Macrodown is a markup language wrapping other markup languages such as TeX/LaTeX or HTML. It consists mainly of two “layers” ― the text layer and the program layer. The former is for writing documents in LaTeX-like syntax. The latter, which has ML-like syntax, is for defining functions and macros with Hindley-Milner polymorphic static typing. It enables you to write documents semantically markuped with flexible macros of your own making.