This post explores the power and flexibility of Scheme macros for extending the language itself. It demonstrates how macros operate at the syntax level, manipulating code before evaluation, unlike functions which operate on values. The author illustrates this by building a simple infix macro that allows expressions to be written in infix notation, transforming them into the standard Scheme prefix notation. This example showcases how macros can introduce entirely new syntactic constructs, effectively extending the language's expressive power and enabling the creation of domain-specific languages or syntactic sugar for improved readability. The post emphasizes the difference between syntactic and procedural abstraction and highlights the unique capabilities of macros for metaprogramming and code generation.
Guy Steele's "Growing a Language" advocates for designing programming languages with extensibility in mind, enabling them to evolve gracefully over time. He argues against striving for a "perfect" initial design, instead favoring a core language with powerful mechanisms for growth, akin to biological evolution. These mechanisms include higher-order functions, allowing users to effectively extend the language themselves, and a flexible syntax capable of accommodating new constructs. Steele emphasizes the importance of "bottom-up" growth, where new features emerge from practical usage and are integrated into the language organically, rather than being imposed top-down by designers. This allows the language to adapt to unforeseen needs and remain relevant as the programming landscape changes.
Hacker News users discuss Guy Steele's "Growing a Language" lecture, focusing on its relevance even decades later. Several commenters praise Steele's insights into language design, particularly his emphasis on evolving languages organically rather than rigidly adhering to initial specifications. The concept of "worse is better" is highlighted, along with a discussion of how seemingly inferior initial designs can sometimes win out due to their adaptability and ease of implementation. The challenge of backward compatibility in evolving languages is also a key theme, with commenters noting the tension between maintaining existing code and incorporating new features. Steele's humor and engaging presentation style are also appreciated. One commenter links to a video of the lecture, while others lament that more modern programming languages haven't fully embraced the principles Steele advocates.
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.
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 blog post "Solving SICP" details the author's experience working through the challenging textbook Structure and Interpretation of Computer Programs (SICP). They emphasize the importance of perseverance and a deep engagement with the material, advocating against rushing through exercises or relying solely on online solutions. The author highlights the book's effectiveness in teaching fundamental computer science concepts through Scheme, and shares their personal approach of rewriting code multiple times and focusing on understanding the underlying principles rather than just achieving a working solution. Ultimately, they advocate for a deliberate and reflective learning process to truly grasp the profound insights SICP offers.
HN users discuss the blog post about working through SICP. Several commenters praise the book's impact on their thinking, even if they don't regularly use Scheme. Some suggest revisiting it after gaining more programming experience, noting a deeper appreciation for the concepts on subsequent readings. A few discuss the value of SICP's exercises in developing problem-solving skills, and the importance of actually working through them rather than just reading. One commenter highlights the significance of the book's metacircular evaluator chapter. Others debate the practicality of Scheme and the relevance of SICP's mathematical focus for modern programming, with some suggesting alternative learning resources.
The author is developing a Scheme implementation in async Rust to explore the synergy between the two. They believe Rust's robust tooling, performance, and memory safety, combined with its burgeoning async ecosystem, provide an ideal foundation for a modern Lisp dialect. Async capabilities offer exciting potential for concurrent Scheme programming, especially with features like lightweight tasks and channels. The project aims to leverage Rust's strengths while preserving the elegance and flexibility of Scheme, potentially offering a compelling alternative for both Lisp enthusiasts and Rust developers interested in functional programming.
HN commenters generally expressed interest in the project, finding the combination of Scheme and async Rust intriguing. Several questioned the choice of Rust for performance reasons, arguing that garbage collection makes it a poor fit for truly high-performance async workloads, and suggesting alternatives like C, C++, or even Zig. Some suggested exploring other approaches within the Rust ecosystem, like using a different garbage collector or a stack-allocated scheme. Others praised the project's focus on developer experience and the potential of combining Scheme's expressiveness with Rust's safety features. A few commenters also discussed the challenges of integrating garbage collection with async runtimes and the potential trade-offs involved. The author's responses clarified some of the design choices and acknowledged the performance concerns, indicating they're open to exploring different strategies.
A developer created a minimalist podcast player for iOS called Podcatcher, built using the Racket programming language. It supports basic features like subscribing to RSS feeds, downloading episodes, and background playback. The project aims to explore the viability of Racket for iOS development, focusing on a simple, functional app with a small footprint. The developer highlighted the challenges of working with Racket on iOS, including compilation times and integrating with native APIs, but ultimately found the experience positive and plans further development, including potential Android support.
HN users generally praised the developer's choice of Racket, expressing interest in its capabilities for iOS development. Some questioned the viability of Racket for mobile development, citing concerns about performance and community size compared to established options like Swift. A few users shared their own experiences with Racket and suggested improvements for the app, such as adding iPad support and offline playback. Several commenters expressed interest in trying the app or exploring the source code. The overall sentiment was one of curiosity and encouragement for the project.
