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Getting Jiggy with Proto - Boost'Con 2011 Tutorial Hands-on Session

Contents and Objectives

Embedded Domain Specific Languages (EDSL) are actually rising as a design of choice to handle small to middle sized problem in a declarative and efficient way. Among others, C++ is actually a pretty interesting choice as a host language for such development. Idioms like Expression Templates have been demonstrated to be the technique of choice for such situation. However, they always look like some dark arcane secrets and scare potential developers away.

Thanks to libraries like Boost.Proto, the design and development of Expression Templates is becoming easier and easier. More than Expression Templates, the main strength of Proto is to enable compiler-like code to be written and applied on lazily evaluable expression. Combined to the flexibility of C++ in terms of operator and function overloading, making EDSL that works and are not a mess to maintain is possible.

This three hours tutorial will try to cover the basic and intermediate ground of Proto and will demonstrate that writing Proto enabled code is not that scary. The chosen subject is somethign simple : analytical derivation of functions and their evaluation. This is a subject I think many people here will be familliar of (or will be quickly refreshed on) and yet give a lot of opportunity as a tutorial.

I strongly hope the ''Take Away Home'' element of this session will help spreading the use of EDSL as a C++ library design technique and clarify what Proto is and is not.

Structure of the Tutorial

Introduction - Boost.Proto in a (meta) nutshell

This introduction will present the basic concepts behind Proto, how it can be used to model and implement EDSL within C++. Focus will be put on the notion of Expression, Grammar, Domain and Generator which are the very basic building blocks of Boost.Proto. We end up this part by giving an example that will lead us to the hands-on part: designing a small grammar and expression system able to handle simple arithmetic computations.

Part 1 - My Calculator is Rich

First hands-on part will be to extend the initial examples from the Introduction to produce a working calculator. We'll introduce the notion of Transform and we'll build a transform to be able to evaluate a given arithmetic expression for a given value. At the end of this part, we should end up with a small analytical function EDSL able to evaluate arbitrary expressions.

Part 2 - Computing Analytical Derivatives

The second part will look at how Transforms can be used not only to evaluate Expressions but how they can actually restructure them. We'll tackle on the problem of computing the analytical derivative of a given expression using the good ol' derivation rules. We'll see how various details of the derivation process will lead us to define new elements in our grammar and how those simple rules can actually be extended to support partial derivation. After this part, our small calculator should now support arbitrary partial derivative of multiple variables functions.

Conclusion - We Finally Made It !

At the end of the tutorial, we'll end up with a fully functional and extensible analytical function EDSL supporting derivatives and partial derivatives, a way to simplify and evaluate expressions and a small extension mechanism. This tutorial will have covered the main parts of Boost.Proto how it interacts with other Boost components.

Useful Links

Boost Getting Started:http://www.boost.org/doc/libs/release/more/getting_started/index.html
Boost.Proto Documentation:http://www.boost.org/doc/libs/release/doc/html/proto.html
Boost.Proto talk by Eric Niebler - Boost'Con 2010:http://boostcon.blip.tv/file/3970405/