A Type System for Flexible User Interactions Handling

Engineering user interfaces involves the use of multiple user interactions. Developers may struggle with programming and using those user interactions because of a lack of flexibility that affects the current user interface programming approaches. First, developers may want to switch from one user interaction to another close one or combine multiple user interactions without changing much code. Second, developers may also want to use several user interactions to concisely produce the same user command. Third, developers may want to be warned about conflicts between involved user interactions. Currently, developers can hardly perform these first two cases without applying numerous code changes or producing boilerplate code. Regarding the third case, developers can only observe such issues during the execution of the interactive systems, which prolongs the detection time. To overcome these three issues this paper proposes a user interaction type system. This user interaction type system reifies user interactions as first-class concerns with typing facilities for enabling user interactions substitutability and union. It also allows the writing of type checking rules to check for possible issues related to user interactions at compile time. We implemented the type system within the TypeScript version of Interacto, a framework for processing user interactions. We evaluated the soundness and the expressiveness of our approach through several implemented use cases. This demonstrates the feasibility of the proposed approach and its ability to overcome the three mentioned issues.