldn’t be removed, but nobody would argue to put it in if we were designing Prelude today.

In my eyes, removing (/=) from Eq shows that we as a community are willing to pay the cost to move out of a bad Nash equilibrium. Because as far as I see it, there are only two options:

1. break backwards compatibility and pay the migration costs
2. don’t break backwards compatibility, and pay the costs of having a shitty standard library forever

Asymptotically, option 1 is better than option 2. There is a constant amount of code today that we will need to fix, compared to a linear (or worse!) amount of work in the future to work around having a shitty standard library. And yes, that cost probably is forever, because if we have too much code to break today, we’re going to have even more code that will break tomorrow.

I want us to be able to remove (/=), because it gives me hope that one day we will be able to add Foldable1, and get join and liftA2 into Prelude, and the other hundreds of tiny improvements that would all of our lives better. Not profoundly, but each one saves us a few seconds, multiplied by the number of practitioners, integrated over all of our careers.

And yes, those things will come at a cost, but it’s a cost that is getting bigger the longer we don’t pay it.

In the particular example of (/=), there isn’t even any cost. There are ~50 packages that define (/=), and the solution is just to delete those definitions. Yes, it’s churn, but I personally am willing to send a patch to each package. If you’re the maintainer of such a package, email me and I’ll just go fix it for you.

This is not a big issue.

The second camp as best I can tell, are educators who aren’t particularly up to date on what Haskell is in 2021. These are the people saying “this will break our tutorials” (and, I suspect, are also the ones who say “we need head in Prelude because it’s good for beginners”.) While this group clearly has good intentions, I don’t think they get it. Educational materials for everything go obsolete, made much worse by the half-life of knowledge. If this is truly a thing you care about, just update your tutorials. There is no shortage of people in the community writing explanatory material, and I guarantee they will rush in to fill any void.

Of much more importance is third camp. They also seems to not care about (/=) in particular. But they are concerned about “backwards compatibility at all costs.” And to them, it seems, (/=) is a slippery slope. If we can’t maintain backwards compatibility for something as stupid as (/=), we’ve got no chance of having long-term maintainability. It’s a perfectly good argument.

To quote Dmitrii:

The size of breakage doesn’t matter. Breakage is breakage.

My personal rebuttal against this attitude is that it gets us stuck in extremely suboptimal equilibria. If we can never break anything, then every mistake must exist for perpetuity. By virtue of being human, we’re unfortunately fallible, and thus are going to make mistakes.

However, I can definitely sympathize here. If every week you are called on to fix a tiny, breaking change, sooner than later you’re going to quit. We should not encourage any behavior that leads to burnout in our best players. That’s a bad long term plan.

But in my experience, it’s not breaking changes that are the problem. It’s lots of breaking changes that are the problem. Breaking changes are annoying, sure, but what’s worse is the context shifting necessary to fix a breaking change. Doing the work is $O(n)$ with respect to the breakages, but there is an extremely high constant factor. With this in mind, one big breakage is significantly better than lots of tiny breakages.

Since we’re just about to break things, might I again suggest we add Foldable1, and clean up Prelude? If breakage is breakage (it is), we might as well take advantage of it and do as much cleanup as possible. This is an excellent opportunity. The status-quo is for all of us to argue about it every week, with half the people saying “these are bad circumstances and we should fix them,” with the other half saying “yes, they are bad circumstances, but breakage is worse.”

But given that we now have breakage, let’s make the most of it.