Posts (page 2)

Monads In The π-Calculus

Mar 9, 2009
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While I was in the shower this morning, it occurred to me that I should make a note for myself about how monads work in the polyadic D-fusion calculus.

The type construction is simply a channel (να) for sending a value of the underlying type.
The unit function is a channel (να λ(λ(να))) for sending a value of the underlying type and receiving a responsive channel that carries the resulting monadic value.
The binding operation is a channel (να ν(να λ(λ(νβ)))) λ(λ(νβ))) for sending two values, 1) a monadic value of type α and 2) a channel for sending a value of the underlying type α and receiving a responsive channel that carries the resulting value of monadic type β; the binding operation channel also permits receiving a responsive channel that carries the resulting value of monadic type β.

Easy as cake.

Note: the process defined according to the type above for the binding operation always starts when both inputs are available. There are two possible optimizations here: one where the process begins immediately when the value of monadic type α becomes available and one that begins immediately when the bound channel becomes available. The description of these types is left as an exercise.

Update: I made some consistency errors in the first revision of this post, so I went back and edited it to correct errors.

Curried Actions In The Polyadic π-Calculus

Feb 28, 2009
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When you're building a concurrent functional programming language around an internal language derived from the π-calculus, it's a known strategy [c.f. Pict, by Pierce and Turner] to allow applicative expressions to be used in the place of π-names in action prefixes. These are a kind of syntactic sugar that expand to a concurrent process that produces the result of function application on an ephemerally bound name that takes the place of the expression.

I've been thinking lately about how currying might work in this syntax. It's doable, but I'm not sure it can be done implicitly the way OCaml and Haskell do it, i.e. where it always makes sense for the programmer to use the curried syntax over the uncurried syntax, because A) it's more flexible and B) it's faster (the uncurried form involves more boxing).

In OCaml, you can define a function like this:

let f u : int -> int -> int =

printf "u=%u\n" u;

fun v -> u + v

When you call that function with a partial application of only one argument, as in let x : int -> int = f 5 in ..., the printf function is called and the result is a function object that adds 5 to its integer argument and returns the result without printing any further output.

I'm not sure how OCaml does this, but it does.

What I want is a similar thing in the D-fusion calculus [a derivative of the π-calculus I've mentioned previously]. I think it might be doable, but I haven't figured it out yet. It seems like the arrow type operator actually needs to be a constructor in the derived syntax. The core internal syntax needs to allow for various principle channel sorts to appear in the derived syntax as expressions involving the arrow operator.

In other words, consider this derived type expression for a binary function in two polymorphic types:

∀α β. α → β → α

It can be derived from two different internal language principle type expressions that can be used equivalently in functional expressions so long as the compiler keeps track of things properly:

A :: ⟦ ∀α β. να νβ λ⟦ λα ⟧⟧

B :: ⟦ ∀α. να λ⟦ ∀β. νβ λ⟦ λα ⟧⟧⟧

The type expression in A) means send two names, one of type α and the other of type β, and receive one name of type ⟦ λα ⟧ where the response will arrive. The type expression in B) means send one name of type α and receive a name of type ⟦ ∀β. νβ λ⟦ λα ⟧⟧ where to send another name of type β and receive a name where the response will arrive. A functional definition where B and A are not equivalent processes would need to be recorded in the compiled module in pretty much the same way that OCaml does its magic.

I need to figure out how to handle that. I think, but I'm not sure, that this is what goes on inside compile interface files in OCaml. The signature says 'a b. 'a -> 'b -> 'a, but the .cmi file says the moral equivalent of "here is the address for partial applications in one variable, and here is another address for full applications in both variables."

More Math Noodling

Feb 26, 2009
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Last night, I think I figured out some important things about the π-calculus.

p1. I believe there is a monadic D-fusion calculus in which it is possible to elaborate the canonical polyadic version described in the paper by Boreale, Buscemi and Montanari. (I don't think this is particularly surprising.)

p2. I believe I can elaborate the monadic D-fusion calculus with Milner's π-calculus. (It's possible, though it seems unlikely, that this is a novel observation. Of course, it's also possible that I'm wrong, and I don't really understand the D-fusion calculus.)

p3. I suspect— though, I can't say I'm very confident— that I will soon have a sorted derivative of the polyadic D-fusion calculus (at least, the D-fusion calculus as I understand it) in which I may be able to elaborate ML^F as described in the paper by Botlan and Rémy. [This, I believe, would be a noteworthy achievement.]

