Stories with Tag formal languages

• From Languages to Language Sets

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  Posted: 2025-03-14 07:12:43

  Verbose tl;dr

  This post explores a shift in thinking about programming languages from individual entities to sets or families of languages. Instead of focusing on a single language's specific features, the author advocates for considering the shared characteristics and relationships between languages within a broader group. This approach involves recognizing core concepts and abstractions that transcend individual syntax, allowing for easier transfer of knowledge and the development of tools that can operate across multiple languages within a set. The author uses examples like the ML language family and the Lisp dialects to illustrate how shared underlying principles can unify seemingly disparate languages, leading to a more powerful and adaptable approach to programming.

  This blog post, titled "From Languages to Language Sets," delves into the intricacies of language server protocol (LSP) implementation and the challenges faced when attempting to support multiple programming languages concurrently within a single editor or Integrated Development Environment (IDE). The author meticulously outlines the progression of their thought process and the evolution of their approach to this multifaceted problem. They begin by describing the initial, naive approach of simply including distinct language servers for each individual language they desired to support. This straightforward method, while conceptually simple, quickly reveals its shortcomings due to the substantial resource consumption and performance overhead associated with running multiple servers simultaneously, particularly as the number of supported languages grows.

  The author then transitions to exploring a more sophisticated solution involving the development of a "language server multiplexer," or language set server. This server acts as a central intermediary, intelligently routing requests from the client (the editor or IDE) to the appropriate language server based on the context of the request, such as the file type or programming language being edited. This architectural shift brings about several advantages. First, it reduces the resource footprint by avoiding the need to run all language servers concurrently. Only the necessary servers are activated based on the active project or files being edited. Second, it simplifies the client-side implementation by providing a unified interface for interacting with multiple language servers. The client no longer needs to be aware of the individual servers or manage their lifecycle. Instead, it interacts solely with the multiplexer, which handles the complexities of server selection and communication.

  The post proceeds to elaborate on the implementation details of this multiplexer, explaining how it determines the correct language server to invoke based on the file extension and other relevant contextual information. The author carefully articulates the process of mapping file extensions to specific language servers and highlights the flexibility afforded by this approach. This adaptable mapping system allows for easy addition and removal of language support without requiring significant changes to the core architecture. Furthermore, the author discusses the nuances of handling requests for files with ambiguous or unsupported file extensions, ensuring graceful degradation of functionality in such scenarios.

  Finally, the post concludes by reflecting on the benefits and drawbacks of the proposed language set server approach. It reiterates the advantages of reduced resource consumption, simplified client-side integration, and improved maintainability. The author also acknowledges potential limitations, such as the added complexity of implementing and maintaining the multiplexer itself. However, they ultimately argue that the benefits outweigh the costs, particularly in scenarios where support for a wide array of programming languages is a critical requirement. The overall message underscores the importance of thoughtful architectural design when building complex systems like language servers and emphasizes the value of moving beyond simplistic solutions to achieve greater efficiency and scalability.

  • Programming Languages
  • language design
  • Set Theory
  • formal languages
  • language families
  • comparative linguistics
  • language classification
  • syntax
  • Semantics
  • parsing
  • language evolution
  • language features

  Summary of Comments ( 20 )
  https://news.ycombinator.com/item?id=43360287

  Verbose tl;dr

  The Hacker News comments discuss the concept of "language sets" introduced in the linked gist. Several commenters express skepticism about the practical value and novelty of the idea, questioning whether it genuinely offers advantages over existing programming paradigms like macros, polymorphism, or code generation. Some find the examples unconvincing and overly complex, suggesting simpler solutions could achieve the same results. Others point out potential performance implications and the added cognitive load of managing language sets. However, a few commenters express interest, seeing potential applications in areas like DSL design and metaprogramming, though they also acknowledge the need for further development and clearer examples to demonstrate its usefulness. Overall, the reception is mixed, with many unconvinced but a few intrigued by the possibilities.

  The Hacker News post "From Languages to Language Sets" sparks a discussion around the linked gist, which proposes the idea of "language sets" – combining multiple programming languages for different parts of a project based on their strengths. The comments section is moderately active, containing a mix of agreement, disagreement, and explorations of related concepts.

  Several commenters express enthusiasm for the idea, highlighting the potential benefits of using specialized languages for specific tasks. One commenter points out how this approach mirrors existing practices, such as using SQL for database interactions within a larger application written in a different language. They argue that explicitly recognizing and formalizing these "language sets" could lead to better tool development and more structured project organization. Another commenter emphasizes the productivity gains that could be achieved by choosing the right language for each job, rather than being constrained by a single language's limitations. They also suggest that improved tooling around language sets could simplify the process of integrating different languages.

  Others express skepticism or raise concerns. One commenter questions the novelty of the idea, suggesting that it simply describes the status quo of using multiple languages within a project. They argue that the term "language set" doesn't add much to the existing understanding of polyglot programming. Another commenter raises the issue of increased complexity when managing multiple languages, particularly regarding tooling, debugging, and team communication. They acknowledge the potential benefits but caution against overlooking the practical challenges.

  The discussion also delves into related topics. One commenter mentions the concept of "internal DSLs" (Domain-Specific Languages) and suggests that creating small, specialized languages within a larger project could be a more effective alternative to full-blown language sets. Another commenter draws parallels to the microservices architecture pattern, arguing that language sets could be seen as a similar approach applied to programming languages rather than services.

