{"id":1064,"date":"2010-05-08T18:11:40","date_gmt":"2010-05-09T01:11:40","guid":{"rendered":"http:\/\/boost-spirit.com\/home\/2010\/05\/08\/next-week-is-boostcon-week\/"},"modified":"2010-05-10T06:17:53","modified_gmt":"2010-05-10T13:17:53","slug":"next-week-is-boostcon-week","status":"publish","type":"post","link":"http:\/\/boost-spirit.com\/home\/2010\/05\/08\/next-week-is-boostcon-week\/","title":{"rendered":"Next Week is BoostCon Week!"},"content":{"rendered":"

Finally, the long wait and the preparations for BoostCon 2010<\/a> are over. The last weeks were dominated by writing the code and creating the slides for our talk ‘A Framework for RAD Spirit<\/a>‘. Regular readers of this site probably have already wondered why we have been inactive here since mid-March. Well, that is mainly because of preparing for BoostCon turned out to be too time consuming to leave any room for writing posts and articles.<\/p>\n

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Our\u00a0 talk (Joel’s and mine) is about the current status and the preliminary results we achieved while working on the compiler project announced earlier<\/a>. We settled for applying a Scheme based framework to create a rapid development environment for Spirit parsers. This is a really exciting project which will have long term impact not only on Spirit.<\/p>\n

Here is a sneak preview of what we will present at BoostCon.<\/p>\n

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As you can see, we created a kernel consisting out of a cool data structure called U-tree (essentially a discriminated union), capable of storing any\u00a0 S-expression. On top of this Joel developed a Scheme compiler\/interpreter which first constructs a dynamic expression tree from the S-expression (the compiler) conforming to the usual Scheme execution rules. Executing this expression tree yields the result encoded in the Scheme code which has been stored in the S-expression in the first place (the interpreter).<\/p>\n

As a byproduct of this we got the beginnings of a new library \u2013 the dynamic counterpart of Boost.Phoenix<\/a>. It is aimed at dynamic execution trees based on functional programming paradigms. So the Scheme compiler creates a functional data structure which is indistinguishable from an equivalent data structure created from a C++ expression built on top of this new library.<\/p>\n

In order to fill the S-expression from Scheme code we developed a Spirit based parser. OTOH, the Scheme generator (written using Karma – what else?) takes any S-expression and converts it back to the equivalent Scheme code.<\/p>\n

The (currently) top most layer of the framework consists of a Parser for Qi expressions which creates an S-expression and a corresponding generator converting any S-expression holding a Qi parser back into the equivalent Qi (C++) expression. Naturally, the Qi parser is written using Qi and for the Qi Generator we utilized Karma. The Qi compiler mentioned in the figure takes such an S-expression and produces an execution tree, which \u2013 when actually run – parses any input conforming to the initial Qi grammar.<\/p>\n

I don’t want to spoil the fun and tell too much at this point, but overall this is not only a nice example of how to write more complex Spirit applications, but it gives you a rapid development platform allowing to quickly test Qi parsers. Moreover, as the whole thing is based on a Scheme kernel, you can write your own Scheme code for additional transformations of the handled S-expressions. In the context of the Qi based S-expressions mentioned above this is equivalent to dynamic parser transformations or arbitrary parser analysis modules. That is pretty powerful stuff!<\/p>\n

Joel and I plan to write about what we developed and what we learnt while developing this and we hope to get some of you interested to chime in. There is still a lot to do, we are by no means done with this framework. And, as I mentioned already, I believe this will have an impact far beyond its initial target audience.<\/p>\n

But BoostCon is not only about Spirit (even if there will be at least 3 talks about it). We will have a full week packed with sessions presented by well known Boost people speaking about a whole set of interesting topics. Just have a look at the BoostCon schedule<\/a> to convince yourself. Over the next week I will try to document some of my impressions live from the Physics Center in Aspen (where BoostCon takes place). So stay tuned!<\/p>\n

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