Causality Error Tracing in HipHop.js

HipHop.js is a synchronous reactive DSL for JavaScript built on top of Hop.js. HipHop.js follows the model of perfect synchrony introduced in the Esterel programming language, this may lead to classical causality error cycles, which might be difficult to isolate and to fix. In this work, we discuss in detail the support for debugging causality errors in HipHop.js. First, we provide illustrative examples explaining the origin and formation of causality errors and the difficulties faced in debugging them. Then, we present the techniques and algorithms used to construct precise error messages that direct programmers to the source of errors. We illustrate the effectiveness of the proposed methods on a real world example. Recent reactive technologies and programming languages like FRP, ReactiveX, etc., used in game and GUI development too encounter causality errors, and we feel that our approach used in HipHop.js can help them in debugging in a better way.