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.\" ========================================================================
.\"
.IX Title "Pandoc::Walker 3pm"
.TH Pandoc::Walker 3pm "2017-03-31" "perl v5.24.1" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
Pandoc::Walker \- utility functions to process Pandoc documents
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&    use Pandoc::Walker;
\&    use Pandoc::Elements qw(pandoc_json);
\&
\&    my $ast = pandoc_json(<>);
\&
\&    # extract all links and image URLs
\&    my $links = query $ast, \*(AqLink|Image\*(Aq => sub { $_\->url };
\&
\&    # print all links and image URLs
\&    walk $ast, \*(AqLink|Image\*(Aq => sub { say $_\->url };
\&
\&    # remove all links
\&    transform $ast, sub {
\&        return ($_\->name eq \*(AqLink\*(Aq ? [] : ());
\&    };
\&
\&    # replace all links by their link text angle brackets
\&    use Pandoc::Elements \*(AqStr\*(Aq;
\&    transform $ast, Link => sub {
\&        return (Str " < ", $_\->content\->[0], Str " > ");
\&    };
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module provides utility functions to traverse the abstract syntax tree
(\s-1AST\s0) of a pandoc document (see Pandoc::Elements for documentation of \s-1AST\s0
elements).
.PP
Document elements are passed to action functions by reference, so \fIdon't
shoot yourself in the foot\fR 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:
.PP
.Vb 5
\&    transform $ast, Header => sub {
\&        transform [ $_[0] ], Link => sub { # make an array
\&            return $_[0]\->content;         # is an array
\&        };
\&    };
.Ve
.PP
See also Pandoc::Filter for an object oriented interface to transformations.
.SH "FUNCTIONS"
.IX Header "FUNCTIONS"
.ie n .SS "action ( [ $selector => ] $code [, @arguments ] )"
.el .SS "action ( [ \f(CW$selector\fP => ] \f(CW$code\fP [, \f(CW@arguments\fP ] )"
.IX Subsection "action ( [ $selector => ] $code [, @arguments ] )"
.ie n .SS "action ( { $selector => $code, ... } [, @arguments ] )"
.el .SS "action ( { \f(CW$selector\fP => \f(CW$code\fP, ... } [, \f(CW@arguments\fP ] )"
.IX Subsection "action ( { $selector => $code, ... } [, @arguments ] )"
Return an an action function to process document elements.
.ie n .SS "walk( $ast, ... )"
.el .SS "walk( \f(CW$ast\fP, ... )"
.IX Subsection "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.
.PP
If and only if the action function returns \f(CW\*(C`\eundef\*(C'\fR the current element is
not traversed further.
.PP
See also function \f(CW\*(C`pandoc_walk\*(C'\fR exported by Pandoc::Filter.
.ie n .SS "query( $ast, ... )"
.el .SS "query( \f(CW$ast\fP, ... )"
.IX Subsection "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 \f(CW\*(C`\eundef\*(C'\fR.
The combined query result is returned as array reference. For instance the
\&\f(CW\*(C`string\*(C'\fR method of Pandoc::Elements is implemented as following:
.PP
.Vb 5
\&    join \*(Aq\*(Aq, @{
\&        query( $ast, {
\&            \*(AqStr|Code|Math\*(Aq   => sub { $_\->content },
\&            \*(AqLineBreak|Space\*(Aq => sub { \*(Aq \*(Aq }
\&        } );
.Ve
.ie n .SS "transform( $ast, ... )"
.el .SS "transform( \f(CW$ast\fP, ... )"
.IX Subsection "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 \f(CW\*(C`undef\*(C'\fR or
\&\f(CW\*(C`\eundef\*(C'\fR), 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).
.PP
See also function \f(CW\*(C`pandoc_filter\*(C'\fR exported by Pandoc::Filter.
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
Copyright 2014\- Jakob Vo\*8
.PP
\&\s-1GNU\s0 General Public License, Version 2
.PP
This module is heavily based on Pandoc by John MacFarlane.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Haskell module Text.Pandoc.Walk <http://hackage.haskell.org/package/pandoc-types/docs/Text-Pandoc-Walk.html> for the original.