Enabling direct manipulation of plain-text output for template programs

Abstract

In modern software development, templates are widely used to generate artifacts, enhancing productivity and consistency. However, developers often face a tedious run-modify-run loop to verify template correctness, as outputs are only inspectable after execution. This issue is exacerbated when templates involve complex logic, highlighting the need for a solution that supports both artifact generation and user-friendly modifications. We propose BIT2, a framework enabling direct manipulation of plain-text output to modify template programs. A key challenge is that plain-text output lack structural information, making it difficult to map updates back to the template. BIT2 addresses this by generating computation-structured output, preserving the underlying logic, and supporting update operations (insertion, replacement, deletion) with carefully designed fusion semantics. Our implementation, written in TypeScript (18,000 lines of code), is available as an NPM module, complemented by a VSCode plugin, LiveT, for seamless template editing. Experimental results demonstrate that BIT2 achieves efficient evaluation and supports diverse update scenarios, significantly enhancing expressiveness in template development.