  Overall, the comments reflect a mixed reception to the idea of "language sets." While some see it as a valuable way to formalize and improve existing polyglot programming practices, others question its novelty and express concerns about increased complexity. The discussion also touches upon related concepts like internal DSLs and microservices, enriching the conversation around the central theme of choosing the right tools for the job.

• Fixing left and mutual recursions in grammars

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  Posted: 2025-02-02 08:31:12

  Verbose tl;dr

  The blog post details methods for eliminating left and mutual recursion in context-free grammars, crucial for parser construction. Left recursion, where a non-terminal derives itself as the leftmost symbol, is problematic for top-down parsers. The post demonstrates how to remove direct left recursion using factorization and substitution. It then explains how to handle indirect left recursion by ordering non-terminals and systematically applying the direct recursion removal technique. Finally, it addresses mutual recursion, where two or more non-terminals derive each other, converting it into direct left recursion, which can then be eliminated using the previously described methods. The post uses concrete examples to illustrate these transformations, making it easier to understand the process of converting a grammar into a parser-friendly form.

  This blog post, titled "Fixing left and mutual recursions in grammars," addresses the challenges posed by left and mutual recursion in context-free grammars, particularly during the process of top-down parsing. These types of recursion can cause infinite loops in recursive descent parsers, which try to expand a non-terminal by recursively calling the production rules. The post meticulously explains why these issues arise and provides solutions for resolving them.

  Left recursion occurs when a non-terminal immediately expands into a derivation that starts with itself. This creates a problem because the parser will endlessly attempt to expand the same non-terminal without consuming any input, leading to an infinite loop. The post illustrates this concept with a clear example of a grammar for arithmetic expressions. It then demonstrates a systematic method for eliminating left recursion by introducing new non-terminals and restructuring the grammar rules. This transformation effectively converts left-recursive productions into right-recursive ones. The resulting grammar is functionally equivalent to the original but is amenable to top-down parsing. The post carefully explains each step of this transformation, providing a general formula that can be applied to any left-recursive grammar. It emphasizes the importance of factoring out common prefixes to avoid unnecessary duplication in the rewritten grammar.

  Further, the post delves into mutual recursion, which arises when two or more non-terminals refer to each other in a cyclical manner. Similar to left recursion, this can cause infinite loops in recursive descent parsing. The post presents a comprehensive strategy for eliminating mutual recursion. This strategy involves selecting one of the mutually recursive non-terminals and substituting its productions into the other non-terminal's rules. This process effectively removes the direct mutual dependency, potentially creating left recursion in the process. The previously described method for eliminating left recursion is then applied to resolve any newly introduced left-recursive productions. The post uses a concrete example to demonstrate the steps involved in eliminating mutual recursion, again providing a clear and generalizable approach.

  Finally, the post briefly touches upon the role of tools like ANTLR and Yacc in handling left and mutual recursion. While these parser generators can handle direct left recursion, they generally do not handle indirect left recursion, underscoring the importance of understanding these concepts for grammar design. The post concludes by reiterating the benefits of understanding these techniques, particularly for building efficient and correct parsers.

  • grammar
  • Recursion
  • parsing
  • compiler design
  • Computer Science
  • Programming Languages
  • left recursion
  • mutual recursion
  • formal languages
  • syntax analysis

  Summary of Comments ( 20 )
  https://news.ycombinator.com/item?id=42907139

  Verbose tl;dr

  Hacker News users discussed the potential inefficiency of the presented left-recursion elimination algorithm, particularly its reliance on repeated string concatenation. They suggested alternative approaches using stacks or accumulating results in a list for better performance. Some commenters questioned the necessity of fully eliminating left recursion in all cases, pointing out that modern parsing techniques, like packrat parsing, can handle left-recursive grammars directly. The lack of formal proofs or performance comparisons with established methods was also noted. A few users discussed the benefits and drawbacks of different parsing libraries and techniques, including ANTLR and various parser combinator libraries.

  The Hacker News post titled "Fixing left and mutual recursions in grammars" sparked a brief but insightful discussion with a few key comments.

  One commenter questioned the practicality of the presented transformations, particularly for parsing, expressing concern that they seemed to prioritize generating strings from a grammar rather than the more common task of parsing a string into an abstract syntax tree. They pointed out that the transformations might complicate parsing by obscuring the original structure of the grammar. This commenter also hinted at a potential connection to the Pumping Lemma for context-free languages, suggesting it might be relevant to understanding the limitations of such transformations.

  Another comment offered an alternative approach to handling left recursion, suggesting the use of parsing techniques like packrat parsing or operator precedence parsing, which can handle left-recursive grammars directly without requiring transformations. This commenter argued these techniques offer a more practical solution for parsing in real-world scenarios. They further pointed out that the transformations presented in the article, while theoretically interesting, might not be the most efficient or straightforward way to deal with left recursion in practical parser implementations.

  A subsequent reply acknowledged the points made, conceding that the described transformations might not be universally applicable or optimal for all parsing situations. This reply clarified that the primary focus of the original post was on grammar manipulation and generation, rather than parsing specifically. It also admitted that for parsing, techniques like those mentioned (packrat parsing, operator precedence) are often more suitable. Finally, the reply suggested that the transformations might still be valuable in certain contexts beyond parsing, such as grammar analysis or transformation for other purposes.