C++ and functional programming

What to say to C++ programmers about functional programming, especially now that many compilers have implemented C++0X features like lambda and auto. I am pretty good at C++, having started using it with the Zortech compiler V1 and the first versions of CFront (the orginal C++ to C translator). I have also written much fancy template code. Therefore thinking about this post leaves me in the dilemma that there is one part of me that likes the features of C++0X that "wrap up" loose ends, and another part of me, the functional programming part, that makes me want to rant! I will not rant today, but part of that reasons for being upset needs to be said, as is relevant. The "magic" of mature functional programming are:

• Statements, expressions, functions and types support each other
• Type inference and polymorphism automate the relation between statements, expressions, functions and types
• Monadic and other "advanced" types are available to define new execution models such as parallelism.

C++ templates can bee seen as a primitive functional language. But I would argue against going into production focusing on C++ templates that way as I have been burnt so many times by C++ compilers failing me with complex templates, not to mention the difficulty to hire for this skill So template functional style is not where the emphasis should be. The real issue is that although C++ expressions have a C++ type counterparty (think operators like + and -), there is no C++ type support for statements. As a result many of the core concepts of functional programming cannot mapped across C++, even with the new C++0X features of lambda, garbage collections, auto, etc. My recommendation is that some concepts should be understood by C++ developers but not necessarily with a functional emphasis. My favorite topic is as always monads. In the C++ terms, monadic concepts define properties on the "traces" of the code. If we say: f(...); g(...); then the execution trace of the program will first have gone through f and therefore when g is called, properties set by f may still be valid. A good C++ architect should understand enough about monads to define invariants that can be used in this type of trace oriented context. For the moment, I would forget about other "functional programming concepts" in C++, even if it is C++0X!