In this presentation, we intend to show a state-of-the-art DSL implementation in OCaml, with concrete examples and experience reports.

In particular, we found that some advanced practices, while accepted among the hardcore OCaml developers (e.g. use of row type variables through object types), lacked visibility and documentation: some of them deserve to be better known.

Our experience is based on the Catala compiler, a DSL for the implementation of algorithms defined in law.