Hazel Deriver: A Live Editor for Constructing Rule-Based Derivations

Students in programming languages and formal logic courses often struggle with constructing rule-based derivation trees due to the complexity of applying inference rules, the lack of immediate feedback, and the manual effort required for handwritten proofs. We present Hazel Deriver, a live, web-based editor designed to scaffold derivation construction through multiple layers of support. Built on the Hazel live programming environment, it provides a structured, interactive experience that encourages iterative exploration and real-time feedback. A preliminary user study with former students suggests that Hazel Deriver reduces the perceived difficulty of derivation tasks while improving conceptual understanding and engagement. We discuss the design of its layered scaffolding features and raise questions about balancing system guidance with learner autonomy.