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Related issues

Information and scripting

I have seen proposals to use XML in a scripting language context.  While I have no fundamental problem with this, I have mild concerns that widespread use of XML in this way could lead to muddying of the distinction between commands and content.

25 years on from Backus' seminal paper "Can programming be liberated from the von Neumann style?" [10], applications of XML data are emerging that provide real scope for the kind of functional programming style advocated by Backus. But using the functional style in a procedural context can be less easy, as a fundamental tennet of functional programming, from which it derives much of its expressive power, is the lack of side effects visible within the programming language constructs.  It is far easier to prove properties about data and transformations on data in the absence of side effects.  As systems become more complex, I believe the kind of transparency associated with provability will become more important.

Therefore, I urge that XML designs for encoding procedural information should take care to separate this from non-procedural data that may be the fodder for such procedures.

[10] John Backus, Can programming be liberated from the von Neumann style?: a functional style and its algebra of programs. Communications of the ACM, Volume 21, Issue 8  (August 1978).  Citation: http://doi.acm.org/10.1145/359576.359579 .  Document at: http://www.stanford.edu/class/cs242/readings/backus.pdf .