Goanna: a novel approach for automated type error debugging

Abstract Statically typed languages offer many advantages in software engineering, including bug prevention, enhanced code quality, and reduced maintenance costs. However, these benefits come at the expense of a steep learning curve and a slower development pace. Although known for its expressive and strong type system, Haskell often frustrates programmers as they learn and use that type system, especially when debugging type errors. We introduce Goanna, a novel type checker for Haskell that focuses on improving error diagnostics. When a type error occurs, Goanna identifies a comprehensive list of possible causes and provides a potential course of action for each. To achieve this, Goanna uses constraint logic programming and Minimal Correction Subsets (MCSes) to support its diagnostics. We evaluated Goanna’s effectiveness on 49,750 Haskell programs, demonstrating its ability to identify root causes with higher accuracy (81.6%) than traditional tools (Helium, 65.5%; GHC, 33.7%). In our benchmark study, Goanna shows performance constraints when diagnosing large programs containing complex errors, but remains responsive enough to provide real-time debugging assistance for small to medium-sized programs.