Refining the Delta Debugging of Type Errors

Understanding the cause of a type error can be challenging; for over 30 years, researchers have proposed many sophisticated solutions that hardly made it into practice. Previously we presented a simple method for locating the cause of a type error in a functional program. Our method applies Zeller's isolating delta debugging algorithm, using the compiler as a black box: Simple line-based program slicing searches for a type error location. To improve speed, we incorporated a pre-processing stage for handling parse errors. In this paper, we note that the method needs refining. We introduce a new algorithm that replaces the previous pre-processing of parse errors with on-request handling. We implemented the algorithm and evaluated it for Haskell and OCaml programs to demonstrate that it is language agnostic.