Abstraction and Genericity in Why3

Abstract

The benefits of modularity in programming—abstraction barriers, which allow hiding implementation details behind an opaque interface, and genericity, which allows specializing a single implementation to a variety of underlying data types—apply just as well to deductive program verification, with the additional advantage of helping the automated proof search procedures by reducing the size and complexity of the premises and by instantiating and reusing once-proved properties in a variety of contexts In this paper, we demonstrate the modularity features of WhyML, the language of the program verification tool Why3. Instead of separating abstract interfaces and fully elaborated implementations, WhyML uses a single concept of module, a collection of abstract and concrete declarations, and a basic operation of cloning which instantiates a module with respect to a given partial substitution, while verifying its soundness. This mechanism brings into WhyML both abstraction and genericity, which we illustrate on a small verified Bloom filter implementation, translated into executable idiomatic C code.