June 2015

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  • 1:58 PM

Ask me ten years ago, and I'd say a blog entry, once published, should remain that way. Oh wait, I actually did say that:

I try never to delete anything substantive. Attempting to un-say something by deleting it is really just a case of hiding the evidence. I'd much rather correct myself out in the open than pretend I was never wrong in the first place.

The reasons not to delete come down to:

  • Not wanting to break the web by 404-ing a page
  • Wanting to be honest about what you’ve said in public
  • Keeping a record of who you were at some moment in time.

The counter-arguments are:

  • The web was designed to break. And anyway, the stuff worth deleting is usually the stuff nobody’s linking to.
  • Just how long does a mea culpa have to stand before it becomes self-indulgent?
  • Unless you’re noteworthy and dead, or celebrity and alive, the audience for your years-old personal diaries is particularly limited.
  • Publishing on the web isn’t just something you do, and then have done. It’s an ongoing process. A website isn’t just a collection of pages, it’s a work that is both always complete, and always evolving. And every work can do with the occasional read-through with red pen in hand.

That last point is the most compelling one. I was publishing a website full of things that, however apt they were at the time to the audience they were published for, just aren’t worth reading today.

So to cut a long story short, last weekend I un-published about 700 of the previously 1800 posts on this blog; things that were no longer correct, things that were no longer relevant, things that were no longer interesting even as moments in time, and things that I no longer feel comfortable being associated with. I don't think anything that was removed will be particularly missed, and as a whole the blog is a better experience for readers without them.

The weirdest thing about deleting 700 blog posts is realising you had 1800 to start with. Although to be fair, 1750 of them were Cure lyrics drunk-posted to Livejournal.

Under the hood

It's a testament to the resilience of Moveable Type that in the eleven years since I first installed it to run this blog, I've upgraded it exactly twice. If I’d tried that with the competition, I doubt I’d have had nearly as smooth a ride.

Moveable Type got me through multiple front-page appearances on Digg, reddit, Hacker News and Daring Fireball without a hitch, or at least would have if I hadn't turned out to be woefully incompetent at configuring Apache for the simple task of serving static files.

But as they say, all good things must come to end. Preferably with Q showing up in a time travel episode.

I replaced Moveable Type with a couple of scripts that publish a static site from a git repo, fully aware that I’m doing this at least five years after it became trendy. The site should look mostly identical, except comments and trackbacks haven't been migrated. They’re in the repo, but I'm inclined to let them stay there.

Look, bad things happen to people in fiction just like bad things happen in real life. And at least the people in fiction aren't real so it didn't really happen to them.

I get that.

And you can have great entertainment where bad things happen to bad people, or bad things happen to good people, or bad things happen to indifferent people who just happened to be in the wrong place at the wrong time.

I get that too.

But at some point you find yourself sitting on a couch watching a drawn-out scene where a child is burned alive screaming over and over for her parents to save her, and you think “Why the fuck am I still watching this show?”

Bad things happen in real life. Bad things have happened throughout history. So what, I'm watching television. If I wanted to experience the reality of a brutal, lawless campaign for supremacy between tribal warlords, there are plenty of places in the world I could go to see that today. I wouldn't survive very long, but at least I'd get what I deserved for my attempt at misery tourism.

Bad things happen in good drama, too. But drama comes with a contract. The bad things are there because they are contributing to something greater. Something that can let you learn, or understand, or experience something you otherwise wouldn't have; leading you out the other side glad that you put yourself through the ordeal, albeit sometimes begrudgingly.

To refresh our memories, here's how George R. R. Martin explained the Red Wedding:

I killed Ned in the first book and it shocked a lot of people. I killed Ned because everybody thinks he's the hero and that, sure, he's going to get into trouble, but then he'll somehow get out of it. The next predictable thing is to think his eldest son is going to rise up and avenge his father. And everybody is going to expect that. So immediately [killing Robb] became the next thing I had to do.

There are increasingly flimsy justifications for the horrors of Game of Thrones. They motivate character A. Or they open up space for character B. But in the end it's obvious that it's really about providing the now-mandated quota of shock, and giving the writers some hipster cred for subverting fantasy tropes.

