Functional MetaPost is a frontend to the MetaPost language
<http://www.tug.org/metapost.html> by John Hobby. Users
write their graphics as Haskell programs, which then emit
MetaPost code that can be compiled into encapsulated
PostScript files and smoothly included into e.g. LaTeX.

Your best bet for documentation are the German-language
documents

 * <http://cryp.to/funcmp/legacy-doc/Thesis.ps> and

 * <http://cryp.to/funcmp/legacy-doc/Tutorial.ps>;

or these (incomplete) English translations:

 * <http://cryp.to/funcmp/legacy-doc/Manual_eng.ps>,

 * <http://cryp.to/funcmp/legacy-doc/Thesis_eng.ps>,

 * <http://cryp.to/funcmp/legacy-doc/Tutorial_eng.ps>.