There are many ways to build tree-like data-structures in perl, and I am currently trying to build a list of them (specifically n-ary trees and without using objects or modules (more about this reasoing later on)). I am looking for examples from other monks on how they create trees, or have created trees in the past or even of tree structures they know that common modules require/return. I currently have the following examples.

The straight forward recursive data-structure approach:

# the nested array refs
my $tree = [
           'Root', [
                 'Child1', [
                       'GrandChild1',
                       'GrandChild2'
                 ],
                 'Child2'
           ]
];

# the nested hash references
my $tree = {
           'Root' => {
                 'Child1' => {
                       'GrandChild1' => {},
                       'GrandChild2' => {}
                 },
                 'Child2' => {}
           }
};
[download]

And the more complex relational approach:

# using arrays where 
# the array index is 
# the id refered to by 
# the parent_id
my $tree = [
        # parent_id, node
       [ undef, 'Root' ],
       [  0, 'Child1' ],
       [  0, 'Child2' ],
       [  1, 'GrandChild1' ],
       [  1, 'GrandChild2' ]
];

# using hashes in a similar manner
my $tree = [
       { id => 0, parent_id => undef, node => 'Root' },
       { id => 1, parent_id => 0, node => 'Child1' },
       { id => 2, parent_id => 0, node => 'Child2' },
       { id => 3, parent_id => 1, node => 'GrandChild1' },
       { id => 4, parent_id => 1, node => 'GrandChild2' }
];
[download]

Now for my reasoning.

I am the author of a module called Tree::Simple which is a basic object-oriented n-ary tree. I have also created a small set of Visitor classes for use with this module at Tree::Simple::VisitorFactory which right now it's mostly pretty basic stuff. However, I am in the process of getting ready to release the next version of Tree::Simple::VisitorFactory which has about twice as many Visitors in it (hopefully many useful ones). I am currently putting together a set of Visitors to do conversions (both to and from) other tree representations, so I am looking for examples from as many people as possible to be sure I cover as many styles of trees in perl as possible. Any help is very much appreciated.

Thanks in advance,

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