NAME

       Pandoc::Walker - utility functions to process Pandoc documents

SYNOPSIS

           use Pandoc::Walker;
           use Pandoc::Elements qw(pandoc_json);

           my $ast = pandoc_json(<>);

           # extract all links and image URLs
           my $links = query $ast, 'Link|Image' => sub { $_->url };

           # print all links and image URLs
           walk $ast, 'Link|Image' => sub { say $_->url };

           # remove all links
           transform $ast, sub {
               return ($_->name eq 'Link' ? [] : ());
           };

           # replace all links by their link text angle brackets
           use Pandoc::Elements 'Str';
           transform $ast, Link => sub {
               return (Str " < ", $_->content->[0], Str " > ");
           };

DESCRIPTION

       This module provides utility functions to traverse the abstract syntax tree (AST) of a
       pandoc document (see Pandoc::Elements for documentation of AST elements).

       Document elements are passed to action functions by reference, so don't shoot yourself in
       the foot by trying to directly modify the element.  Traversing a single element is not
       reliable neither, so put the element in an array reference if needed.  For instance to
       replace links in headers only by their link text content:

           transform $ast, Header => sub {
               transform [ $_[0] ], Link => sub { # make an array
                   return $_[0]->content;         # is an array
               };
           };

       See also Pandoc::Filter for an object oriented interface to transformations.

FUNCTIONS

   action ( [ $selector => ] $code [, @arguments ] )
   action ( { $selector => $code, ... } [, @arguments ] )
       Return an an action function to process document elements.

   walk( $ast, ... )
       Walks an abstract syntax tree and calls an action on every element or every element of
       given name(s). Additional arguments are also passed to the action.

       If and only if the action function returns "\undef" the current element is not traversed
       further.

       See also function "pandoc_walk" exported by Pandoc::Filter.

   query( $ast, ... )
       Walks an abstract syntax tree and applies one or multiple query functions to extract
       results.  The query function is expected to return a list or "\undef".  The combined query
       result is returned as array reference. For instance the "string" method of
       Pandoc::Elements is implemented as following:

           join '', @{
               query( $ast, {
                   'Str|Code|Math'   => sub { $_->content },
                   'LineBreak|Space' => sub { ' ' }
               } );

   transform( $ast, ... )
       Walks an abstract syntax tree and applies an action on every element, or every element of
       given name(s), to either keep it (if the action returns "undef" or "\undef"), remove it
       (if it returns an empty array reference), or replace it with one or more elements
       (returned by array reference or as single value).

       See also function "pandoc_filter" exported by Pandoc::Filter.

COPYRIGHT AND LICENSE

       Copyright 2014- Jakob Voss

       GNU General Public License, Version 2

       This module is heavily based on Pandoc by John MacFarlane.

SEE ALSO

       Haskell module Text.Pandoc.Walk <http://hackage.haskell.org/package/pandoc-
       types/docs/Text-Pandoc-Walk.html> for the original.