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Three Implementation Models for Scheme (1987) [pdf]

Posted: 2025-03-11 13:19:29

This 1987 paper by Dybvig explores three distinct implementation models for Scheme: compilation to machine code, abstract machine interpretation, and direct interpretation of source code. It argues that while compilation offers the best performance for finished programs, the flexibility and debugging capabilities of interpreters are crucial for interactive development environments. The paper details the trade-offs between these models, emphasizing the advantages of a mixed approach that leverages both compilation and interpretation techniques. It concludes that an ideal Scheme system would utilize compilation for optimized execution and interpretation for interactive use, debugging, and dynamic code loading, hinting at a system where the boundaries between compiled and interpreted code are blurred.

This 1987 paper by Dybvig, Hieb, and Bruggeman, titled "Three Implementation Models for Scheme," explores and contrasts three distinct models for implementing Scheme interpreters and compilers, aiming to illustrate the design space and trade-offs involved. These models, each representing a different point in the spectrum of implementation strategies, are termed the "Abstract Machine Model," the "Compiler Model," and the "Control Model." The authors delve into the strengths and weaknesses of each, considering factors such as performance, portability, debugging capabilities, and ease of implementation.

The Abstract Machine Model involves defining an abstract machine specifically designed for executing Scheme code. This abstract machine is characterized by a set of instructions tailored to Scheme's semantics, and an implementation consists of a virtual machine or interpreter for these instructions, often written in a lower-level language. This model offers a relatively straightforward implementation path and facilitates portability, as the interpreter can be implemented on various platforms. However, it can introduce performance overhead compared to compiled approaches due to the interpretation layer. The paper uses the Orbit compiler as an exemplary case of this model.

The Compiler Model focuses on directly translating Scheme code into native machine code for the target architecture. This approach prioritizes execution speed and leverages existing compiler technologies. The compiler performs various optimizations to generate efficient machine code, potentially resulting in significantly faster execution than interpreted approaches. However, this model can be more complex to implement due to the intricacies of code generation and optimization. Furthermore, portability is sacrificed as the compiler needs to be tailored for each target architecture. The paper references the Rabbit compiler as an example of this model, highlighting its focus on efficient code generation.

The Control Model takes a novel approach by representing Scheme programs as data structures that can be directly manipulated and evaluated by a core interpreter. This model emphasizes flexibility and dynamic behavior, particularly for features like continuations, which are challenging to implement efficiently in other models. Scheme programs are transformed into continuation-passing style (CPS), enabling sophisticated control flow manipulations. While this model provides elegance and powerful expressiveness, it can present performance challenges due to the overhead of representing and manipulating the control structures. The paper discusses the Chez Scheme system as an embodiment of the control model, illustrating its use of CPS and its focus on supporting advanced Scheme features efficiently.

The authors meticulously dissect each model, presenting their underlying mechanisms, advantages, and disadvantages. They provide insightful comparisons, emphasizing how each model addresses fundamental implementation challenges. The paper concludes by summarizing the key characteristics of each model and offering guidance on choosing the appropriate model based on specific project requirements and priorities. The overall contribution lies not in advocating for a single best approach, but rather in providing a comprehensive framework for understanding the trade-offs inherent in implementing a Scheme system, empowering developers to make informed design decisions.

Summary of Comments ( 4 )
https://news.ycombinator.com/item?id=43332143

HN commenters discuss the historical significance of the paper in establishing Scheme's minimalist design and portability. They highlight the cleverness of the three implementations, particularly the threaded code interpreter, and its influence on later languages like Lua. Some note the paper's accessibility and clarity, even for those unfamiliar with Scheme, while others reminisce about using the techniques described. A few comments delve into technical details like register allocation and garbage collection, comparing the approaches to modern techniques. The overall sentiment is one of appreciation for the paper's contribution to computer science and programming language design.

The Hacker News post linking to the 1987 paper "Three Implementation Models for Scheme" has generated a moderate number of comments, mostly focusing on the historical context of the paper and its significance in understanding Scheme implementations.

One commenter highlights the paper's importance for its clear explanation of the tradeoffs between different implementation strategies for Scheme, even today. They specifically mention how the paper's discussion of the "big picture" helps in understanding modern compiler discussions about register allocation and garbage collection.