Parinfer simplifies Lisp code editing by automatically managing parentheses, brackets, and indentation. It offers two modes: "Paren Mode," where indentation dictates structure and Parinfer adjusts parentheses accordingly, and "Indent Mode," where parentheses define the structure and Parinfer corrects indentation. This frees the user from manually tracking matching delimiters, allowing them to focus on the code's logic. Parinfer analyzes the code as you type, instantly propagating changes and offering immediate feedback about structural errors, leading to a more fluid and less error-prone coding experience. It's adaptable to different indentation styles and supports various Lisp dialects.
HN users generally praised Parinfer for making Lisp editing easier, especially for beginners. Several commenters shared positive experiences using it with Clojure, noting improvements in code readability and reduced parenthesis-related errors. Some highlighted its ability to infer parentheses placement based on indentation, simplifying structural editing. A few users discussed its potential applicability to other languages, and at least one pointed out its integration with popular editors. However, some expressed skepticism about its long-term benefits or preference for traditional Lisp editing approaches. A minor point of discussion revolved around the tool's name and how it relates to its functionality.
This blog post explores the powerful concept of functions as the fundamental building blocks of computation, drawing insights from the book Structure and Interpretation of Computer Programs (SICP) and David Beazley's work. It illustrates how even seemingly complex structures like objects and classes can be represented and implemented using functions, emphasizing the elegance and flexibility of this approach. The author demonstrates building a simple object system solely with functions, highlighting closures for managing state and higher-order functions for method dispatch. This functional perspective provides a deeper understanding of object-oriented programming and showcases the unifying power of functions in expressing diverse programming paradigms. By breaking down familiar concepts into their functional essence, the post encourages a more fundamental and adaptable approach to software design.
Hacker News users discuss the transformative experience of learning Scheme and SICP, particularly under David Beazley's tutelage. Several commenters emphasize the power of Beazley's teaching style, highlighting his ability to simplify complex concepts and make them engaging. Some found the author's surprise at the functional paradigm's elegance noteworthy, with one suggesting that other languages like Python and Javascript offer similar functional capabilities, perhaps underappreciated by the author. Others debated the benefits and drawbacks of "pure" functional programming, its practicality in real-world projects, and the learning curve associated with Scheme. A few users also shared their own positive experiences with SICP and its impact on their understanding of computer science fundamentals. The overall sentiment reflects an appreciation for the article's insights and the enduring relevance of SICP in shaping programmers' perspectives.
Summary of Comments ( 4 )
https://news.ycombinator.com/item?id=43892331
HN commenters largely praised the tutorial for its clarity and accessibility in explaining Scheme macros. Several appreciated the focus on hygienic macros and the use of simple, illustrative examples. Some pointed out the power and elegance of Scheme's macro system compared to other languages. One commenter highlighted the importance of understanding
syntax-rulesas a foundation before moving on to more complex macro systems likesyntax-case. Another suggested exploring Racket's macro system as a next step. There was also a brief discussion on the benefits and drawbacks of powerful macro systems, with some acknowledging the potential for abuse leading to unreadable code. A few commenters shared personal anecdotes of learning and using Scheme macros, reinforcing the author's points about their transformative power in programming.The Hacker News post "Extending a Language – Writing Powerful Macros in Scheme" (linking to a tutorial on Scheme macros) generated a moderate amount of discussion, with several commenters sharing their perspectives and experiences with macros and Lisp dialects.
One of the most compelling threads revolves around the practical applications and potential downsides of macros. A commenter points out the power of macros for creating embedded domain-specific languages (DSLs), citing examples like creating a small query language within a larger application. This sparked further discussion about the trade-offs between using macros for DSLs versus creating a separate external language, with considerations for debugging and the potential complexity introduced by macros.
Another commenter highlights the importance of hygiene in macros to prevent unintended variable capture and namespace collisions, a common pitfall for beginners. This leads to a brief discussion on the differences in hygienic macro systems between various Lisp dialects, specifically Scheme versus Common Lisp.
Several commenters reminisce about their experiences learning and using Lisp and macros, with some expressing appreciation for the elegance and power of the language, while others acknowledge the steep learning curve and potential for overuse of macros, leading to code that can be difficult to understand and maintain.
A few comments touch upon the differences between syntactic abstraction through macros and semantic abstraction. One commenter argues that while macros are powerful for syntactic manipulation, they don't inherently provide semantic abstraction, suggesting that other techniques, like higher-order functions, might be more suitable for certain tasks.
The tutorial's use of
syntax-caseis also mentioned, with a commenter noting its advantages over lower-level macro systems for its improved hygiene and pattern-matching capabilities.While there's no outright disagreement or controversy, the comments present a nuanced view of Scheme macros. They acknowledge the potential benefits for code generation, creating DSLs, and achieving syntactic abstraction, while also cautioning against overuse, potential complexity, and the importance of understanding hygiene. The comments generally encourage exploration of macros but emphasize the need for careful consideration and understanding of their implications.