Guided Type Debugging

Abstract. We present guided type debugging as a new approach to quickly and reliably remove type errors from functional programs. The method works by gen-erating type-change suggestions that satisfy type specifications that are elicited from programmers during the debugging process. A key innovation is the incor-poration of target types into the type error debugging process. Whereas previous approaches have aimed exclusively at the removal of type errors and disregarded the resulting types, guided type debugging exploits user feedback about result types to achieve better type-change suggestions. Our method can also identify and remove errors in type annotations, which has been a problem for previous approaches. To efficiently implement our approach, we systematically generate all potential type changes and arrange them in a lattice structure that can be effi-ciently traversed when guided by target types that are provided by programmers