Another comment points out the historical significance of the paper being published before the standardization of Scheme, resulting in the paper using a slightly different Scheme dialect. They also mention how the paper elegantly illustrates the common trade-offs in language implementation using a relatively small language like Scheme.

Several comments discuss the efficiency of various Scheme implementations and their approaches to compilation. One user mentions Indiana University's historical connection to Scheme and its compiler technology.

One comment delves deeper into the technical aspects, discussing how the paper's approach to environment representation is less relevant today due to advancements in generational garbage collection and precise stack maps. However, they acknowledge that the register allocation techniques discussed are still relevant.

Some users also shared anecdotal experiences about learning Scheme and using different implementations, highlighting personal connections to the historical context of the paper.

A few comments briefly touch upon the broader context of language design and implementation, comparing Scheme to other languages. One commenter notes the influence of the paper's authors on later work at Sun Microsystems related to Self and Java JIT compilers.

While the number of comments isn't extensive, they offer valuable insights into the historical relevance of the paper, its technical contributions, and its influence on subsequent developments in language implementation. The discussion largely revolves around appreciating the clarity and conciseness of the paper in explaining fundamental tradeoffs that remain relevant in contemporary compiler design.

Some Programming Language Ideas

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Posted: 2025-02-21 15:32:13

The author explores several programming language design ideas centered around improving developer experience and code clarity. They propose a system for automatically managing borrowed references with implicit borrowing and optional explicit lifetimes, aiming to simplify memory management. Additionally, they suggest enhancing type inference and allowing for more flexible function signatures by enabling optional and named arguments with default values, along with improved error messages for type mismatches. Finally, they discuss the possibility of incorporating traits similar to Rust but with a focus on runtime behavior and reflection, potentially enabling more dynamic code generation and introspection.

David Bos's blog post, "Some Programming Language Ideas," explores a collection of concepts he believes could enhance the design and functionality of programming languages. He prefaces his ideas by acknowledging that many have been explored before, but he feels they haven't gained the traction they deserve. His primary focus lies in improving the developer experience and enabling more expressive and powerful code.

A significant portion of the post is dedicated to the idea of structural typing combined with row polymorphism. Bos argues that this combination allows for greater flexibility and code reuse compared to nominal typing systems. He illustrates how structural typing permits functions to operate on any data structure that conforms to a specific shape or structure, irrespective of its declared type. Row polymorphism further enhances this by allowing functions to work with records that possess a minimum set of required fields while ignoring any additional fields. This allows for seamless extension of data structures without breaking existing code that interacts with them. He emphasizes the potential of this approach for simplifying code and promoting a more data-centric programming style.

Furthermore, Bos advocates for effects as data, proposing a system where side effects, such as file I/O or network operations, are explicitly represented as values within the language. This would allow for more precise control over when and how side effects occur, potentially simplifying concurrency and improving the testability of code. He outlines a scenario where effects are declared as part of a function's type signature, making the side effects of a function transparent to the caller.

The post also touches upon the concept of algebraic effects, suggesting they can provide a structured way to handle exceptions and other control flow mechanisms. This would allow developers to define custom effect handlers that determine how to respond to specific effects raised by functions. He briefly mentions the potential for combining algebraic effects with row polymorphism to achieve even greater expressiveness.

Additionally, Bos briefly explores the idea of integrating dependent types into programming languages, recognizing the complexities associated with implementing them effectively. He suggests that dependent types could enable stronger compile-time guarantees and improve the overall correctness of programs. He doesn't delve deeply into the specifics, acknowledging the ongoing research in this area.

Finally, he touches on compile-time function execution, expressing the desire for a language feature that permits running arbitrary code during compilation. This capability could be used for code generation, optimization, and other tasks traditionally performed by external build tools. He suggests that such a feature could streamline the development process and further enhance the power of the language. He concludes by reiterating his belief in the value of these ideas and their potential to shape the future of programming language design.

