How to twist pointers without breaking them

Abstract

Using the theory of monoids and monoid actions, we give a unified framework that handles three common pointer manipulation tasks, namely, data serialisation, deserialisation, and memory allocation. Our main theoretical contribution is the formulation of the notion of a twisted functor, a generalisation of the semi-direct product construction for monoids. We show that semi-direct products and twisted functors are particularly well suited as an abstraction for many pointer manipulation tasks. We describe the implementation of these abstractions in the context of a cryptographic library for Haskell. Twisted functors allow us to abstract all pointer arithmetic and size calculations into a few lines of code, significantly reducing the opportunities for buffer overflows.