Run-time debugging for functional logic languages

This thesis describes the design, implementation and use of a run-time debugging tool for understanding the lazy semantics and locating failures in the functional logic language Curry. We provide a means for programmers to step in the evaluation order of program expressions at a source code level. Every expression evaluated is detected by a program coverage in a layout of the source code. Its run-time value can be represented to the user. The user can stop the execution of a program whenever he or she chooses to do so. A means to backward stepping is also provided. For large programs, we record only partial computations that are generated by evaluating selected expressions from the user. To achieve these means, we suggest and use some annotations in programs. Repre- sentation of intermediate steps of evaluations in a single-step mode is also provided by a distributed programming technique. Stepping in the real order of lazy evaluations could be helpful in searching for failures in simple programs and to beginners in understanding the behavior of functions in functional logic languages.