This is the year 2008 and ML-style exceptions are everywhere. Most modern languages, whether academic or industrial, feature some variant of this mechanism. Languages such as Java even feature static coverage-checking for such exceptions, something not available for ML languages, at least not without resorting to external tools.
In this document, we demonstrate a design principle and a tiny library for managing errors in a functional manner, with static coverage-checking, automatically-inferred, structurally typed and hierarchical exceptional cases, with a reasonable run-time penalty. Our work is based on OCaml and features monads, polymorphic variants, compile-time code rewriting and trace elements of black magic.