Communications - February 2011

persistence over time. A computer language also concerns communicating with the computer.

Kamp seemed to conflate the formal syntax of a language with a variety of presentation and communication issues in programming environments, rather than with the language itself. His examples even demonstrated my point; no matter what the formal syntax, contemporary tools can overlay useful semantics, making it much easier for humans to express their ideas. Why in the world would we want to enshrine the vagaries of human perception and cognition in the syntax of a computer language?

I also have reservations about many of Kamp’s suggested improvements. He clearly privileges “expression” over “communication,” and his reference to using color and multi-column layouts is highly problematic. These concepts make assumptions about the technical capabilities available to users that are as likely to change as the perceived technical constraints that led to the syntax of C. Despite his intention to be provocative, Kamp was also quite conservative in his technological assumptions, staying with two dimensions, eschewing sound, ignoring handheld technology, and generally expecting WIMP interfaces on commodity PCs.

I find the biggest problem with programming languages involves understanding, not expression. I’m probably typical in that I’ve read far more code than I’ve written, most of it by strangers in contexts I can only guess. Many of my toughest challenges involve unraveling the thoughts of these other programmers based on limited evidence in the code. For the reader, adding color coding, complex nonlinear texts, and thousands of glyphs means only more cognitive load. It’s difficult enough to “execute C/Java/etc in my head”; mapping complex, multicolored hypertext to formal logic only makes it more difficult.

Kamp made a great case for why hu-
mans should never see programming
languages, just like they should never
see XML or RDF. They should express
themselves through environments that
promote communication by humans,
with the added ability for the machine
to generate correct code (in multiple
languages) as needed. While such
communication could be implement-
ed through a programming language,
the language itself would need features
not generally found in conventional
languages, including semantics (not
easy to define or express) that model
displays and layouts.

Author’s Response:

As desirable as McGrath’s vision might be, in a trade where acrophobia is the norm, giant leaps may be ineffective. So while others work on the far future, I am happy to start the stairs that will eventually get us there.

Poul-Henning Kamp, Slagelse, Denmark

ton, CA); Graziano, Peter J. (Los Altos, CA); Green, Michael D. (Los Altos, CA); Greig, David A. (Cupertino, CA); Hayas-hi, Steven J. (Cupertino, CA); Mackie, David R. (Ben Lomond, CA); McEvoy, Dennis L. (Scotts Valley, CA); Treybig, James G. (Sunnyvale, CA); and Wieren-ga, Steven W. (Sunnyvale, CA).

Armstrong also said, “Adding transactions is easy,” then sketched an implementation. While the implementation may be useful in the telecom world, it does not handle the durability provided by database transactions; see, for example, Gray and Reuter. 3

Paul mcJones, Mountain view, CA

References

1. Bartlett, J.F. A ‘nonstop’ operating system. In Proceedings of the Hawaii International Conference on System Sciences (1978), 103–119.

2. Gray, J. Why Do Computers Stop and What Can Be Done About It? Technical Report 85.7. Tandem Computers, Inc., 1985.

3. Gray, J. and Reuter, A. Transaction Processing: Concepts and Techniques. Morgan Kaufman, 1993.

4. Katzman, J.A. System architecture for NonStop computing. CompCon (1977), 77–80.

credit Due for tandem’s Hardware and os Joe Armstong explained in his article “Erlang” (Sept. 2010) how a programming language originally developed for “building high-performance telecom switches” is today used for a range of high-availability, scalable applications, but I would like to clarify two parts of that explanation: The first was saying, “This technique was used by Jim Gray2 in the design of the fault-tolerant Tandem computer.” Gray made major contributions at Tandem, but by late 1980, when he joined the company, its fundamental hardware and operating system fault-tolerance techniques were already established. Assigning credit accurately for the various aspects of a large and complex system design (such as Tandem’s NonStop systems) may be tricky, but Barlett1 and Katzman4 were key contributors to the hardware and the operating system, respectively. Bartlett’s paper acknowledged Dennis McEvoy, Dave Hinders, Jerry Held, and Robert Shaw as contributing to design, implementation, and testing. Finally, the co-inventors listed on the first patent granted on the Tandem system, 4,228,496, October 14, 1980, filed September 7, 1976, were: Katzman, James A. (San Jose, CA); Bartlett, Joel F. (Palo Alto, CA); Bixler, Richard M. ( Sunnyvale, CA); Davidow, William H. ( Atherton, CA); Despotakis, John A. (Pleasan-

Author’s Response:

McJones is correct in saying the transactions described in my article are nondurable. Database transactions with ACID—atomicity, consistency, isolation, durability—properties are provided by the mnesia database included in the Erlang distribution. The purpose of that section was not to cover kinds of transactions but to show the ease a particular type of nondurable transaction involving an in-memory reversion to an earlier state could on failure be accomplished through single-assignment variables.

Joe Armstrong, Stockholm

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