Developed principled Alternative-based monad support for the leanprover-community/batteries repository, focusing on formalizing the semantics of failure and orElse within monads equipped with Alternative. Introduced the AlternativeMonad and LawfulAlternative classes to rigorously define these behaviors, ensuring correctness and predictability in alternative-based composition. Provided comprehensive instances for Option, OptionT, StateT, ReaderT, and StateRefT', enabling safe and consistent optional and effectful computations across common monad transformer stacks. Leveraged expertise in Lean, functional programming, and monad transformers to enhance the reliability of effectful code, with an emphasis on type theory and formal law-driven design for robust abstraction boundaries.