Block-based programming systems employ a jigsaw metaphor to write programs. They are popular in the domain of programming education (e.g., Scratch), but also used as a programming interface for end-users in other disciplines, such as arts, robotics, and configuration management. In particular, block-based environments promise a convenient interface for Domain-Specific Languages (DSLs) for domain experts who might lack a traditional programming education. However, building a block-based environment for a DSL from scratch requires significant effort. This paper presents an approach to engineer block-based language interfaces by reusing existing language artifacts. We present Kogi, a tool for deriving block-based environments from context-free grammars. We identify and define the abstract structure for describing block-based environments. Kogi transforms a context-free grammar into this structure, which then generates a block-based environment based on Google Blockly. The approach is illustrated with four case studies, a DSL for state machines, Sonification Blocks (a DSL for sound synthesis), Pico (a simple programming language), and QL (a DSL for questionnaires). The results show that usable block-based environments can be derived from context-free grammars, and with an order of magnitude reduction in effort.

block-based environments, Blockly, DSLs, grammars, language workbenches, Rascal, syntax, visual languages
ACM SIGPLAN International Conference on Software Language Engineering
Centrum Wiskunde & Informatica, Amsterdam, The Netherlands

Verano Merino, M, & van der Storm, T. (2020). Block-based syntax from context-free grammars. In SLE 2020 - Proceedings of the 13th ACM SIGPLAN International Conference on Software Language Engineering, Co-located with SPLASH 2020 (pp. 283–295). doi:10.1145/3426425.3426948