To identify the source of runtime errors, techniques such as debug-by-execution are widely used, e.g., steppers. While this approach can also be useful for non-runtime errors, it has been less extensively explored due to the inherent difficulties in execution. In this NIER paper, we focus on debugging type errors in statically typed languages. We explore transformational debugging, a method that transforms erroneous code to provide users with an alternative perspective on the source code, thereby facilitating the debugging process.

Our approach consists of three phases: In the first phase, we use the error messages from the compiler’s type inferencer to ``freeze'' parts of the program. In the second phase, the type inferencer is used to reduce the number of frozen parts. In the third phase, a partial evaluator evaluates the partially frozen program. During partial evaluation, the frozen parts are treated as dynamic and, therefore, remain as code without being evaluated, while the other parts are treated as static and are evaluated.

This paper presents the generic algorithms for our debugging method, two heuristic strategies for the algorithms, and promising results using a prototype for a subset of OCaml. We explore a novel avenue for debugging: Transformational debugging and partial evaluation as helpful tools for debugging.