Summary of Comments ( 16 )
https://news.ycombinator.com/item?id=43128609

Hacker News users generally reacted positively to the author's programming language ideas. Several commenters appreciated the focus on simplicity and the exploration of alternative approaches to common language features. The discussion centered on the trade-offs between conciseness, readability, and performance. Some expressed skepticism about the practicality of certain proposals, particularly the elimination of loops and reliance on recursion, citing potential performance issues. Others questioned the proposed module system's reliance on global mutable state. Despite some reservations, the overall sentiment leaned towards encouragement and interest in seeing further development of these ideas. Several commenters suggested exploring existing languages like Factor and Joy, which share some similarities with the author's vision.

The Hacker News post titled "Some Programming Language Ideas" (https://news.ycombinator.com/item?id=43128609) has generated a modest number of comments, discussing various aspects of the proposed language features outlined in the linked article. While not a highly active discussion, several commenters engage with specific ideas, offering both praise and critique.

One commenter expresses appreciation for the author's exploration of alternative approaches to error handling, particularly the concept of "recoverable exceptions." They see potential in this approach for streamlining error management, suggesting it could lead to cleaner and more robust code.

Another commenter focuses on the proposed "algebraic subtyping" feature. While acknowledging its theoretical elegance, they raise concerns about the practical implications for language complexity and potential performance overhead. They question whether the benefits outweigh the added complexity for developers.

The discussion also touches upon the idea of integrating database concepts directly into the language. One commenter sees this as a promising direction, suggesting it could simplify data access and manipulation. However, another commenter expresses skepticism, arguing that it might lead to tight coupling between the language and specific database technologies, limiting flexibility.

A few comments delve into the specifics of syntax and semantics, debating the merits of different approaches. One commenter suggests an alternative syntax for a particular feature, aiming for improved readability. Another commenter raises a question about the semantics of a specific construct, seeking clarification from the author.

Overall, the comments reflect a thoughtful engagement with the proposed language ideas. While some commenters express enthusiasm for certain features, others raise valid concerns about complexity and practicality. The discussion highlights the trade-offs involved in language design and the importance of carefully considering the implications of new features. It does not, however, represent a large or particularly vibrant discussion thread.

I wrote my own “proper” programming language (2020)

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Posted: 2025-01-22 09:54:25

Mukul Rathi details his journey of creating a custom programming language, focusing on the compiler construction process. He explains the key stages involved, from lexing (converting source code into tokens) and parsing (creating an Abstract Syntax Tree) to code generation and optimization. Rathi uses his language, which he implements in OCaml, to illustrate these concepts, providing code examples and explanations of how each component works together to transform high-level code into executable machine instructions. He emphasizes the importance of understanding these foundational principles for anyone interested in building their own language or gaining a deeper appreciation for how programming languages function.

In a comprehensive blog post titled "I wrote my own “proper” programming language," author Mukul Rathi chronicles the journey of designing and implementing a programming language from its nascent conceptual stages to a functional, albeit rudimentary, state. He meticulously details the process of building a compiler, breaking down the complex task into manageable, discrete steps.

The post begins by outlining the fundamental architecture of a compiler, illustrating the typical workflow from source code to executable program. This includes lexical analysis, where the input code is tokenized; parsing, which involves constructing an Abstract Syntax Tree (AST) to represent the code's structure; semantic analysis, where type checking and other semantic rules are enforced; and finally, code generation, where the AST is translated into intermediate representations like bytecode or assembly language.

Rathi delves into the specifics of his implementation, utilizing Python as the language for his compiler. He elucidates the lexical analyzer’s role in categorizing individual components of the source code, such as keywords, identifiers, and operators, transforming the raw text into a stream of meaningful tokens. The parsing stage, he explains, involves organizing these tokens into a hierarchical tree structure – the AST – which reflects the grammatical relationships between different parts of the code. This is achieved using a recursive descent parsing technique.

Furthermore, the post underscores the importance of semantic analysis, which goes beyond mere syntax verification and delves into the meaning of the code. This crucial step involves ensuring type compatibility, checking for undeclared variables, and enforcing other language-specific semantic rules. Rathi describes how his compiler performs these checks, thereby ensuring the logical integrity of the program.

