Hi, all, Unification and backtracking are the two key concepts of Prolog language. Prolog language is one of the preferred ways to develop "intelligent" software. I am wondering how many people here are interested in a Boost Unification and Backtracking Library (UBL). UBL will implement the unification and backtracking feature with the help of both preprocessor meta-programming (Boost Preprocessor library) and template meta-programming (MPL). With UBL, you will define Prolog-like predicates right inside your C++ code. ========== Why do we need it? =========================== 1. a C++ and Prolog combined solution may not be convenient. You need to write a lot of wrapper code to allow bi-directional communications between Prolog code and C++ code. Standard Prolog is not an Object Oriented Programming Language. As such, you need to write even more code to allow Prolog to access C++ class instances. Worse yet, each prolog implementation has its own way to interface with foreign languages. So your wrapper code most likely would not be portable to other Prolog implementations. 2. Unlike C++, Prolog is not strong-typed. Folks in the C++ land too long may not like anything that is not strong-typed. 3. C++ is a multi-paradigm language. At beginning, it was procedure oriented. Then it's object oriented. During the past few years, functional oriented programming in C++ and even aspect oriented programming in C++ become hot topics and real possibility. Now why don't we give C++ a logic programming flavor? 4. UBL allows the programmer to switch back and forth among the multi-paradigm seamlessly, therefore make it easier to combine the right features of each paradigm to solve a given problem. Better yet, you do not need to lean a new language (Prolog). =========== Is UBL feasible?=================== The short answer is yes. I already have the prototype up and running in VC++ 7.1. The 8-queen problem takes less than 28 seconds on my Athlon 2200+ to find all answers. The prototype does have its fair share of shortcomings: 1. template based metaprogramming in general, and the prototype of UBL in particular, takes too long to compile any non-trivial code. Or may not be able to compile at all. 2. syntax wise UBL predicates are not as straight-forward or visually appealing as the equivalent predicates in Prolog. Here is a predicate in UBL: BOOST_UBL_PREDICATE_2_( is_grandfather_of, Person, Person ) { BOOST_UBL_VARIABLES_3 ( Person, X , Person, Y , Person, Z ); typedef clause< LHS<X, Y> , is_father_of< X, Z > , is_father_of< Z, Y >
type; };
Here is the equivalent predicates in Prolog: is_grandfather_of(X, Y) :- is_father_of(X, Z), is_father_of( Z, Y). 3. In my plan, the Lambda library will provide the "fast-lane" between UBL and your C++ instances, member functions and member variables. Of course, that is not done yet.