ppxderiving

ppx_deriving, commonly referred to as ppx_deriving, is a framework for the OCaml language that provides a collection of PPX derivers designed to automate boilerplate code for user-defined types. It aims to simplify common tasks such as comparing, printing, and serializing data by generating the corresponding functions at compile time.

Derivation is achieved by annotating type definitions with the deriving attribute. The standard syntax attaches a deriving clause to a type, for example: type t = { id : int; name : string } [@@deriving show, eq, ord]. When the OCaml compiler runs the PPX preprocessor, the ppx_deriving framework expands these annotations into actual OCaml code that implements the requested functionality. The approach keeps type definitions concise while maintaining type safety and readability.

ppx_deriving provides a core set of derivers such as show (pretty-printing), eq (equality), and ord (ordering). Many projects also rely on additional packages that provide derivers for serialization formats (for example JSON via Yojson) and binary formats, implemented through separate ppx_deriving-xxx packages that plug into the same mechanism. This modular design allows users to enable only the features they need.

Usage typically requires installing the ppx_deriving package and configuring the build system to apply the derivers, for example via OPAM and dune. While powerful, ppx_deriving may not derive every possible operation for all complex types, and in some cases manual implementation or custom derivers are necessary. It is a mature component of the OCaml ecosystem with ongoing maintenance and compatibility considerations across OCaml versions.