Type engineering in OCaml, illustrated on the OCaml compiler

With four different kinds of variants and four different implementations of an object system, OCaml provides many options to design types to fit domain problems. However, it can be sometimes tempting to escalate type complexity, at the cost of code readability. It is therefore important to find a compromise between code complexity and type safety, in order to not let GADTs escape their scope. As a showcase, this talk proposes to review the use of advanced type features in the oldest OCaml project: the OCaml compiler