Ole-Johan and Kristen: some personal reminiscences

I had the pleasure of working at the Norwegian Computing Centre (NR) from 1968-1973. It left an indelible impression. By time I arrived, Ole-Johan had left to work at the University, but I got to know him through working on the Simula begin text The weekly ritual was for me to arrive on Friday afternoon. Ole-Johan would then read another chapter and put it right (rather than merely correct it). He had a wonderful gift for taking in my mundane prose and improving it enormously by gently adding in a sentence here, a felicitous phrase there, . . . And always gently encouraging: only twice did he bite the end off his pipe at the crassness of the rubbish I had written. He could have done so many more times.

I soon learned to admire both his elegant programming and his writing skills and benefitted greatly from access to drafts of his famous papers with Hoare in the Structured Programming text and with Wang in BIT. Both repay study today.

One week he took my offering, propped his feet on his desk, and toppled a veritable steeple of texts onto the floor. When we came to restack them, we found a cheque made out to him for 1000 Nkr (quite a handy sum in 1970) --- and a year old. "Ah yes", he said, "I was wondering where that had got to".

After leaving NR in 1973, I spent the rest of my career in academia. The OJD influence remained strong and I used his masterful 1970's notes and texts to teach operating systems, parsing, and run time structures for block structured programs many times to many students. In the 1980's I was using his model of an OS kernel described in Simula to put across processes, interrupts, and semaphores to some very bright students at Calgary. After lecture 1 of 4 on the topic, a few came up to me and said this would be a waste of time as they had covered this stuff twice before. I asked them to trust me (meaning trust Ole-Johan). After lecture 4 they came back and apologised -- "You were right. We really didn't understand the stuff before but we do now". Thanks Ole-Johan.

Kristen came directly into the picture at NR where I helped out with some early Simula courses as part of my duties. I thought I understood programming on arrival, but my first glimpse of Kristen in action using his paper-and-pencil model of Simula execution put me right. So that's how variables get bound and procedures and recursion work (never mind the objects!). I have used this model ever since and heartily recommend its use right from the start on (just about) any and every programming language course.

As an aside, I gave a seminar on Simula at KTH in the early 1970's. When I used Kristen's model to explain the (Algol) binding rule, a member of the audience stood up and said that this was complete nonsense and left the room. 15 minutes later he was back. He had run the program and found it worked as stated. He apologised and asked if it would be ok to come back. I often wonder what the audience would have made of the talk had he not come back. What a gentleman. What a model.

Have you ever wondered why objects are called objects? Here is my guess --- sadly I was going to check this out with Kristen the next time we met. Kristen has always been a great searcher for le mot juste. In the 1960s his bible was a thick (12cm or so) volume of Websters. Look up system there and you find:

an assemblage of objects arranged in a regular subordination, or after some distinct method, usually logicial or scientific;
. . .
a complete whole of objects related by some common law, principle, or end;
a complete exhibition of essential principles or facts, arranged in a rational dependence or connection;
a regular union of principles or parts forming one entire thing;

So was Webster a precog in 1913 -- or was that the source for Kristen's usage?

Whilst at NR Kristen kindly took me and my family along with many other waifs and strays into his heart and into his family, and we enjoyed many happy hours in their company.

After I left NR, Kristen kept in touch and would appear from time to time to see how things were and pass on his current enthusiasms. The last time we met was not so long ago. As ever he was bubbling with excitement, thrilled to bits that the COOL grant was about to start, and already thinking about 3 other research directions he had to wrap up. Not bad for 75.

We oldies remember the good old days of the 1960's and 70's when hardly anyone gave a damn about objects. As a last aside, in 1960 I worked for one of the UK's grand old men of simulation, Tocher, for the summer. When I next saw him in 1974 I told him where I had been and he responded "Nygaard and Dahl. What's happened to them? They blazed onto the scene like comets in the early sixties, and then just vanished." Not quite, fortunately. I then tried to congratulate Tocher on using objects in the 1950's to structure his models (this he did calling them activity cycles. Tocher coded in octal not even assembler and resorted to an activity based simulation control structure). At this he blew his top and offendedly pronounced objects complete and utter rubbish.

But our heroes were not in oblivion. They kept the faith and have been justly rewarded in the last couple of years receiving the recognition they truly deserved. As we would never have guessed nor wanted, it was just in time. But it was in time and they had the chance to receive and cherish that great warmth and respect in which they were held by the computing community worldwide.

So farewell then to two men who were not only great scientists, but also good men. They revelled in their families, challenged each others intellects in demanding but constructive ways, and delighted in training up new generations of youngsters to stand on their shoulders and see further. See further? fat chance in my case.

The torch is now ours to pass on --- let us not fail them.

- Graham Birtwistle,Aug. 14, 2002