Formalizing the debugging process in Haskell

Abstract

Due to its absence of side effects, it is usually claimed that reasoning about functional programs is simpler than reasoning about their imperative counterparts. Unfortunately, due to the absence of practical debuggers, finding bugs in lazy functional languages has been much more complex until quite recently. One of the easiest to use Haskell debuggers is Hood, whose behavior is based on the concept of observation of intermediate data structures. However, it can be hard to understand how it works when dealing with complex situations. In this paper, we introduce debugging facilities in the STG abstract machine. Our goal is to obtain debugging information as close to the one obtained by the Hood debugger as possible. By extending the STG abstract machine, we do not only provide a formal framework to the debugging process, but also an alternative method to implement debuggers. © Springer-Verlag Berlin Heidelberg 2005.