Finally, the post culminates in a discussion of code generation. While stopping short of generating machine code directly, Rathi explains how his compiler generates bytecode, a lower-level representation of the program. This bytecode can then be executed by a virtual machine, effectively bridging the gap between high-level source code and the underlying hardware. He emphasizes that while his compiler does not perform all the optimizations a production-ready compiler would, it demonstrates the essential steps involved in translating a high-level programming language into an executable format. The post concludes by acknowledging the project's limitations while highlighting its educational value as a practical exercise in compiler construction.

Summary of Comments ( 13 )
https://news.ycombinator.com/item?id=42791036

Hacker News users generally praised the article for its clarity and accessibility in explaining compiler construction. Several commenters appreciated the author's approach of building a complete, albeit simple, language instead of just a toy example. Some pointed out the project's similarity to the "Let's Build a Compiler" series, while others suggested alternative or supplementary resources like Crafting Interpreters and the LLVM tutorial. A few users discussed the tradeoffs between hand-written lexers/parsers and using parser generator tools, and the challenges of garbage collection implementation. One commenter shared their personal experience of writing a language and the surprising complexity of seemingly simple features.

The Hacker News thread for "I wrote my own “proper” programming language (2020)" contains several comments discussing various aspects of the linked article.

Many comments focus on tooling and alternative approaches to building a programming language. One user suggests using tools like Lex/Yacc or Flex/Bison for lexical analysis and parsing, offering a more robust and less error-prone method than manual implementation. This comment sparked a small discussion thread with another user pointing out that while powerful, these tools can add complexity, especially for beginners. They advocate for a simpler approach initially, recommending a hand-rolled recursive descent parser for its educational value in understanding the underlying mechanisms. This exchange highlights the trade-off between ease of implementation and the robustness of the final product.

Another commenter discusses the evolution of compiler construction and how techniques and tools have changed over time. They specifically mention the shift towards using LLVM as a backend for code generation and optimization. This offers the advantage of targeting multiple platforms without rewriting the backend for each one.

Several users commend the author of the article for undertaking such a complex project and sharing their knowledge. They praise the clear explanations and the step-by-step approach presented in the article, finding it accessible even for those without prior compiler development experience.

Some comments delve into specific aspects of the implementation, such as garbage collection, with one commenter suggesting exploring different garbage collection strategies. Another thread discusses the performance implications of different language design choices, emphasizing the importance of considering efficiency from the start.

One user expresses a common sentiment among language developers, mentioning the inherent difficulty and complexity involved in creating a "proper" programming language. They acknowledge the effort required for not just initial implementation, but also ongoing maintenance and improvement.

Finally, a few comments express interest in the language's potential applications and its future development. They inquire about specific features and express a desire to see the project evolve.

Show HN: Zyme – An Evolvable Programming Language

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Posted: 2024-11-15 14:13:19

Zyme is a new programming language designed for evolvability. It features a simple, homoiconic syntax and a small core language, making it easy to modify and extend. The language is designed to be used for genetic programming and other evolutionary computation techniques, allowing programs to be mutated and crossed over to generate new, potentially improved versions. Zyme is implemented in Rust and currently offers basic arithmetic, list manipulation, and conditional logic. It aims to provide a platform for exploring new ideas in program evolution and to facilitate the creation of self-modifying and adaptable software.

The Hacker News post introduces Zyme, a novel programming language designed with evolvability as its core principle. Zyme aims to facilitate the automatic creation and refinement of programs through evolutionary computation techniques, mimicking the process of natural selection. Instead of relying on traditional programming paradigms, Zyme utilizes a tree-based representation of code, where programs are structured as hierarchical expressions. This tree structure allows for easy manipulation and modification, making it suitable for evolutionary algorithms that operate by mutating and recombining code fragments.

The language itself is described as minimalistic, featuring a small set of primitive operations that can be combined to express complex computations. This minimalist approach reduces the search space for evolutionary algorithms, making the process of finding effective programs more efficient. The core primitives include arithmetic operations, conditional logic, and functions for manipulating the program's own tree structure, enabling self-modification. This latter feature is particularly important for evolvability, as it allows programs to adapt their own structure and behavior during the evolutionary process.

