Extending C with Prolog (1994)
This 1994 Dr. Dobbs article delves into the complementary strengths of C and Prolog, demonstrating how to integrate them for sophisticated applications. It champions Prolog's declarative power for symbolic AI tasks like pattern matching and search, while C handles procedural elements and system interactions. The piece offers a fascinating historical perspective on language interoperation, appealing to HN's interest in foundational programming paradigms and efficient software architecture.
The Lowdown
The article, originally published in Dr. Dobbs Journal in 1994, provides a comprehensive look at how to effectively combine C and Prolog, emphasizing the unique advantages each language brings to software development. It serves as a guide for C/C++ programmers, offering foundational knowledge about Prolog and practical examples of their integration.
- Prolog's Core Strengths: The author explains Prolog's suitability for Artificial Intelligence due to its integral support for symbols, dynamic memory management, powerful pattern matching (unification), and built-in search (backtracking). These features enable a highly declarative style of programming, significantly reducing boilerplate code for complex logic. Comparisons with C code snippets illustrate how Prolog simplifies control flow and data handling in symbolic operations.
- Declarative Power in Action: Examples include natural language parsing grammar rules and a simple expert system for diagnosing car starting problems, showcasing how Prolog's rule-based nature makes applications more concise and manageable than equivalent C implementations. This allows developers to tackle greater application complexity.
- Interfacing C and Prolog: The article details the architecture of an interface, noting that calls from C to Prolog resemble database queries, while calls from Prolog to C extend its functionality with procedural operations (e.g., I/O). This allows Prolog to leverage C for environmental interactions and low-level tasks it might lack.
- IRQ Expert System Example: A practical example of an IRQ (Interrupt Request) conflict resolution expert system is provided. Prolog embodies the diagnostic knowledge and rules for recommending solutions, while C gathers system information (IRQ assignments) and presents the advice using the chosen user interface. This demonstrates how Prolog handles non-algorithmic knowledge, making the system adaptable and extensible.
- Application Versatility: Beyond the IRQ example, the article suggests numerous applications for this hybrid approach, such as advisor modules for operating systems, financial and tax applications, help desk systems, and natural language front-ends for databases, enabling users to interact with complex systems more intuitively.
Ultimately, the article advocates for a synergistic approach, where Prolog's ability to model and solve complex logical problems is paired with C's efficiency and control over hardware and procedural tasks. This combination, even in 1994, offered a robust solution for building intelligent and flexible applications.