Life-critical wording

I try to impress upon my students the importance of clear expression. Today's news contains an example where choice of the right word may be life-critical.

The experts reworded phrases that people found confusing, and then retested them in several sittings, including one-to-one interviews.

Prof Raynor said "avoid alcoholic drinks" was a good example.

"Our user tests have shown that the word "avoid" can cause confusion and that some people think it only means they should limit their alcohol intake.

"This phrase will now be replaced by the instruction: 'do not drink alcohol while taking this medicine', which is far clearer."

Other recommendations include changing "do not take indigestion remedies at the same time of day as this medicine" to "do not take indigestion remedies two hours before or after you take this medicine".

Another phrase, "do not stop taking this medicine except on your doctor's advice", becomes "warning: Do not stop taking this medicine unless your doctor tells you to stop."

Scientific programming does not compute

An article in Nature explains why scientists need to pay more attention to basic principles of software engineering.

As a result, codes may be riddled with tiny errors that do not cause the program to break down, but may drastically change the scientific results that it spits out. One such error tripped up a structural-biology group led by Geoffrey Chang of the Scripps Research Institute in La Jolla, California. In 2006, the team realized that a computer program supplied by another lab had flipped a minus sign, which in turn reversed two columns of input data, causing protein crystal structures that the group had derived to be inverted. Chang says that the other lab provided the code with the best intentions, and "you just trust the code to do the right job". His group was forced to retract five papers published in Science, the Journal of Molecular Biology and Proceedings of the National Academy of Sciences, and now triple checks everything, he says.—Zeeya Mirali, Nature 467:775—777 (2010)

Spotted by Shriram Krishnamurthi.

Causal commutative arrows and their optimization

Causal commutative arrows and their optimization, by Hai Liu, Eric Cheng, and Paul Hudak, ICFP 2009.

Extends arrows with two widely used concepts, loop and init. Both concepts arise quite often. Proves a normalisation theorem that reduces any program to a single use of loop, and show that in practice this can yield a speedup of two orders of magnitude. Lovely result!

As the paper notes in passing, 'loop' is closely related to the concept of 'trace' from category theory. Phil Scott is currently visiting Edinburgh, and I'm hoping he, Jeff Eggers, and I might explore the relation betwixt 'trace' and 'loop'.

An compelling example of the value of 'loop' and 'init' is the definition of integral:

integral = loop (arr (\ (v,i) -> i + dt * v) >>> init 0 >>> arr (\ i -> (i,i)))

This definition is valid for a stream of events, where each event is separated uniformly by time dt. An intriguing question is how to define integral in a similar style when the time between events is not uniform? Or for continuous behaviours rather than discrete events?

Low floors, low ceilings, and Alice

Matthias Felleisen just introduced me to the phrase "low floor, low ceiling", which characterises precisely the worry about Kodu I expressed in my previous post: languages with a low overhead when getting started may offer low payback later.

As an example of this effect, he suggested the following critique of the innovative Alice programming environment: Through the Looking Glass: Teaching CS0 with Alice. (Thanks to Shriram Krishnamurthi for the precise reference.) I don't consider Alice in the same bowdlerized category as Kodu, so I was surprised to see that "low floor, low ceiling" might still apply.

Meanwhile, Matthias, Shriram, and others offer Teach Scheme/Reach Java as an alternative, offering a curriculum based on widely-used professional programming languages to high school and middle school children. (Addendum: Matthias and Shriram inform me that the TeachScheme website is out of date, and the preferred alternative is Program by Design.)

Pea vs. Papert; Kodu; Bootstrap

Logo, and following on from it Scratch, Alice, and Kodu, promotes an implicit claim that in the right environment children can learn programming almost by osmosis, and that absorbing this skill improves other skills, such as planning. These implicit claims were challenged twenty-five years ago by Roy D. Pea, who discovered that school children exposed to Logo could still be confused by recursion after writing recursive programs, and that learning Logo did not improve their planning ability. Here is an overall summary, here is a paper specifically on recursion, and here is Pea's reply to an attack by Papert.

