XE Design Rationale : Clu

XE is a programming language designed and implemented at the Helsinki University of Technology by the ExBed project. The design of XE is based on the CLU programming language. This paper discusses diierences between the two languages and the design decisions of XE. The XE language Arkk89] and its programming environment have been developed within the ExBed project, which was established to develop software tools for construction of embedded expert systems. The project needed a general purpose programming language with added facilities for rule-based programming. High level abstraction mechanisms and the possibility for eecient static semantic analysis were considered crucial for the language. The main reason for this was the wish to perform as much veriication and optimization as possible at compile time to satisfy the stringent requirements of embedded systems. There existed no programming language that satissed our needs and therefore we decided to design a new programming language. Our rst result, XC Nuut87], was based on C++ Stro86], and it was implemented using preprosessor techniques. We found out that the C++ approach had several major drawbacks Arkk88]. Also the preprocessor techniques could not give enough support for building a satisfactory programming environment.