Zyme provides an interactive environment for experimentation and development. Users can define a desired behavior or task, and then employ evolutionary algorithms to automatically generate programs that exhibit that behavior. The fitness of a program is evaluated based on how well it matches the specified target behavior. Over successive generations, the population of programs evolves, with fitter individuals being more likely to reproduce and contribute to the next generation. This iterative process leads to the emergence of increasingly complex and sophisticated programs capable of solving the given task.

The post emphasizes Zyme's potential for exploring emergent behavior and solving complex problems in novel ways. By leveraging the power of evolution, Zyme offers a different approach to programming, shifting the focus from manual code creation to the design of evolutionary processes that can automatically discover efficient and effective solutions. The website includes examples and demonstrations of Zyme's capabilities, showcasing its ability to evolve programs for tasks like image processing and game playing. It also provides resources for learning the language and contributing to its development, suggesting a focus on community involvement in shaping Zyme's future.

Summary of Comments ( 23 )
https://news.ycombinator.com/item?id=42147110

HN commenters generally expressed skepticism about Zyme's practical applications. Several questioned the evolutionary approach's efficiency compared to traditional programming paradigms, particularly for complex tasks. Some doubted the ability of evolution to produce readable and maintainable code. Others pointed out the challenges in defining fitness functions and controlling the evolutionary process. A few commenters expressed interest in the project's potential, particularly for tasks where traditional approaches struggle, such as program synthesis or automatic bug fixing. However, the overall sentiment leaned towards cautious curiosity rather than enthusiastic endorsement, with many calling for more concrete examples and comparisons to established techniques.

The Hacker News post "Show HN: Zyme – An Evolvable Programming Language" sparked a discussion with several interesting comments.

Several commenters express interest in the project and its potential. One commenter mentions the connection to "Genetic Programming," acknowledging the long-standing interest in this field and Zyme's contribution to it. They also raise a question about Zyme's practical applications beyond theoretical exploration. Another commenter draws a parallel between Zyme and Wolfram Language, highlighting the shared concept of symbolic programming, but also questioning Zyme's unique contribution. This commenter seems intrigued but also cautious, prompting a need for clearer differentiation and practical examples. A different commenter focuses on the aspect of "evolvability" being central to genetic programming, subtly suggesting that the project description might benefit from emphasizing this aspect more prominently.

One commenter expresses skepticism about the feasibility of using genetic programming to solve complex problems, pointing out the challenges of defining effective fitness functions. They allude to the common issue in genetic programming where generated solutions might achieve high fitness scores in contrived examples but fail to generalize to real-world scenarios.

Furthering the discussion on practical applications, one commenter questions the current state of usability of Zyme for solving real-world problems. They express a desire to see concrete examples or success stories that would showcase the language's practical capabilities. This comment highlights a general interest in understanding how Zyme could be used beyond theoretical or academic contexts.

Another commenter requests clarification about how Zyme handles the issue of program bloat, a common problem in genetic programming where evolved programs can become excessively large and inefficient. This technical question demonstrates a deeper engagement with the technical aspects of Zyme and the challenges inherent in genetic programming.

Overall, the comments reveal a mix of curiosity, skepticism, and a desire for more concrete examples and clarification on Zyme's capabilities and differentiation. The commenters acknowledge the intriguing concept of an evolvable programming language, but also raise important questions about its practicality, usability, and potential to overcome the inherent challenges of genetic programming.

Stories with Tag programming language design

Three Implementation Models for Scheme (1987) [pdf]

Summary of Comments ( 4 ) https://news.ycombinator.com/item?id=43332143

Some Programming Language Ideas

Summary of Comments ( 16 ) https://news.ycombinator.com/item?id=43128609

I wrote my own “proper” programming language (2020)

Summary of Comments ( 13 ) https://news.ycombinator.com/item?id=42791036

Show HN: Zyme – An Evolvable Programming Language

Summary of Comments ( 23 ) https://news.ycombinator.com/item?id=42147110

Summary of Comments ( 4 )
https://news.ycombinator.com/item?id=43332143

Summary of Comments ( 16 )
https://news.ycombinator.com/item?id=43128609

Summary of Comments ( 13 )
https://news.ycombinator.com/item?id=42791036

Summary of Comments ( 23 )
https://news.ycombinator.com/item?id=42147110