I found the second paper (Children's mental models of recursive LOGO programs) particularly interesting, as it helps to understand some of the issues my first-year students may face in learning recursion. I'm woefully ignorant of the literature on the psychology of programming, and need to learn more. Thanks to Matthias Felleisen and Emmanuel Schanzer for pointing me at this work.

What sparked my interest was a keynote on Kodu at POPL, by Matthew MacLaurin of MSR. The laudable goal of Kodu is to permit young children to program video games, as MacLaurin put it, 'to let them know the computer can do anything'. And Kodu can achieve quite spectacular results with very simple programs, but the programming model needs to be very simple to achieve this (a list of condition-action pairs). Because Kodu is so special purpose, I worry that instead of teaching children that 'computer can do anything', it will teach them that 'computers will let you build exactly what they are designed to let you build, and anything else is very difficult'. Pea's studies are orthogonal to this concern, so I'm left wondering whether Kodu will lead to a new generation of programmers or a new generation turned off by computing.

Meanwhile, Schanzer is running Bootstrap, an outgrowth of TeachScheme. "Bootstrap is a standards-based curriculum for middle-school students, which teaches them to program their own videogames using purely algebraic and geometric concepts." The start-up costs are higher than Kodu, but once started students have the full power of Scheme/Racket at their command. Seems preferable to me, but there may well be room for both in the world. More study needed! Not to mention more resources for getting proper computing (not just ICT) into schools at an early age.

Happy 2011!

Best wishes for the New Year. (Insert traditional Scottish handshake here.) A special thank you to those who sent pointers to things of interest, some of which I reposted here, and to those who posted comments to the blog. Please keep the good stuff coming!

(Photo by Mike Levad, spotted on Boing Boing.)

The Myths of Object-Orientation

The Myths of Object-Orientation. An after-dinner speech at ECOOP 2008, reprinted in ECOOP 2009. Spotted on Lambda the Ultimate. From the appendix:

The Sing-Song of Old Man Java
With apologies to Rudyard Kipling.

Not always was Java as now we do behold him, but a Different Language with very short types. He was small and he ran slowly, and his hype was inordinate: he danced on a TV set in the middle of California, and he went to Big God Gosling.

He went to Gosling at six before breakfast, saying, ‘Make me different from all other languages by five this afternoon.’

Up jumped Gosling from his fortress on the multicore and shouted, ‘Go away!’

He was small and he ran slowly, and his hype was inordinate: he danced on a set-top-box in the middle of California, and he went to Middle God Steele. He went to Steele at eight after breakfast, saying, ‘Make me different from all other languages; make me, also, wonderfully popular by five this afternoon.’

Up jumped Steele from his virtual reality and shouted, ‘Go away!’

He was small and he ran slowly, and his hype was inordinate: he danced on desktop in the middle of California, and he went to the Little God Gilad. He went to Gilad at ten before dinner-time, saying, ‘Make me different from all other languages; make me popular and able to run anywhere by five this afternoon.’

Up jumped Gilad from his office in Palo Alto and shouted, ‘Yes, I will!’

Instructionless learning about a complex device

If programming language design is to become a science as well as an art, we need to study psychology. This paper describes how subjects worked out (or failed to work out) how to guide 'BigTrak', a programmable toy.

Jeff Schrager and David Klahr, Instructionless learning about a complex device, International Journal of Man-Machine Studies 25(2):153-189, August 1986.

A list is an odd creature, take 6

Not really like a list, but a lovely animated recursion. Thanks to Michel S..

• A list is an odd creature
• A list is an odd creature, take 2
• A list is an odd creature, take 3
• A list is an odd creature, take 4
• A list is an odd creature, take 5

Pionen: WikiLeaks and James Bond

The Daily Mail, of all places, notes that WikiLeaks data is stored at the Pionen data centre in Stockholm. Built inside an old nuclear bunker, it is designed to look like something out of a James Bond film.