Decomposable Type Highlighting for Bidirectional Type and Cast System

2026-07-15

AI Summary

Debugging static and dynamic type errors is often hindered by the lack of intuitive explanations of type inference and coercion processes. This work proposes a decomposable type highlighting mechanism, integrated for the first time into a bidirectional type system coupled with a dynamic type coercion framework, to interactively visualize type inference paths and dynamic conversion behaviors in real time through a dedicated interface. A prototype implementation in the Hazel language demonstrates the effectiveness of this approach, significantly improving developers’ ability to understand and diagnose mixed-type errors. The proposed method establishes a novel paradigm for type-level debugging, offering enhanced transparency and interactivity in reasoning about type-related program behavior.

Abstract

We explore how to provide programmers with an interactive interface for explaining the process by which static types and dynamic casts are derived, with the goal of improving the debugging of static and dynamic type errors. To this end, we define mathematical foundations for a decomposable highlighting system within a bidirectional system and show how these can be propagated through dynamic types in a cast system. Our prototype implementation in the gradually typed Hazel language includes a web-based user interface, through which we highlight the importance of type-level debugging.

Problem

• type debugging
• interactive interface
• static types
• dynamic casts
• bidirectional type system

Innovation

• decomposable highlighting
• bidirectional type system
• dynamic casts
• gradual typing
• type-level debugging