Verifying Fail-Free Declarative Programs

by Michael Hanus

Proc. of the 20th International Symposium on Principles and Practice of Declarative Programming (PPDP 2018), ACM Press, pp. 12:1-12:13, 2018
© ACM Press

Failed computations are a frequent problem in software system development. Some failures have external reasons (e.g., missing files) that can be caught by exception handlers. Many other failures have internal reasons, such as calling a partially defined operation with unintended arguments. In order to avoid the latter kind of failures, one can try to analyze the program at compile time for potential occurrences of these failures at run time. In this paper we present an approach to verify the absence of such failures in functional logic programs. Since programming with failures is a typical technique in logic programming, we are not interested to abandon partially defined operations at all. Instead, we want to verify conditions which ensure that operations can be executed without running into a failure. For this purpose, we propose to annotate operations with non-fail conditions that are verified at compile time with an SMT solver. For successfully verified programs, it is ensured that computations never fail provided that the non-fail condition of the main operation is satisfied.

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