Hacking Pandoc - jgm/pandoc GitHub Wiki
Complete pandoc consists of several distinct Haskell packages which you might need to look at:
To understand the pandoc implementation, besides Haskell
- understand how frontends and backends are joined in pandoc
- make yourself familiar with the Parsec monadic parser combinator library
- to get a grip on monads have a look at Haskell: Understanding_monads
See also:
Understanding code snippets - a q & a style explanation of code snippets from an Intermediate functional programmer trying to learn Haskell and how to structure a Haskell project.