Shopify developed a new type inference algorithm called interprocedural sparse conditional type propagation (ISCTP) for their Ruby codebase. ISCTP significantly improves the performance of Sorbet, their gradual type checker, by more effectively propagating type information across method boundaries and within conditional branches. This addresses the common issue of "union types" exploding in complexity when analyzing code with many branching paths. By selectively tracking only relevant type refinements within each branch, ISCTP dramatically reduces the amount of computation required, resulting in faster type checking and fewer false positives. This improvement enables Shopify to scale their type checking efforts across their large and dynamic Ruby on Rails application.
The author recounts their experience debugging a perplexing issue with an inline eval() call within a JavaScript codebase. They discovered that an external library was unexpectedly modifying the global String.prototype, adding a custom method that clashed with the evaluated code. This interference caused silent failures within the eval(), leading to significant debugging challenges. Ultimately, they resolved the issue by isolating the eval() within a new function scope, effectively shielding it from the polluted global prototype. This experience highlights the potential dangers and unpredictable behavior that can arise when using eval() and relying on a pristine global environment, especially in larger projects with numerous dependencies.
The Hacker News comments discuss the practicality and security implications of the author's inline JavaScript evaluation solution. Several commenters express concern about the potential for XSS vulnerabilities, even with the author's implemented safeguards. Some suggest alternative approaches like using a dedicated sandbox environment or a parser that transforms the input into a safer format. Others debate the trade-offs between convenience and security, questioning whether the benefits of inline evaluation outweigh the risks. A few commenters appreciate the author's exploration of the topic and share their own experiences with similar challenges. The overall sentiment leans towards caution, with many emphasizing the importance of robust security measures when dealing with user-supplied code.
Niri is a new programming language designed for building distributed systems. It aims to simplify concurrent and parallel programming by introducing the concept of "isolated objects" which communicate via explicit message passing, eliminating shared mutable state and thus avoiding data races and other concurrency bugs. This approach, coupled with automatic memory management and a focus on performance, makes Niri suitable for developing robust and efficient distributed applications, potentially replacing complex actor models or other concurrency paradigms. The language is still under development, but shows promise for streamlining the creation of complex distributed systems.
Hacker News users discussed Niri's potential, focusing on its novel approach to UI design. Several commenters expressed excitement about the demo, praising its speed and the innovative concept of manipulating data directly within the interface. Concerns were raised about the practicality of text-based interaction for complex tasks and the potential learning curve. Some questioned the long-term viability of relying solely on a keyboard-driven interface, while others saw it as a powerful tool for experienced users. The discussion also touched upon comparisons to other tools like spreadsheets and the potential benefits for specific use cases like data analysis and programming. Some users expressed skepticism, finding the current implementation limited and wanting to see more concrete examples of its capabilities.
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.
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 blog post "It is not a compiler error (2017)" explores a subtle bug related to floating-point comparisons in C++. The author demonstrates how seemingly innocuous code, involving comparing a floating-point value against zero after decrementing it in a loop, can lead to unexpected infinite loops. This arises because floating-point numbers have limited precision, and repeated subtraction of a small value from a larger one might never exactly reach zero. The post emphasizes the importance of understanding floating-point limitations and suggests using alternative comparison methods, like checking if the value is within a small tolerance of zero (epsilon comparison), or restructuring the loop condition to avoid direct equality checks with floating-point numbers.
HN users discuss integer overflow in C/C++, focusing on its undefined behavior and the security implications. Some highlight the dangers, especially in situations where the compiler optimizes away overflow checks based on the assumption that it can't happen. Others point out that -fwrapv can enforce predictable wrapping behavior, making code safer but potentially slower. The discussion also touches on how static analyzers can help catch these issues, and the inherent difficulties in ensuring complete safety in C/C++ due to the language's flexibility. A few commenters mention alternatives like Rust, which offer stricter memory safety and overflow handling. One commenter shares a personal anecdote about an integer underflow vulnerability they found in a C++ program, emphasizing the real-world impact of these seemingly theoretical problems.
Modern compilers use sophisticated algorithms, primarily based on graph coloring, to determine register allocation. They construct an interference graph where nodes represent variables and edges connect variables that are live simultaneously. The compiler then tries to "color" the graph with a limited number of colors, representing available registers, such that no adjacent nodes share the same color. Variables that can't be assigned a color (register) are spilled to memory. Various optimizations, like live range analysis and coalescing, improve allocation efficiency by reducing the number of live variables and merging related variables. Ultimately, the compiler aims to minimize memory access and maximize register usage for frequently accessed variables, improving program performance.
Hacker News users discussed register allocation, focusing on its complexity and evolution. Several pointed out that modern compilers employ sophisticated algorithms like graph coloring for global register allocation, while others emphasized the importance of live range analysis. One commenter highlighted the impact of calling conventions and how they constrain register usage. The trade-offs between compile time and optimization level were also mentioned, with some noting that higher optimization levels often lead to better register allocation but longer compilation times. The difficulty of handling aliasing and the role of static single assignment (SSA) form in simplifying register allocation were also discussed.
This blog post explores a simplified variant of Generalized LR (GLR) parsing called "right-nulled" GLR. Instead of maintaining a graph-structured stack during parsing ambiguities, this technique uses a single stack and resolves conflicts by prioritizing reduce actions over shift actions. When a conflict occurs, the parser performs all possible reductions before attempting to shift. This approach sacrifices some of GLR's generality, as it cannot handle all types of grammars, but it significantly reduces the complexity and overhead associated with maintaining the graph-structured stack, leading to a faster and more memory-efficient parser. The post provides a conceptual overview, highlights the limitations compared to full GLR, and demonstrates the algorithm with a simple example.
