Archive for the ‘Programming’ Category

Is Software Engineering Possible?

June 7, 2017

When the textile industry arose in the 18th century, craft was the norm in manufacturing. As the industrial revolution progressed, one after another sector of the economy made the transition from craft to industry. In 1968 it was noticed that the creation of software was a craft in a world where industry was the norm. In that year a conference was convened to address that anomaly. Those present saw themselves as participants in a momentous occasion: after this conference, Software Engineering existed, which was not the case before.

In the final paragraph of my 2009 article “Software Engineering: From Craft to Industry?” [8], I ventured to disagree. From the final paragraph:

While the processing of material leaves an irreducible residue of work for humans, in the processing of information any work that is routine instantly vanishes. Extracting the routine part from an information processing task is a creative endeavour. It is called programming. In the building of a software system any time you think you have something routine to be handed over to managed cubicle-dwelling drones, [9], you are missing an opportunity for automation. In the building of a software system there is only room for creative work. It is Craft, irreducibly so.

At the time I had read John Allen’s “Whither Software Engineering?”. I found it fascinating, but dismissed it as unrealistic and I was not convinced of its urgency. This article explains why I changed my mind.

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Programming by Gathering Snippets of Truth

May 13, 2017

Xavier: What is logic programming?
Yorick: Robert Kowalski defines it as a certain approach to knowledge representation, namely

Logic programming shares with mechanical theorem proving the use of logic to represent knowledge and the use of deduction to solve problems by deriving logical consequences. [1]

X: Ah, I see—a kind of Artificial Intelligence, which I am not so much interested in. Yet, I find a lot of interesting stuff in Logic Programming, the journal, in its first decade, and in several books of that time, Sterling and Shapiro’s The Art of Prolog and O’Keefe’s The Craft of Prolog. Why listen to Kowalski anyway?

Y: He invented “Logic Programming” as a term and substantiated his definition with his book [2]. Moreover, his “Predicate logic as a programming language” [3], established him as a co-inventor, with Colmerauer, of pure Prolog.

X: It seems that the term “Logic Programming” has been hijacked by people interested in what makes Prolog different from other programming languages and in how logic can be used as starting point in the design of programming languages.

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Children of the Miracle: from Algol to Prolog

March 18, 2017

The appearance of Fortran inaugurated a fruitful period in programming languages that was to last until the early 1970s. When, in 1999, E.W. Dijkstra gave the keynote address at the ACM Symposium on Applied Computing in San Antonio, Texas, he gave an overview of what he saw as the large-scale trends in the preceding half century. I quote:

And then the 60s started with an absolute miracle, viz. ALGOL 60. This was a miracle because on the one hand this programming language had been designed by a committee, while on the other hand its qualities were so outstanding that in retrospect it has been characterized as “a major improvement on most of its successors” (C.A.R. Hoare).

Several friends of mine, when asked to suggest a date of birth for Computing Science, came up with January 1960, precisely because it was ALGOL 60 that showed the first ways in which automatic computing could and should and did become a topic of academic concern. [1]).

Algol was a miracle as a language. It was short-lived, but it left a momentous legacy that acted in two ways: in the way the Revised Report on Algol 60 describes the language and in the way subsequent language designers were influenced by being shown what a programming language could be. In celebration of Algol 60 I refer to these designers as “Children of the Miracle”.

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The Essence of Algol

November 12, 2016

Elsewhere [10] I considered ways in which programming languages could be different. One of these ways is expressed by asking the question Does the language have an essence? The possibility of an affirmative answer is suggested by the title of John Reynolds’s paper: “The essence of Algol” [7]. Reynolds used what he perceived to be the essence of Algol to make distinctions among members of what is usually considered to be a single family. Thus he argues that Algol 60 is a carrier of the essence, whereas this is not the case for other members of that family: Algol W, Euler, Algol 68, and Pascal.

