  This paper complements "Writing R Extensions," the official guide for writing
R extensions, for those interested in developing R packages using Rust. It
highlights idiosyncrasies of R and Rust that must be addressed by any
integration and describes how to develop Rust-based packages which comply with
the CRAN Repository Policy. This paper introduces the "cargo" framework, a
transparent Rust-based API which wraps commonly-used parts of R's API with
minimal overhead and allows a programmer to easily add additional wrappers.