Hacker News users discuss the practicality and efficiency of GLR parsing, particularly in comparison to other parsing techniques. Some commenters highlight its theoretical power and ability to handle ambiguous grammars, while acknowledging its potential performance overhead. Others question its suitability for real-world applications, suggesting that simpler methods like PEG or recursive descent parsers are often sufficient and more efficient. A few users mention specific use cases where GLR parsing shines, such as language servers and situations requiring robust error recovery. The overall sentiment leans towards appreciating GLR's theoretical elegance but expressing reservations about its widespread adoption due to perceived complexity and performance concerns. A recurring theme is the trade-off between parsing power and practical efficiency.
This paper demonstrates how seemingly harmless data races in C/C++ programs, specifically involving non-atomic operations on padding bytes, can lead to miscompilation by optimizing compilers. The authors show that compilers can exploit the assumption of data-race freedom to perform transformations that change program behavior when races are actually present. They provide concrete examples where races on padding bytes within structures cause compilers like GCC and Clang to generate incorrect code, leading to unexpected outputs or crashes. This highlights the subtle ways in which undefined behavior due to data races can manifest, even when the races appear to involve data irrelevant to program logic. Ultimately, the paper reinforces the importance of avoiding data races entirely, even those that might seem benign, to ensure predictable program behavior.
Hacker News users discussed the implications of Boehm's paper on benign data races. Several commenters pointed out the difficulty in truly defining "benign," as seemingly harmless races can lead to unexpected behavior in complex systems, especially with compiler optimizations. Some highlighted the importance of tools and methodologies to detect and prevent data races, even if deemed benign. One commenter questioned the practical applicability of the paper's proposed relaxed memory model, expressing concern that relying on "benign" races would make debugging significantly harder. Others focused on the performance implications, suggesting that allowing benign races could offer speed improvements but might not be worth the potential instability. The overall sentiment leans towards caution regarding the exploitation of benign data races, despite acknowledging the potential benefits.
This paper introduces Crusade, a formally verified translation from a subset of C to safe Rust. Crusade targets a memory-safe dialect of C, excluding features like arbitrary pointer arithmetic and casts. It leverages the Coq proof assistant to formally verify the translation's correctness, ensuring that the generated Rust code behaves identically to the original C, modulo non-determinism inherent in C. This rigorous approach aims to facilitate safe integration of legacy C code into Rust projects without sacrificing confidence in memory safety, a critical aspect of modern systems programming. The translation handles a substantial subset of C, including structs, unions, and functions, and demonstrates its practical applicability by successfully converting real-world C libraries.
HN commenters discuss the challenges and nuances of formally verifying the C to Rust transpiler, Cracked. Some express skepticism about the practicality of fully verifying such a complex tool, citing the potential for errors in the formal proofs themselves and the inherent difficulty of capturing all undefined C behavior. Others question the performance impact of the generated Rust code. However, many commend the project's ambition and see it as a significant step towards safer systems programming. The discussion also touches upon the trade-offs between a fully verified transpiler and a more pragmatic approach focusing on common C patterns, with some suggesting that prioritizing practical safety improvements could be more beneficial in the short term. There's also interest in the project's handling of concurrency and the potential for integrating Cracked with existing Rust tooling.
Summary of Comments ( 11 )
https://news.ycombinator.com/item?id=43353898
HN commenters generally expressed interest in Sorbet's type system and its performance improvements. Some questioned the practical impact of these optimizations for most users and the tradeoffs involved. One commenter highlighted the importance of constant propagation and the challenges of scaling static analysis, while another compared Sorbet's approach to similar features in other typed languages. There was also a discussion regarding the specifics of Sorbet's implementation, including its handling of runtime type checks and the implications for performance. A few users expressed curiosity about the "sparse" aspect and how it contributes to the overall efficiency of the system. Finally, one comment pointed out the potential for this optimization to significantly improve code analysis tools and IDE features.
The Hacker News post titled "Interprocedural Sparse Conditional Type Propagation" has generated several comments discussing the linked blog post about Sorbet's new type inference technique.
Several commenters express interest and appreciation for the technical depth of the article. One user describes the post as a "fascinating deep dive," praising the clear explanations and visualizations. They highlight the blog post's effectiveness in conveying the complexity of the problem and the ingenuity of the solution. Another commenter echoes this sentiment, emphasizing the rarity of such in-depth technical content and thanking the author for sharing their work.
A discussion unfolds around the trade-offs between performance and type checking accuracy. One user questions the performance implications of this new method, specifically asking about the overhead during static analysis. Another commenter speculates about the potential computational expense, pointing out the seeming complexity of the algorithms involved. The blog post author (presumably the same as the poster on Hacker News) then responds directly to these concerns, explaining that the performance impact has been surprisingly minimal in practice and providing some rationale for why this might be the case. They clarify that while the initial implementation was slower, subsequent optimizations have resulted in acceptable performance.
There's also a brief exchange about the applicability of these techniques to other type systems and languages. One user suggests potential parallels with similar analyses in other domains. However, the author clarifies that the specific method described is likely heavily tied to Sorbet's design and implementation, making direct adaptation to other type checkers challenging.
Finally, some comments delve into more specific technical aspects of the described method, such as the use of sparse representation and the handling of conditional types. One commenter asks a clarifying question about a specific detail in the algorithm, which again receives a direct response from the author.
Overall, the comments section indicates a positive reception of the blog post, with users appreciating the technical depth and clarity while also engaging in productive discussion about the practical implications and potential extensions of the presented ideas. The direct involvement of the author in addressing user questions and concerns adds significant value to the discussion.