Wikipedia: Camlp4. \url{http://en.wikipedia.org/wiki/Camlp4}, [doi]
Camlp4 is a software system for writing extensible parsers for programming languages. It provides a set of Objective Caml libraries that are used to define grammars as well as loadable syntax extensions of such grammars. Camlp4 stands for Caml Preprocessor and Pretty-Printer and one of its most important applications is the definition of domain-specific extensions of the syntax of OCaml.