Local Reasoning for Global Properties

2 days ago

The author previously believed AI would not benefit from new programming languages, as AI can generate code in many existing languages.
However, AI often generates good local code (e.g., functions) but struggles with global program understanding, leading to unnecessary defensive checks that can cause exponential state complexity.
If AI's global reasoning weakness persists, programming language design may help by enforcing global properties through local reasoning, similar to Rust's data race prevention.
Rust's ownership types and Send/Sync traits prevent data races statically, allowing local reasoning to ensure global data-race freedom without a new sublanguage.
This demonstrates that programming languages can enforce surprising global properties (like data race freedom) with minimal burden on programmers.
AI-generated code often includes excessive defensive checks, which are unnecessary, hurt performance, and mislead about program states, causing exponential state explosions.
Future programming languages might incorporate features like effects systems to enforce more global properties, potentially benefiting AI code generation and human review.
While not all global properties can be enforced, there is evidence that usable languages can provide more guarantees, changing incentives for language design in the AI era.

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