A Practical Tutorial for FermaT and WSL Transformations

Software evolution is mainly about how program code changes in its environment. A very important part of these changes is the re-engineering of software that can be done very efficiently and more importantly reliably by using tools that offer formally provable transformations. FermaT is the current implementation of the language WSL (short for Wide Spectrum Language) and the surrounding code transformation libraries. It is available under the GPL v3 software licence and works on most computer platforms, including Linux, Windows and Mac OS. Early versions of this tool were developed as “The Maintainer’s assistant”[Ward 1989] and it has been developed and reimplemented since then. It has been used in several industrial projects of converting legacy assembly code to human understandable and maintainable C and COBOL[Ward 1999][Ward 2004][Ward et al. 2004][Ward 2013]. It also has support for program slicing[Ward and Zedan 2017] and can be used to derive program code from abstract specifications[Ward and Zedan 2014]. A companion graphical application FermaT Maintenance Environment (FME)[Ladkau 2007] is also available and can be very useful especially for initial experiment with the transformation system. This tutorial will give just a brief overview of WSL and some of the needed ideas and will not go into depths with the syntax of the language that is available in the official manual[Ward et al. 2008]. This paper is organised as follows: Section 2 shows some aspects of FermaT and how to use it and expand it, mainly through the expression and condition simplifiers (Section 2.1. A working example is introduced in Section 2.2, which is then developed into a full transformation that can be added to the system in Section 2.3. Finally Section 3 gives a brief conclusion to the paper. Along the way Some