Complete and partial redex trails of functional computations

Redex trails are histories of functional computations by graph reduction; their main application is fault-tracing. A prototype implementation of a tracer based on redex trails [8] demonstrated the promise of the technique, but was limited in two respects: (1) trails did not record every reduction, only those constructing a new value; (2) even so computing trails was very expensive, particularly in terms of the memory space they occupied. In this paper, we address both problems: complete redex trails provide a full computational record; partial versions of these trails exclude all but selected details, greatly reducing memory costs. We include results of experiments tracing several applications, including a compiler.