Attean::TreeRewriter(3) Walk and rewrite subtrees


This document describes Attean::TreeRewriter version 0.017


use v5.14;
use Attean;
my $w = Attean::TreeRewriter->new();
my ($rewritten, $tree) = $w->rewrite($tree, $thunk);
if ($rewritten) {


The Attean::TreeRewriter class walks the nodes of query trees and rewrites sub-trees based on handlers that have been registered prior to rewriting.




"register_pre_handler( \&code )"
Register a handler that will be called for each sub-tree during tree rewriting.

The function will be called as "&code( $tree, $parent_node, $thunk )" where $thunk is an opaque value passed to "rewrite".

The function must return a list "($handled, $descend, $rewritten)". $handled is a boolean indicating whether the handler function rewrote the sub-tree, which is returned as $rewritten. The $descend boolean value indicates whether the the tree rewriting should continue downwards in the tree.

"rewrite( $tree, $thunk, \%seen, $parent )"
Rewrites the given $tree using the registered handler functions. $thunk is passed through to each handler function. %seen is currently unused. $parent is passed through to the handler functions as the value of the pseudo-parent tree node for $tree.

Returns a list "($handled, $tree)" with $handled indicating whether rewriting was performed, with the corresponding rewritten $tree.


Please report any bugs or feature requests to through the GitHub web interface at <>.


Gregory Todd Williams "<[email protected]>"


Copyright (c) 2014--2016 Gregory Todd Williams. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.