 a depth first, pre-order traversal over a data structure.
Also allow for callbacks before and after visiting the children
of a node. Also allow for a custom `get-children` function to
change traversal as needed. Will detect cycles if an empty table
is passed as the `seen` parameter, which is used to cached values
that have been visited.</pre><a href="https://janetdocs.org/misc/dfs">Community Examples</a></div><hr><div class="binding"><span id="misc/do-def" class="binding-sym">misc/do-def</span> <span class