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From: "Jez Higgins"
Date: Thu, January 4, 2007 11:29 am To: "Kevlin Henney" Hi Kevlin, Alongside the normal keynotes, sessions, panel discussions and so on that conferences usually have, the academic conferences I went to as a fresh faced young thing also had poster presentations. A poster presentation was, as you might have guessed, a poster of usually about A3 size, which you filled with whatever you fancied. The posters were usually displayed on freestanding boards in the mingling/coffee drinking areas between the main session rooms. The nice things about doing a poster were it was easier (because you could present a small piece of work, or work in progress), it was cheaper (because you didn't actually have to be there), but you could still list it as a publication. I appreciate this is rather late in the day, but wondered if BoostCon might consider posters? I only bring it up because I doubt I can afford to attend, it clashes with my wife's birthday in any case, but I do have the scrap of an idea for a poster. It would be some little extracts I'd written about Boost.Spirit while working on an XPath and XSLT engine, printed in 72pt text. XPath: variables returning node-sets ------------------------------------ Made a minor grammar fix, and reworked location steps slightly so expressions like $doc/step1/step2 or $doc[pred] work (assuming $doc is bound to a node-set obviously). Everytime I find a problem in the grammar, which actually isn't very often at all, I give thanks to the pragmatic programming Gods that I used Spirit rather than rolling my own parser. In this case, I'd transcribed FilterExpr ::= PrimaryExpr | FilterExpr Predicate after eliminating right-recursion as FilterExpr = PrimaryExpr >> *(Predicate >> PrimaryExpr); rather than FilterExpr = PrimaryExpr >> *Predicate;. Time to fix - about 30 seconds. Time to fix if I'd hand-rolled - don't even want to think about it :) Jaxen Bug 94 - http://jira.codehaus.org/browse/JAXEN-94 -------------------------------------------------------- "Charles Souillard reports a problem while trying to evaluate the following expression : 2+1-1+1. It should be 3.0 but is 1.0" Jaxen is an XPath engine that uses a hand-built parser. It turned out that evaluation order of the arithmetic operators was wrong, and the code had to be patched in many different places to fix it. Since my code implements the grammar as written in the spec, I knew that not only did I not have this problem, I *could* not have this problem. When is an XPath expression not an XPath expression? ---------------------------------------------------- When it's an XSLT pattern, that's when. As an XPath para[@ref] selects, for a given node, its child para elements which have ref attributes. As an XSLT pattern it tests whether a given node is a para element which has a ref attribute. Similarly, something like chapter/para tests whether a given node is a para element with a chapter element parent. In XPath terms, you'd express this as something like boolean(self::para[parent::chapter]). Aside from this sematic difference, syntactically XSLT patterns are an XPath subset. I don't have these things evaluating yet but, thanks to the miracle that is Boost.Spirit, I've extended Arabica::XPath to parse them. Took about half an hour, including writing a pile of test cases and getting them passing. Spirit really is a top piece of work. While it's not hard to find people rambling on about how Python or Lisp or whatever really is the thing for writing little domain specific languages, this kind of thing really shows just how deadly cool template metaprogramming can be. Read the EBNF, transcribe it into code, compile, and go. Easy, expressive and type-safe. What more could you want? Yes, it's a love letter to Spirit. Why not? Hope you're keeping as busy as you'd like, and that you and your family are well and happy. Jez
390-055. I am in it!
Much as I love Stevie Nicks, if Fleetwood Mac ever tour again I will go to see them because Mick Fleetwood always looks like he's having a complete ball. Here they are doing The Chain in 1979.
You get glimpses of him in the background of this performance of Go Your Own Way. Thirty years later and he's still having a brilliant time.
I want to be in a room when a man who's been doing it his entire life is still that excited to be playing drums.
I'm going to go out on a limb and declare this year as outrageously anomolous. Let's see what happens next year.
Harry Higgins - West Midlands Tumbling Champion. Really quite proud.
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