Developed monadic folding utilities, scanlM and scanrM, for the leanprover-community/batteries repository, enabling effectful list folds within Lean’s functional programming paradigm. The implementation focused on modularity and composability, allowing downstream projects to perform monadic computations more safely and cleanly. This work centered on collaborative development, adhering to contributor guidelines and integrating feedback from co-authors. By expanding the library’s functional capabilities, the contribution streamlined the composition of monadic effects and improved support for asynchronous workflows. The project demonstrated proficiency in Lean, functional programming concepts, and incremental feature delivery within a multi-repository ecosystem, with an emphasis on code quality and maintainability.