Adaptable Traces for Program Explanations

Program traces are a sound basis for explaining the dynamic behavior of programs. Alas, program traces can grow big very quickly, even for small programs, which diminishes their value as explanations. In this paper we demonstrate how the systematic simplification of traces can yield succinct program explanations. Specifically, we introduce operations for transforming traces that facilitate the abstraction of details. The operations are the basis of a query language for the definition of trace filters that can adapt and simplify traces in a variety of ways. The generation of traces is governed by a variant of Call-By-Value semantics which specifically supports parsimony in trace representations. We show that our semantics is a conservative extension of Call-By-Value that can produce smaller traces and that the evaluation traces preserve the explanatory content of proof trees at a much smaller footprint.