Tactics for the Dafny Program Verifier

Many modern program verifiers are based on automated theorem provers, which enable full hiding of proof details and allow users to focus all their effort on the program text. This has the advantage that the additional expertise of theorem provers is not required, but has the drawback that when the prover fails to verify a valid program, the user has to annotate the program text with guidance for the verifier. This can be tedious, low-level and repetitive, and may impact on the annotation overhead, readability of the program text and overall development time. Inspired by proof tactics for interactive theorem provers , a notion of `tactics' for the state-of-the-art Dafny program verifier, called Tacny, is developed. With only minor extensions to the Dafny syntax, a user can encode high-level proof patterns as Dafny tactics, liberating herself from low-level and repetitive search tasks, whilst still working with familiar Dafny programming constructs. Manual search and guidance can be replaced with calls to such tactics, which will automate this task. We provide syntax and semantics for Tacny, and show feasibility through a prototype implementation, applied to several examples.