VeriFly: On-the-fly Assertion Checking via Incrementality

Abstract

Assertion checking is an invaluable programmer’s tool for finding many classes of errors or verifying their absence in dynamic languages such as Prolog. For Prolog programmers, this means being able to have relevant properties, such as modes, types, determinacy, nonfailure, sharing, constraints, and cost, checked and errors flagged without having to actually run the program. Such global static analysis tools are arguably most useful the earlier they are used in the software development cycle, and fast response times are essential for interactive use. Triggering a full and precise semantic analysis of a software project every time a change is made can be prohibitively expensive. This is specially the case when complex properties need to be inferred for large, realistic code bases. In our static analysis and verification framework, this challenge is addressed through a combination of modular and incremental (context- and path-sensitive) analysis that is responsive to program edits, at different levels of granularity. In this tool paper, we present how the combination of this framework within an integrated development environment (IDE) takes advantage of such incrementality to achieve a high level of reactivity when reflecting analysis and verification results back as colorings and tooltips directly on the program text – the tool’s VeriFly mode. The concrete implementation that we describe is Emacs-based and reuses in part off-the-shelf “on-the-fly” syntax checking facilities (flycheck). We believe that similar extensions are also reproducible with low effort in other mature development environments. Our initial experience with the tool shows quite promising results, with low latency times that provide early, continuous, and precise assertion checking and other semantic feedback to programmers during the development process. The tool supports Prolog natively, as well as other languages by semantic transformation into Horn clauses.

Fifty Years of Prolog and Beyond

“…Section 2.10.2). CiaoPP then is capable of finding nontrivial bugs statically or dynamically and can statically verify that the program complies with the specifications, even interactively (Sanchez-Ordaz et al . 2021).…”

“…The combination of static and dynamic verification, debugging, and testing of Ciao is relevant here (Hermenegildo et al . 2005;Sanchez-Ordaz et al . 2021).…”

Fifty Years of Prolog and Beyond

“…Section 2.9.2). CiaoPP then is capable of finding non-trivial bugs statically or dynamically, and can statically verify that the program complies with the specifications, even interactively (Sanchez-Ordaz et al, 2021). The Ciao model can be considered an antecedent of the now-popular gradual-and hybrid-typing approaches (Flanagan, 2006;Siek and Taha, 2006;Rastogi et al, 2015).…”

“…• Increased capabilities in debuggers (e.g., constraint debugging or graphical interaction), performance profiling tools, and testing frameworks. The combination of static and dynamic verification, debugging, and testing of Ciao is relevant here (Hermenegildo et al, 2005;Sanchez-Ordaz et al, 2021). • Better experience using interactive shells: Prolog could also profit from being integrated within notebooks such as Jupyter, as has been done in SWISH (Wielemaker et al, 2019).…”