Monads, zippers and views: virtualizing the monad stack

Abstract

We make monadic components more reusable and robust to changes by employing two new techniques for virtualizing the monad stack: the monad zipper and monad views. The monad zipper is a higher-order monad transformer that creates virtual monad stacks by ignoring particular layers in a concrete stack. Monad views provide a general framework for monad stack virtualization: they take the monad zipper one step further and integrate it with a wide range of other virtualizations. For instance, particular views allow restricted access to monads in the stack. Furthermore, monad views provide components with a call-by-reference-like mechanism for accessing particular layers of the monad stack.