Slicing wxHaskell modules to derive the User Interface Abstract Model

In this paper, we discuss an experience slicing an Haskell program to separate its GUI developed with the graphic toolkit wxHaskell. The slicing operation was implemented in Strafunski, an Haskell-centered software bundle for generic programming and language processing. To analyze the user interface and extract the abstract model, we first parse the source Haskell program, and build its Abstract Syntax Tree (AST). Then a strategic traversal of the AST is used to slice the GUI wxHaskell code, and build the graph of dependencies between widgets. In this way it becomes possible to understand the execution flow of the program. Reusing and modifying legacy systems are complex and expensive tasks, because the required program comprehension is a difficult and time-consuming process. Thus, the need for methods and tools that facilitate program comprehension is urgent and strong. Reverse engineering aims at analyzing the software in order to represent it in an abstract format that makes easier to understand what it does and how it works. Reverse engineering tools provide means to support this task. Nowadays those software systems offer a rich interaction with the user, and their architectures are oriented towards a layered organization, separating at least the interface layer from the business core and data persistence modules. In this context—system maintenance and comprehension of software with graphical user interfaces—we present the results of a research work on the application of strategic programming and slicing techniques to the reverse engineering of interactive functional applications. Holmes, the tool so far developed and described in the paper, is capable of deriving the user interface abstract model for interactive functional programs. Since wxHaskell became the most famous graphic toolkit to build Graphical User Interfaces (GUI) for Haskell, we have investigated slicing techniques specialized for wxHaskell modules. In order to extract the user interface model from a Haskell/wxHaskell program we need to isolate the subset of functions responsible for the interaction. Slicing techniques are appropriate for that task. To build Holmes it is necessary to construct a slicing function [1, 2] that isolates the wxHaskell subprogram from the entire Haskell program. At a first glance, the obvious and easiest way is to define a recursive function to traverse the Abstract Syntax Tree (AST) of the program and return the wxHaskell subtree (maybe a forest). However, that approach forces the programmer to have full knowledge of Haskell grammar, and to write a complex and long set of mutually recursive