Naturally, because I am just a simple-minded code-monkey and not a real mathematician, I'm pretty much incapable of publishing results in the conventional manner with any hope of them surviving peer review. Maybe, if I get some spare time today, I'll buy a download of MathType and start trying to write up my thoughts in something approaching the conventional format for such things. What's the worst that can happen? (Answer: I'll be branded as a kook.)

Update: Ah, I see where I went wrong in p2 now. I forgot how the D-fusion calculus really is strictly more expressive than Milner's π-calculus because the scope of λ-bound variables can be weakened via the λ- OP E N rules. Okay, now I'm back on track.

"You Suck As A Writer, George." Part I

Feb 23, 2009
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I've now had occasion to watch the first two-thirds of Star Wars: The Phantom Menace with my three-year-old son about five times. (He can't quite sit through the whole thing before he wants to wobble off to do something else, which on the whole I chalk up to him being three. He can't sit all the way through any film that long. It's just not something a three-year-old like him is going to do.) It's interesting watching what holds his attention. I've learned a few things about story from keeping an eye on him while he watches movies. It's especially interesting watching Star Wars: Episode I with him.

I should remind my friends that I do not share the commonly received wisdom that the Star Wars prequels represent a terrible crime against a beloved franchise from our generation's collective childhood. It's my considered opinion that the first three films were every bit as mockworthy and cheesepacked as the later prequels, larded with bad writing and horrible acting. Taken as a whole, the entire six film sequence from start to finish makes a pretty consistent bit of pulp science fantasy. It's not Masterpiece Theater people, it's freaking Star Wars. Get a goddamn grip.

However, watching Episode I with my son, it's interesting to note what catches his attention and makes him ask me questions about what's going on with the characters. He likes the whole action sequence aboard the Trade Federation ship that opens the film, and he wants to know who are all the players (even the background extras) and what they're doing. He doesn't have the bad reaction to Jar Jar that all of You People suffer, and his attention stays focused all the way through the whole sequence in Gunga City, the rescue of Queen Amidala and the escape from Naboo.

The sequence where the boy loses all interest? Everything on Tatooine leading up to the pod race. He loves the pod race, of course, so I've now watched that chapter about fifteen times. There's a lot going on in there that you miss the first time through! Sadly, once the pod race is over, he loses interest again.

The fight with Darth Maul just before they leave for Coruscant is, interestingly, too short. It doesn't set him up sufficiently as a bad guy in the piece. In fact, if I were to rewrite Episode I, then I'd definitely go back and give Darth Maul all of Sidious's lines in the opening sequence. I'd also have him lurking around on Naboo in person. Dude should have been hanging all over the heroes like a dark cloud from Page Fricking One. When we get to the line where the Viceroy's lackey says, "This is getting out of hand. Now there are two of them," I would have made that where we first get to see Sidious.

At some point, I'm going to start the movie for the boy right at the pod race chapter and let him watch all the way to the end (minus the gruesome parts that will give him nightmares). It'll be interesting to see what other major failurages Mr. Lucas made that my three-year-old will helpfully sort out from all the other stuff everyone complains about. I mean, I've been complaining about a lot of what goes slow on Tatooine in Episode I, but I didn't quite get what was the most glaring flaw until I started watching my son react to it. Darth Maul shows up, and he's confused. You could fix an awful lot of what went wrong in Episode I just by introducing Darth Maul a lot sooner.

"Nar, Hippies!"

Feb 20, 2009
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Richard K. Morgan slags on Tolkein in a pretty good essay here.

“I tell you, it’s no game serving down in the city”

- Gorbag - forgotten orc captain from Minas Morgul

[...]

