Developing GUI Applications in a Verified Setting

Abstract

Although there have been major achievements in verified software, work on verifying graphical user interfaces (GUI) applications is underdeveloped relative to their ubiquity and societal importance. In this paper, we present a library for the development of verified, statedependent GUI applications in the dependently typed programming language Agda. The library uses Agda's expressive type system to ensure that the GUI, its controller, and the underlying model are all consistent, significantly reducing the scope for GUI-related bugs. We provide a way to specify and prove correctness properties of GUI applications in terms of user interactions and state transitions. Critically, GUI applications and correctness properties are not restricted to finite state machines and may involve the execution of arbitrary interactive programs. Additionally, the library connects to a standard, imperative GUI framework, enabling the development of native GUI applications with expected features, such as concurrency. We present applications of our library to building GUI applications to manage healthcare processes. The correctness properties we consider are the following: (1) That a state can only be reached by passing through a particular intermediate state, for example, that a particular treatment can only be reached after having conducted an X-Ray. (2) That one eventually reaches a particular state, for example, that one eventually decides on a treatment. The specification of such properties is defined in terms of a GUI application simulator, which simulates all possible sequences of interactions carried out by the user.

Declarative GUIs

“…The library presented in this paper uses a custom-built backend based on SDL and Rasterific, as described in Section 3.4. We have also developed an alternative version of this library based on the standard wxWidgets toolkit via wx-Haskell [80], which is described in previous work [7]. There are several tradeoffs between the two versions of the library.…”

“…However, wxWidgets integrates better with the host operating system and has a larger selection of components that can be integrated with our approach without too much additional effort. The library described in [7] is also more generic in that it supports nested frames and modifying properties without redrawing the entire GUI. An advantage of the simpler version presented here is that it is easier to programmatically generate GUI applications from higher-level declarative specifications, as illustrated by the translation of business processes into GUIs in Sections 5.2 and 5.3.…”

“…An advantage of the simpler version presented here is that it is easier to programmatically generate GUI applications from higher-level declarative specifications, as illustrated by the translation of business processes into GUIs in Sections 5.2 and 5.3. Due to the increased complexity, the application presented in [7] is much simpler than the case study presented here.…”