Text.Pandoc.Walk

pandoc-types-1.16.0.1: Types for representing a structured document

Copyright | Copyright (C) 2013 John MacFarlane
License | GNU GPL, version 2 or above
Maintainer | John MacFarlane <jgm@berkeley.edu>
Stability | alpha
Portability | portable
Safe Haskell | None
Language | Haskell98

Text.Pandoc.Walk

Description

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

# Documentation

class Walkable a b where

Methods

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.

Instances

Walkable Inline Citation |
Walkable Inline Inline |
Walkable Inline Block |
Walkable Inline MetaValue |
Walkable Inline Meta |
Walkable Inline Pandoc |
Walkable Block Citation |
Walkable Block Inline |
Walkable Block Block |
Walkable Block MetaValue |
Walkable Block Meta |
Walkable Block Pandoc |
Walkable Meta Meta |
Walkable Pandoc Pandoc |
(Foldable t, Traversable t, Walkable a b) => Walkable a (t b) |
(Walkable a b, Walkable a c) => Walkable a (b, c) |