That little twist of urban angst quoted above is one such trace. It comes at the end of The Two Towers and is part of an on-going set of dialogues between two orc captains at the tower of Cirith Ungol. And for a while - until Tolkien remembers these are Bad Guys and sends the wearyingly Good and Wholesome Sam up against them - we get a fascinating insight into life for the rank and file in Mordor. [...]

Go read the rest of it. He's pointing out what, for me, is one of the little joys of reading The Lord of the Rings, the stories of the little guys who aren't destined to be king of the world, who have their own motivations that keep them plodding forward so that somebody else can get all the glory when the battles are over. Like Morgan, I wish there more of that and less of the incessant elvish singing, but Tolkein is an acquired taste. I get that.

Morgan continues.

[...]

The great shame is, of course, that Tolkien was not able (or inclined) to mine this vein of experience for what it was really worth - in fact he seemed to be in full, panic-stricken flight from it. [...]

I'm a bit more forgiving of Tolkein than Morgan admits, on the grounds that I'm sympathetic to writers who suffer from what we now lovingly call Post-traumatic Stress Disorder. (Tolkein probably would have called it Shell Shock, I'm guessing.) Here's Morgan walking himself back a bit:

[...] I suppose it's partially understandable - the generation who fought in the First World War got to watch every archetypal idea they had about Good and Evil collapse in reeking bloody ruin around them. It takes a lot of strength to endure something like that and survive, and then to re-draw your understanding of things to fit the uncomfortable reality you've seen. Far easier to retreat into simplistic nostalgia for the faded or forgotten values you used to believe in. [...]

Yeah. I'm okay with Tolkein not wanting to go there. The man earned a nice, quiet retirement by writing those books, so I'm completely fine with him leaving to posterity the process of figuring out how Good and Evil work in a world where nation-states resolve conflicts by turning their entire societies into industrial corpse manufacturing systems.

That said, I did note this: Mr. Morgan has apparently written a fantasy novel. I suppose I should read it.

I'm Outraged By President Obama

Feb 10, 2009
2 comments

Glennzilla explains in his trademarked, exhaustively linked way what happened.

Basically, Mr. Obama campaigned on a promise to stop the abuse of the executive state secrets privilege initiated by President George W. Bush, and now we discover that he has broken this promise.

It's a big deal.

The abuse of the state secrets privilege that President Obama is now continuing is preventing the federal courts from hearing cases against the U.S. government that involve the illegal and morally bankrupt "extraordinary rendition" program that kidnapped people without warrant or due process and delivered them foreign countries where the reasonable expectation is that they would be tortured.

It's outrageous. No, I'm not surprised that President Obama has done this, but I'm no less outraged by it. If you're surprised, then consider this your wakeup call. The game was not over in November when you voted out the jackholes; now, you gotta MAKE them live up to their promises. It's time to start rotating and radiating again, people. President Obama needs to understand that he's going to have to walk back on this or there will be hell to pay. Start wailing in your senators. They're the people who can make him sweat over this. Do it now.

There is nothing more important for citizens than putting a stop to the U.S. torture state.

The New Faith Of The True Emperor

Feb 2, 2009
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A while ago, I participated in a lexicon game run by a friend called The New Faith of the True Emperor. The result is at least a novel's worth of SF/F fiction content collaboratively competitively developed by a team of around twelve people. In this case, the theme is far-future dark science fiction weirdness.

It was great fun playing the game, even though real life intervened and made it tough for all of us to complete it. I had to drop out and wasn't able to return for the wind-up. Still, the resulting fiction product is interesting for its novelty. Like all lexicon games, the thing that separates the content from the more collaborative approach of building alternate world fiction is that the discontinuities aren't errors; they're a critical part of the content.

Anyway, this is a short message to promote the release of the material to the public. It has a non-commercial share-alike Creative Commons license, so it's completely free fiction. Enjoy!

Attention: Near-future Science Fiction Writers!

Jan 30, 2009
2 comments

When you next sit down to start extrapolating current trends in information technology and communications engineering for the purpose of envisioning what might be possible in the foreseeable future, would it kill you to find an actual information and communications engineering specialist who knows something about what are the insurmountable problems due to the laws of physics, and to buy that guy— sadly, it's almost always a guy— buy that guy a beer and ask him whether your cool whizzy SFnal idea on which you hope to hang your whole story is even remotely scientifically plausible?

