My parents like foisting various self-help books on me, and while I sometimes groan to myself about it, I do read (or at least skim) them and extract useful bits of information out of them. This particular title quote is from Robert Kiyosaki’s “rich dad” in Rich Dad, Poor Dad.
“Intelligence is the ability to make finer distinctions” really spoke to me. I’ve since found it to be an extremely effective litmus test to determine if I’ve really understood something. A recent example comes from my concurrent systems class, where there are many extremely similar methods of mutual exclusion: mutexes, semaphores, critical regions, monitors, synchronized region, active objects, etc. True knowledge entails an understanding of the conceptual details differentiating these gadgets. What are the semantics of a signal on a condition variable with no waiting threads? Monitors and synchronized regions will silently ignore the signal, thus requiring an atomic release-and-wait, whereas a semaphore will pass it on to the next wait. Subtle.
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…because I don’t live in a room numbered 245s anymore. Yep. :-)
This is a cow. They munch grass next to the River Cam.
Pop quiz. What do matrix-chain multiplication, longest common subsequence, construction of optimal binary search trees, bitonic euclidean traveling-salesman, edit distance and the Viterbi algorithm have in common?
I’ve started formally learning OCaml (I’ve been reading ML since Okasaki, but I’ve never written any of it), and here are some notes about differences from Haskell from Jason Hickey’s Introduction to Objective Caml. The two most notable differences are that OCaml is impure and strict.
Features. Here are some features OCaml has that Haskell does not:
- OCaml has named parameters (
~x:i binds to i the value of named parameter x, ~x is a shorthand for ~x:x). - OCaml has optional parameters (
?(x:i = default) binds i to an optional named parameter x with default default). - OCaml has open union types (
[> 'Integer of int | 'Real of float] where the type holds the implementation; you can assign it to a type with type 'a number = [> 'Integer of int | 'Real of float] as a). Anonymous closed unions are also allowed ([< 'Integer of int | 'Real of float]). - OCaml has mutable records (preface record field in definition with
mutable, and then use the <- operator to assign values). - OCaml has a module system (only briefly mentioned today).
- OCaml has native objects (not covered in this post).
Syntax. Omission means the relevant language feature works the same way (for example, let f x y = x + y is the same)
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I am a member of a group called the Assassins’ Guild. No, we don’t kill people, and no, we don’t play the game Assassin. Instead, we write and run competitive live action role-playing games: you get some game rules describing the universe, a character sheet with goals, abilities and limitations, and we set you loose for anywhere from four hours to ten days. In this context, I’d like to describe a situation where applying the rule Don’t Repeat Yourself can be harmful.
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In which the author muses that “semi-formal methods” (that is, non computer-assisted proof writing) should take a more active role in allowing software engineers to communicate with one another.
C++0x has a lot of new, whiz-bang features in it, one of which is the atomic operations library. This library has advanced features that enable compiler writers and concurrency library authors to take advantage of a relaxed memory model, resulting in blazingly fast concurrent code.
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I’ve been having some vicious fun over the weekend hacking up a little tool called MMR Hammer in Haskell. I won’t bore you with the vagaries of multimaster replication with Fedora Directory Server; instead, I want to talk about rapidly prototyping scripts in Haskell—programs that are characterized by a low amount of computation and a high amount of IO. Using this script as a case study, I’ll describe how I approached the problem, what was easy to do and what took a little more coaxing. In particular, my main arguments are:
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This post is for those of you have always wondered why we have a forall keyword in Haskell but no exists keyword. Most of the existing tutorials on the web take a very operational viewpoint to what an existential type is, and show that placing the forall in the “right place” results in the correct behavior. I’m going to take a different approach and use the Curry-Howard isomorphism to explain the translation. Some of the logic examples are shamelessly stolen from Aaron Coble’s Logic and Proof lecture notes.
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Unattributed to protect the innocent. (But you can probably guess.)
“And so these poor programmers, they had to drink this much whiskey to get the job done.” [triumphantly produces a bottle of whiskey and places it on the table.] “And this group of programmers did X, and how hard was that? Two bottles of whiskey.” [places two more bottles of whiskey on the table] “But that wasn’t fast enough. And so this group of programmers did Y. Four bottles of whiskey.” [four more bottles appear] “As you can see, this is requiring an exponentially increasing amount of whiskey.”
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A complaint I once heard about SIPB is that it leans too much towards the system administration side: we proudly display the services we have deployed and neglect to talk very much about actually programming or conducting novel computer science research (despite the fact that we are very much programmers and some of us are quite research oriented.) So if you’re really not at all interested in that sort of thing (like me) you might think to yourself, “That’s very nice” and go and do something else.
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I recently sent Greg Weber an email about his xss-sanitize package, cautioning about his reuse of the pandoc sanitization algorithm for his own package. He responded (with good justification) that a mere caution was not very constructive! So here is my response, the “HTML purification manifesto,” which HTML Purifier follows and which I think is a prerequisite for any industrial grade HTML sanitization library. I will admit it’s a tough manifesto to follow, and I’ll talk about when you can get away with not following it to the line.
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