Teaching Programming mk. 2

I blogged before about what I think we should teach programming students, and almost immediately wished I hadn't. Sometimes I feel that my blog posts are somewhat pointless meanderings through the garbage that inhabits my sleep-deprived brain. At other times I feel that I have contributed something useful to the general public. The post in question is firmly in the former category - but what can I do? I won't start deleting articles as soon as I fall out of favor with them, so I'm hereby correcting my earlier mistakes (at least, attempting to). Illiad Frazer knows how I feel:

The whole point of the previous post was that I felt that most graduate students were under-prepared for work in industry. My main evidence of this is that it seems to take a long time, and more importantly a lot of interviews before one strikes "candidate gold" when recruiting for a new programmer.
I will admit that this could be for many reason: perhaps our expectations are too high, perhaps we are not paying enough to attract the kind of graduate we're looking for, or perhaps the industry we're in isn't desirable enough to attract the better candidates. The list goes on endlessly - and yet I cannot ignore the fact that most graduates I meet are not up to scratch.

So what prompted this revision of a past article? I happened to read E. W. Dijkstra's article entitled "On the cruelty of really teaching computing science". In it, he postulates that the methods used by most universities are fundamentally flawed when it comes to teaching computer science, and more specifically when teaching computer programming. I'd like to quote part of this article:

...we teach a simple, clean, imperative programming language, with a skip and a multiple assignment as basic statements, with a block structure for local variables, the semicolon as operator for statement composition, a nice alternative construct, a nice repetition and, if so desired, a procedure call. To this we add a minimum of data types, say booleans, integers, characters and strings. The essential thing is that, for whatever we introduce, the corresponding semantics is defined by the proof rules that go with it.

Right from the beginning, and all through the course, we stress that the programmer's task is not just to write down a program, but that his main task is to give a formal proof that the program he proposes meets the equally formal functional specification. While designing proofs and programs hand in hand, the student gets ample opportunity to perfect his manipulative agility with the predicate calculus.
This method of programming - approaching the programming language as a kind of "predicate calculus' has it's advantages. It demands that the students pay attention to the features, rules, regulations and guarantees that the language provides. Whichever language is used (and to a certain extend it does not matter), the rules and regulations of that language are going to dictate the structure of the program. This is similar to the fact that the laws of math dictate the form of any mathematical proof; ignore the laws of the language, and your program (or proof, if you will) no longer makes sense. In the domain of integer mathematics, 2 + 3 will aways equal 5. In the domain of C++, local variables are destroyed in the reverse order that they were created in (insert whatever rule of the language you want there).

Consider for a moment my previous post; I listed 11 things which I thought were essential for any programming student to know. Looking back, I notice that the top five items are all specific to C++ (since that's the language I talk in). Is it a coincidence that the five most important things any programming student can know are specific to the language they are using? I think not.

Rather, I believe that to be a great programmer, one must have a deep understanding of the language at hand, and how that language allows you to express logical problems. One must approach a program like a mathematical problem - that is, one must know the rules of the language, and then use those rules to design a proof that conclusively solves the logical problem using the language at hand.

That last point is worth reiterating: Anyone can write a program that appears to solve a problem most of the time. However, for non-trivial problems it becomes much harder to guarantee that the program will solve the problem 100% of the time. As we get further into the "edge cases" of the application logic it becomes less likely such a naive implementation will work correctly. However, a program that has been built from the ground up using the guaranteed behavior of the language can still contain bugs, but it's much more likely that they are logic errors introduced by the programmer, rather than subtle bugs introduced through language misuse.

At this point I must point out that I do not believe that Dijkstra's idea is as good as he makes it sound. He addresses one point - that students should understand the rules of the language, but a "love of the language"is only half the picture. There are also many non-language related skills that come in to play. Consider debugging for example; there are formal techniques that can be used to debug certain types of errors. Knowing these techniques, and knowing when to employ them is a powerful aid in any language, and these are skills that should be taught, rather than learned in an ad hoc approach.

So, my revised top 10 list of things every programming student should know can now be revised into this, much shorter form:
  1. Know your language. I don't care what your language is - if you want a job it had better be something that's being used, but you can be a great programmer even if all you know is an out-dated language. Not only do you need to know your language, you need to have a passion for knowing your language - you must actively want to extend your knowledge of the language and how it works, what guarantees it provides and which it doesn't. This knowledge will translate into programs that use the features of the language to create minimal, efficient, well structured and error-free programs.

  2. Be willing to learn new techniques. There are so many useful techniques and skills for a new programmer to have that I cannot list them all here, and course designers cannot possibly include them all in their course material.

That's it - two things. Much better than the self-absorbed tripe I rattled off a few weeks ago. To anyone who actually bothered to read that, I apologize profusely.

3 comments:

DaveB said...

You read Dijkstra in your spare time for kicks?? What next - you got Knuth's set beside your bedside table? (amazon).

Seriously tho - you're "self-absorbed tripe" got a few people back here discussing things. Some items some people thought you were full of it and some people thought you were probably spot on (and for each point there was someone with each of those views). We don't talk about that kind of thing enough - it was good.

Regarding new grads ... I doubt that anyone is ready for working as a programmer without several years full time programming experience. With a grad you're buying a pig-in-a-poke and having to guess which pig will be a high achiever when you've given them some experience.

My advice (take with bucket of salt) is to NOT look for potential in the grad. "Potential" is a mythical promise which you can't rely on. I know many people of high potential who are completely useless. Instead, look for achievement in their life. Do they achieve what they set out to do in hobbies, in their study (well they graduated so I guess that's a given), what are their goals ... but more importantly - what have they done to move closer to those goals.

I'd trade all of my students with high potential for a few who try hard to achieve things. I've seen with students and in real life before teaching - someone with ordinary ability but who takes an interest and works hard will outdo the hugely gifted but couldn't-care-less person.

But that's me getting into "self-absorbed tripe" now

Thomi Richards said...

Good god! You mean to tell me that not only do people read this stuff, they then go ant talk about it in their spare time as well? That's a very worrying thought.

With regards to graduates (or in fact job candidates in general), why can't I have potential *and* achievment? I want the whole bag, the entire package, the real deal...

OK, so maybe that's unrealistic, but we can dream right? Anyway, the point is that any almost-graduates reading this can get an idea of what we need in this industry. I'm by no means suggesting that this is constant across all programming jobs, just this one.

DaveB said...

you might be interested in this interview with Bjarne Stroustrup on computer science education

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