Example: I have completely lost my patience with @FAMOUS_AUTHORS who utterly fail to comprehend A) It's The Latency Stupid, B) More CPUs ≠ Faster Algorithm Execution, and C) Global Multicast is Insecure and Unmanageable. I can sort of understand not grasping one or two of these concepts, but all three of them? Come on. Guys, you're not even trying, are you?

Without naming the guilty whose books I've read recently, let me just say that I'm particularly tired of the SFnal tropes that involve either A) unmanaged, zero-configuration, anarcho-utopian wide-area Wi-Fi mesh networks with the latency, bandwidth and error characteristics of highly redundant, subterranean fiber optic networks linked by big iron switches in hardened central offices; or B) emergent, sapient personalities hosted by digital processing functions embedded in a vast distributed global internet of small, commodity, even disposable devices.

I mean, at least when the previous generation decided to hand-wave over the small problem of how faster-than-light travel/communication is supposed to be possible, they were pretty open about it. They would at least go to the trouble of making up some bullshit technobabble about how some future scientist would get the credit for discovering the super-double-secret SF/F magick that allowed such stuff to happen despite our best current understanding of physics saying otherwise. Is that so goddamn difficult for you to do, too?

Seriously. I know you guys are hella freaking smart— much smarter than me. I know this because I hear it all the goddamn time. So why do I want to slap you for pretending to be stupid when I read your books? Why!?

I Don't Know What This Says About Me

Jan 13, 2009
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As I've been getting a better handle on my generalized anxiety disorder over time, I've found that I've needed to become more and more discriminating about my sources of news and opinion about current events, particularly in the area of politics and government affairs, if I want to lower my risk of experiencing further episodes of emotional dysregulation.

First, I had to cut out the neo-pentecostal religious fruitbats. That was like a schizophrenic deciding to stop dropping the brown acid. Now, I ration little bits of the Dark Christianity community on LJ and the TalkToAction website to myself, and it seems to keep the monsters tagged and bagged without me having to work up too much of a sweat in the process.

Second, I had to cut out the right-wing authoritarian talk radio; starting with Rush Limbaugh, and eventually with the whole AM/FM radio spectrum. Can't do it. I let the Media Matters people tell me what their latest brain damage is now. Yes, I still need to know, but I just can't bear facing it directly anymore without paying an unacceptable price for it.

Next, I had to shut off all the 24-hr cable news channels. No, not just the FauxNewsChannel. I had to ban them all. However, until recently, I had not found a good substitute for the kernels of useful information buried under all the steaming piles of horseshit they routinely purvey. For a long time, I'd get it from scouring a bunch of blogs in my "Moonbat" bookmark category, e.g. Digby, FiredogLake, etc., but these sources— while they don't trigger the anxiety so much— they do require more work to read than I want.

I have now found the ultimate replacement for the 24-hr cable news channels. I have been testing it for several weeks now, and it never fails to disappoint: the TalkingPointsMemo TPMtv channel, especially the Day In 100 Seconds episodes. I love them. They're like the little vomit flavored jelly beans in the Bertie Bott's Every Flavor Beans. They taste just enough like having somebody else's vomit in your mouth that you can pretend like it's the real thing, but hey— it's a jelly bean. How bad can it really be?

If you're one of those people who still watches the 24-hr cable news channels at times because you think they will help you figure out for yourself what the beltway insider village-of-the-damned consensus happens to be this particular political instant, and you're not willing to cede control of that analysis to some self-selected "media critic" yet, then I strongly encourage you to watch the TPMtv channel instead. You'll feel just as filthy, and you'll be every bit as well-informed, but it will only take 100 seconds a day. That's a huge win, if you ask me.

All Hail MightyGodKing

Jan 9, 2009
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Just click through to his post where he photoshops the covers of old, popular genre books to give them titles that more accurately describe their contents. My favorite: Mary Sue Gets A Dragon, by Anne McCaffrey.