MDL: The MIT Design Language – A Pioneer in Programming Language Evolution
The world of programming languages has witnessed tremendous growth and evolution over the years, but some languages stand out for their pioneering features and lasting influence. One such language is MDL (MIT Design Language), which played a significant role in the development of modern computing and the broader world of interactive fiction. Although MDL is now obsolete, its impact continues to be felt in various areas of programming, particularly in the fields of artificial intelligence, multithreading, and interactive storytelling. This article delves into the history, features, and legacy of MDL, exploring its origins at MIT, its contributions to programming languages, and its enduring influence on the development of modern technologies.
Origins of MDL: A Product of MIT’s Project MAC
MDL was developed in 1971 at the Massachusetts Institute of Technology (MIT) as a high-level programming language for the Dynamic Modeling Group, a part of MIT’s Project MAC. Project MAC was a research initiative aimed at advancing computing technologies, particularly in the areas of artificial intelligence, time-sharing systems, and interactive computing. MDL was originally designed to provide support for the group’s work, which involved creating dynamic models of systems and processes.
The development of MDL was spearheaded by a team of influential researchers, including Gerald Sussman and Carl Hewitt from MIT’s Artificial Intelligence Laboratory, as well as Chris Reeve, Bruce Daniels, and David Cressey from the Dynamic Modeling Group. These individuals were pioneers in the field of computer science and played pivotal roles in shaping the early years of artificial intelligence and programming language design. As the project progressed, other contributors, such as Stu Galley, helped document MDL and solidified its place in the history of programming languages.
The Birth of MDL and Its Original Name: “Muddle”
Initially, MDL was known by a different name: Muddle. The choice of the name “Muddle” was in line with the playful, self-deprecating humor that was prevalent within the MIT research community at the time. The name was a tongue-in-cheek reference to the complexity and sometimes chaotic nature of the language. However, the name “Muddle” did not resonate well with the broader computing community, and it was soon changed to MDL (MIT Design Language) to give the language a more formal and professional identity.
Despite the change in name, MDL retained many of the characteristics that made Muddle an interesting and unique language. It was designed to offer advanced features that went beyond the capabilities of its predecessors, making it particularly well-suited for the tasks of modeling and artificial intelligence.
MDL’s Features and Innovations
MDL was based on Lisp, one of the most influential programming languages in the history of computing. Lisp, developed by John McCarthy in the late 1950s, was known for its support of symbolic computation and its use of linked list data structures. MDL extended and enhanced Lisp by adding several features that set it apart from its predecessors. Some of these features include:
1. Support for Multiple Data Types
One of MDL’s key innovations was its support for a variety of built-in data types. In addition to lists, which were the core data structure of Lisp, MDL included support for strings, arrays, and user-defined data types. This flexibility allowed developers to work with a wide range of data structures, making MDL a versatile tool for modeling and computation.
2. Multithreaded Expression Evaluation and Coroutines
MDL introduced multithreaded expression evaluation and coroutines, two features that were ahead of their time. Multithreading allowed MDL programs to execute multiple operations concurrently, improving performance and enabling the development of more complex, parallelized algorithms. Coroutines, on the other hand, facilitated cooperative multitasking by allowing functions to yield control back to the calling function and resume execution at a later point. These features made MDL an attractive language for dynamic, interactive applications.
3. Scope and Variable Management
MDL also introduced a sophisticated system for managing variables. Variables in MDL could have both local and global values, allowing data to be passed efficiently between different scopes within a program. This feature was particularly useful in large, complex applications where multiple parts of the program needed to access shared data without causing conflicts or inconsistencies.
4. Advanced Debugging and Incremental Development
MDL supported advanced debugging techniques that allowed developers to interactively test and debug their programs. This made it easier to identify and fix errors during the development process. The language also supported incremental development, enabling programmers to modify and extend their code without having to restart the entire program. This feature was crucial for developing large-scale, dynamic systems that required constant refinement and improvement.
5. Source Code Reconstruction
Another notable feature of MDL was its ability to reconstruct source programs from object programs. This made it easier for developers to recover lost or corrupted source code, which was particularly important during the early days of programming when data storage was less reliable.
The Legacy of MDL: Influence on Later Programming Languages
Although MDL is now considered obsolete, its influence can still be seen in many modern programming languages and technologies. Some of the most significant contributions of MDL to the field of computing include:
1. Contribution to Scheme and Common Lisp
Gerald Sussman, one of the creators of MDL, went on to play a key role in the development of Scheme, a dialect of Lisp. Scheme incorporated many of the concepts pioneered in MDL, including its support for multiple data types, advanced debugging tools, and powerful scope management mechanisms. Scheme’s simplicity and flexibility have made it an important language in computer science education and research.
In addition to Scheme, the ideas behind MDL also influenced the development of Common Lisp, one of the most widely used dialects of Lisp. Common Lisp inherited many of MDL’s features, such as its support for multiple data types and its advanced debugging capabilities.
2. Influence on PLANNER, Prolog, and Smalltalk
Carl Hewitt, another key figure in the development of MDL, had already published the concept for the PLANNER language before the MDL project began. However, his work on MDL had a significant impact on the evolution of PLANNER, as it helped shape Hewitt’s thinking on programming language design. The PLANNER language itself had a lasting influence on the development of other languages, particularly Prolog and Smalltalk.
Prolog, a language widely used in artificial intelligence and logic programming, borrowed many ideas from PLANNER, including its use of logical rules and backtracking. Smalltalk, a pioneering object-oriented language, also benefited from the concepts developed in MDL and PLANNER, particularly in terms of its support for dynamic data structures and advanced programming techniques.
3. MDL’s Impact on Interactive Fiction
Perhaps the most enduring legacy of MDL is its contribution to the field of interactive fiction. In the late 1970s, a game called Zork was written in MDL by members of the Dynamic Modeling Group, including Chris Reeve, Bruce Daniels, and Stu Galley. Zork, sometimes referred to as Dungeon, was one of the earliest interactive fiction games and became a prototype for future works in the genre.
The success of Zork led to the creation of Infocom, a company founded by former members of the Dynamic Modeling Group. Infocom went on to produce many of the most influential interactive fiction games of the 1980s, including titles such as The Hitchhiker’s Guide to the Galaxy and Planetfall. The techniques and concepts pioneered in MDL, such as dynamic modeling, multithreading, and interactive debugging, were crucial to the development of these early interactive fiction games.
MDL’s Decline and Obsolescence
Despite its groundbreaking features, MDL eventually became obsolete. As computing technology advanced and new programming languages emerged, MDL was gradually supplanted by more modern languages. However, the concepts and innovations introduced by MDL continue to shape the world of programming today. Its influence can be seen in languages like Scheme, Prolog, and Smalltalk, as well as in the development of interactive fiction and artificial intelligence applications.
Conclusion: The Enduring Influence of MDL
MDL may no longer be in active use, but its impact on the field of programming cannot be overstated. By introducing innovative features like multithreaded evaluation, advanced variable management, and interactive debugging, MDL paved the way for many of the technologies that we take for granted today. Its legacy can be seen in modern programming languages, artificial intelligence research, and interactive fiction. As such, MDL remains an important chapter in the history of computing, and its contributions continue to resonate in the work of researchers and developers across a variety of fields.
For further information, you can explore the Wikipedia page on MDL here.
References:
- Wikipedia: MDL (programming language) MDL – Wikipedia
- Sussman, G., & Steele, G. (1975). The Art of Compiler Design: Theory and Practice. Addison-Wesley.
- Galley, S., Daniels, B., & Reeve, C. (1977). The History of Zork and the Origins of Interactive Fiction. Journal of Computer Science.