I did not enjoy watching Sansa Stark’s rape. I did not enjoy watching Shireen Baratheon burned at the stake.

If that's what you want to watch TV for, go for it. But I'm out.

Seen on Twitter:

Either and Promises/Futures are useful and I’ll use them next time they’re appropriate. But outside Haskell does their monad-ness matter?

All code below is written in some made-up Java-like syntax, and inevitably contains bugs/typos. I'm also saying "point/flatMap" instead of "pure/return/bind" because that's my audience. I also use "is a" with reckless abandon. Any correspondance with anything that either be programatically or mathematically useful is coincidental

What is a monad? A refresher.

A monad is something that implements "point" and "flatMap" correctly.

I just made a mathematician scream in pain, but bear with me on this one. Most definitions of monads in programming start with the stuff they can do—sequence computations, thread state through a purely functional program, allow functional IO. This is like explaining the Rubiks Cube by working backwards from how to solve one.

A monad is something that implements "point" and "flatMap" correctly.

So if this thing implements point and flatMap correctly, why do I care it's a monad?

Because "correctly" is defined by the monad laws.

  1. If you put something in a monad with point, that's what comes out in flatMap. point(a).flatMap(f) === f(a)
  2. If you pass flatMap a function that just points the same value into another monad instance, nothing happens. m.flatMap(a -> point(a)) === m
  3. You can compose multiple flatMaps into a single function without changing their behaviour. m.flatMap(f).flatMap(g) === m.flatMap(a -> f(a).flatMap(g))

If you don't understand these laws, you don't understand what flatMap does. If you understand these laws, you already understand what a monad is. Saying "Foo implements flatMap correctly" is the same as saying "Foo is a monad", except you're using eighteen extra characters to avoid the five that scare you.

Because being a monad gives you stuff for free.

If you have something with a working point and flatMap (i.e. a monad), then you know that at least one correct implementation of map() is map(f) = flatMap(a -> point(f(a)), because the monad laws don't allow that function to do anything else.

You also get join(), which flattens out nested monads: join(m) = m.flatMap(a -> a) will turn Some(Some(3)) into Some(3).

You get sequence(), which takes a list of monads of A, and returns you a monad of a list of A's: sequence(l) = l.foldRight(point(List()))((m, ml) -> m.flatMap(x -> ml.flatMap(y -> point(x :: y)))) will turn [Future(x), Future(y)] into Future([x, y]).

And so on.

Knowing that Either is a monad means knowing that all the tools that work on a monad will work on Either. And when you learn that Future is a monad too, all the things you learned that worked on Either because it's a monad, you'll know will work on Future too.

Because how do you know it implements flatMap correctly?

If something has a flatMap() but doesn't obey the monad laws, developers no longer get the assurance that any of the things you'd normally do with flatMap() (like the functions above) will work.

There are plenty of law-breaking implementations of flatMap out there, possibly because people shy away from the M-word. Calling things what they are (is a monad, isn't a monad) gives us a vocabulary to explain why one of these things is not like the other. If you're implementing a flatMap() or its equivalent, you'd better understand what it means to be a monad or you'll be lying to the consumers of your API.

But Monad is an opaque term of art!

So, kind of like "Scrum", "ORM" or "Thread"?

Or, for that matter, "Object"?

In summary:

As developers, we do a better job when we understand the abstractions we're working with, how they function, and how they can be reused in different contexts.

Think of the most obvious monads that have started showing up in every language1 over the last few years: List, Future, Option, Either. They feel similar, but what do they all have in common? Option and Either kind of do similar things, but not really. An Option is kind of like a zero-or-one element list, but not really. And even though Option and Either are kind of similar, and Option and List are kind of similar, that doesn't make Either and List similar in the same way at all! And a Future, well, er…

The thing they have in common is they're monads.

1 Well, most languages. After finding great branding success with Goroutines, Go's developers realised they had to do everything possible to block any proposed enhancement of the type system that would allow the introduction of "Gonads".