Error Localization for Sequential Effect Systems (Extended Version)

TL;DR

This paper introduces a new method for precise error localization in sequential effect systems, improving the accuracy of runtime error reporting by leveraging residuals from ordered algebraic structures, and demonstrates its effectiveness in Java.

Contribution

It presents a novel approach using residuals for error localization in sequential effect systems, avoiding constraint solving and providing more accurate error reports.

Findings

Error locations are closer to actual failure points.

The approach works with existing effect quantales.

Implementation in Java shows improved error reporting.

Abstract

We describe a new concrete approach to giving predictable error locations for sequential (flow-sensitive) effect systems. Prior implementations of sequential effect systems rely on either computing a bottom-up effect and comparing it to a declaration (e.g., method annotation) or leaning on constraint-based type inference. These approaches do not necessarily report program locations that precisely indicate where a program may "go wrong" at runtime. Instead of relying on constraint solving, we draw on the notion of a residual from literature on ordered algebraic structures. Applying these to effect quantales (a large class of sequential effect systems) yields an implementation approach which accepts exactly the same program as an original effect quantale, but for effect-incorrect programs is guaranteed to fail type-checking with predictable error locations tied to evaluation order. We have implemented this idea in a generic effect system implementation framework for Java, and report on experiences applying effect systems from the literature and novel effect systems to Java programs. We find that the reported error locations with our technique are significantly closer to the program points that lead to failed effect checks.