Declarative Debugging Meets the World

Declarative debugging has been proposed as a suitable technique for diagnosing errors. It is particularly attractive for declarative programming languages, whose operational semantics differs substantially from their declarative semantics. Declarative debuggers are usually described and implemented by means of a program transformation. However, this transformation does not mix well with monadic I/O, which is used by lazy functional and functional logic languages. Therefore, declarative debuggers for such languages either do not support debugging of programs involving stateful computations at all, or require special support from the compiler and its runtime system. In this paper, we present a modified program transformation that blends nicely with monadic I/O and therefore covers the whole language without additional support from the target implementation.