pandoc-types- Types for representing a structured document

CopyrightCopyright (C) 2013 John MacFarlane
LicenseGNU GPL, version 2 or above
MaintainerJohn MacFarlane <>
Safe HaskellNone



Functions for manipulating Pandoc documents or extracting information from them by walking the Pandoc structure (or intermediate structures like '[Block]' or '[Inline]'. These are faster (by a factor of four or five) than the generic functions defined in Text.Pandoc.Generic.

Here's a simple example, defining a function that replaces all the level 3+ headers in a document with regular paragraphs in ALL CAPS:

import Text.Pandoc.Definition
import Text.Pandoc.Walk
import Data.Char (toUpper)

modHeader :: Block -> Block
modHeader (Header n _ xs) | n >= 3 = Para $ walk allCaps xs
modHeader x = x

allCaps :: Inline -> Inline
allCaps (Str xs) = Str $ map toUpper xs
allCaps x = x

changeHeaders :: Pandoc -> Pandoc
changeHeaders = walk modHeader

query can be used, for example, to compile a list of URLs linked to in a document:

extractURL :: Inline -> [String]
extractURL (Link _ (u,_)) = [u]
extractURL (Image _ (u,_)) = [u]
extractURL _ = []

extractURLs :: Pandoc -> [String]
extractURLs = query extractURL


class Walkable a b where


walk :: (a -> a) -> b -> b

walk f x walks the structure x (bottom up) and replaces every occurrence of an a with the result of applying f to it.

walkM :: (Monad m, Functor m) => (a -> m a) -> b -> m b

A monadic version of walk.

query :: Monoid c => (a -> c) -> b -> c

query f x walks the structure x (bottom up) and applies f to every a, appending the results.