Abstract

The \size-change termination" principle for a rst-order functional language with well-founded data is: a program terminates on all inputs if every innite call sequence (following program control ow) would cause an innite descent in some data values. Size-change analysis is based only on local approximations to parameter size changes derivable from program syntax. The set of innite call sequences that follow program ow and can be recognized as causing innite descent is an !-regular set, representable by a Buchi automaton. Algorithms for such automata can be used to decide size-change termination. We also give a direct algorithm operating on \size-change graphs" (without the passage to automata). Compared to other results in the literature, termination analysis based on the size-change principle is surprisingly simple and general: lexical orders (also called lexicographic orders), indirect function calls and permuted arguments (descent that is not in-situ) are all handled auto...

Citations