More expressive loops for Eiffel

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New variants of the loop construct have been introduced into Eiffel, allowing a safer, more concise and more abstract style of programming. The challenge was to remain compatible with the basic loop concept, in particular correctness concerns (loop invariant and loop variant), to provide a flexible mechanism that would cover many different cases of iteration, … Read more




The theory and calculus of aliasing

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Thus we are permitted to prove that the unqualified call creates certain aliasings, on the assumption that it starts in its own alias environment but has access to the caller’s environment through the inverted variable, and then to assert categorically that the qualified call has the same aliasings transposed back to the original environment. This change of environment to prove the unqualified property, followed by a change back to the original environment to prove the qualified property, explains well the aura of magic which attends a programmer’s first introduction to object-oriented programming.







Just another day at the office

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In the past few weeks I wrote a program to compute the aliases of variables and expressions in an object-oriented program (based on a new theory [1]). For one of the data structures, I needed a specific notion of equality, so I did the standard thing in Eiffel: redefine the is_equal function inherited from the … Read more




Touch of Class book page available

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The book page for Touch of Class (my introductory programming textbook), announced in the book, is finally available, courtesy Vladimir Tochilin: touch.ethz.ch It includes some book extracts (prefaces, table of contents, an entire sample chapter, for which I chose the Recursion chapter), a list of known errata and a wiki page to report new errata, … Read more




Dwelling on the point

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Once again, and we are not learning! La Repubblica of last Thursday [1] and other Italian newspapers have reported on a “computer” error that temporarily brought thousands of accounts at the national postal service bank into the red. It is a software error, due to a misplacement of the decimal points in some transactions. As usual … Read more




The Case of the Handsome Couple

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Yesterday’s New York Times carries an article by John Tierney about the 95th anniversary of the king of mathematical puzzles, Martin Gardner. The article is so well done that I will not even try a summary, referring you instead directly to it [1]. Just one detail worthy of note:  when he undertook to write a … Read more




The CPU Clock principle of software releases

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On how to build software, there is still much we do not know for sure; but we have also learned a few principles that can be considered firm.  By definition these are not new ideas; today’s principle, for example, is related to what agile developers know as “timeboxing”. But even if they have been published … Read more