What is judged to be essence is in the eye of the beholder. I am more interested in what the members of the Algol family have in common and perhaps even with languages not usually considered as members. For example, Prolog. Soon after completion of this language in Marseille, Robert Kowalski wrote a paper (published as [6]) that established a procedural interpretation of a form of first-order predicate logic. Let us examine this interpretation to see whether this gives a hint concerning the essence of Algol as a procedural language.

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Kinds of Programming Languages

October 21, 2016

I find the number of programming languages mind-boggling. For example, Jean Sammet in her “Roster of programming languages for 1976-1977” [12] lists 156 programming languages in 24 categories. This includes only languages in active use within the USA. The opposite extreme on the spectrum of permissiveness is represented by the “Online historical encyclopedia of programming languages” [7], which claims 8945 “programming languages since the 18th century”.

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Some Books on C

March 26, 2016

I have gathered such introductory books on the C programming language as I own or could borrow. The result is an eight-storey tower. A quick scan shows that I could easily buy another half dozen, but I doubt whether that would yield any new insights.

For most teachers “an introductory programming book with C” is an oxymoron. The extreme wing in this school of thought consider only designedly friendly languages suitable for an introduction to programming. BASIC is an early example. My current favourite friendly language is Python [1]. But the mainstream of teachers of introductory programming has settled on Java as a compromise between friendliness and attractiveness to prospective employers.

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Why does C not have an exponentiation operator?

March 15, 2016

The most authoritative source for an answer to the question in the title would be Dennis Ritchie. Next best is Bjarne Stroustrup:

The semantics of C operators should be simple to the point where each corresponds to a machine instruction on a typical computer. An exponentiation operator doesn’t meet this criterion. [1], page 247

Stroustrup’s criterion needs to be taken with a grain of salt. For example, the assignment operator does not meet the criterion: a = b takes a LOAD and a STORE. In this case the criterion translates to: “should correspond to no more than a LOAD and a STORE. But Stroustrup was onto something, because we can tweak his answer to:

The semantics of C operators should be simple to the point where they each compile to code that is as fast as what one can write in assembler.

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Recursion versus iteration

July 30, 2014

The first programming language to allow functions to be recursively defined was McCarthy’s LISP in 1959. Its introduction was not controversial: nobody but John McCarthy had any say in what the language was going to be. In addition to his work on LISP, McCarthy was on the committee finalizing the Algol language in 1959 and 1960. In spite of the fact that a majority was opposed to it, the definition of Algol 60 ended up allowing recursively defined procedures. In [1] I gave an acount of how this happened.

Why was recursion such a big deal? For us this is hard to understand: for decades the programming language C, not exactly a paradigm of avant-garde, has allowed recursion. Still, remnants of unease remain. Still, in some introductory courses, recursion plays the role of a pons asinorum. Have instructors been traumatized by a sarcastic teacher finding, oh horrors, a circular definition in their high-school essay? In this essay I’m going to explore recursion by contrasting it to its opposite, iteration.

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How recursion got into programming: a tale of intrigue, betrayal, and advanced programming-language semantics

June 18, 2014

By now it is difficult to imagine that once there was a time when the utility, and even the possibility, of recursion in programming was in doubt. Yet that was true of the programming community around 1960. Even the committee that was to create Algol 60 was divided on the issue. How recursion got into the language is a story of intrigue and misunderstandings. I came across this story for the first time when reading Gauthier van den Hove’s excellent MSc thesis [11]. It is also the subject of Chapter 3 in [12].

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Dijkstra, Blaauw, and the origin of computer architecture

June 14, 2014

E.W. Dijkstra is known for several important contributions. It does not seem to be widely known that he played a role in the origin of computer architecture as a concept. In arguing that this is the case I draw attention to the passage in his 1972 Turing lecture where he recounts that the darkest week in his professional life was when he studied the specifications of a newly announced line of computers that he does not further specify than being “of the third generation”.

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