For maximum modularity, you can combine this with functions like "zoom" and "magnify" of module Control.Lens.Zoom. They let you convert stateful operations that

For maximum modularity, you can combine this with functions like "zoom" and "magnify" of module Control.Lens.Zoom. They let you convert stateful operations that work on a fragment of the global state/environment into operations that work with the whole state/environment (provided that you have the appropriate lenses.) Very useful in complex monad stacks.