Preface

The design and implementation of Phoenix is highly influenced by FC++ by Yannis Smaragdakis and Brian McNamara and the (Boost Lambda Library) BLL by Jaakko Järvi and Gary Powell. Phoenix is a blend of FC++ and BLL using the implementation techniques used in the Spirit inline parser.

Is Phoenix better than FC++ or BLL? Well, there are concepts found in Phoenix that are not found in either library. FC++ has rank-2 polymorphic functions ( FC++ jargon) which Phoenix also has, BLL has syntactic sugared operators which FC++ lack, that Phoenix also has.

Phoenix inherits FC++'s rank-2 polymorphic functions. Rank-2 polymorphic functions are higher order functions that can accept polymorphic arguments. FC++ is the first library to enable higher order polymorphic functions. Before FC++, polymorphic functions couldn't be used as arguments to other functions.

What really motivated the author to write Phoenix is the lack of access to a true stack-frame with local variables (closures) in all C++ FP libraries in existence so far. When emulating functions in the form of functors, the most basic ingredient is missing: local variables and a stack. Current FP libraries emulate closures using state variables in functors. In more evolved FP applications, this "poor man's closure" is simply inadequate.

Perhaps BLL does not need this at all since unnamed lambda functions cannot call itself anyway; at least not directly. FC++ arguably does not need this since it is purely functional without side-effects, thus there is no need to destructively write to a variable. The highly recursive nature of the Spirit framework from which Phoenix is a derivative work necessitated true reentrant closures. Later on, Phoenix will inherit the Spirit framework's true closures which implement access to true hardware stack based local variables.

Phoenix is also extremely modular by design. One can extract and use only a small subset of the full framework, literally tearing the framework into small pieces, without fear that the pieces won't work anymore. For instance, one can use only the FC++ style programming layer with rank-2 polymorphic functions without the sugared operators.

Emphasis is given to make Phoenix much more portable to current generation C++ compilers such as Borland and MSVC. Borland for example chokes on both BLL and FC++ code. Forget MSVC support in FC++ and BLL. On the other hand, although Phoenix is not yet ported to MSVC, Phoenix uses the same tried and true implementation techniques used by the Spirit framework. Since Spirit has been ported to MSVC by Bruce Florman (v1.1) and by Raghav Satish (v1.3), it is very likely that Phoenix will also be ported to MSVC.

Finally, and most importantly though, Phoenix is intended, hopefully, to be much more easier to use. The focus of Phoenix (and Spirit for that matter), is the typical practicing programmer in the field rather than the gurus and high priests. Think of Phoenix as the C++ FP library for the rest of us

Copyright © 2001-2002 Joel de Guzman

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