Interpreter

Interpreter walks the tree starting at the root.

Visits the tree, starting with the root and finally the leaves (top-down)

For each tree node, it calls its methods (provided by user via inheritance) according to ``tree.data``.

Unlike ``Transformer`` and ``Visitor``, the Interpreter doesn't automatically visit its sub-branches.
The user has to explicitly call ``visit``, ``visit_children``, or use the ``@visit_children_decor``.
This allows the user to implement branching and loops.

Interpreter walks the tree starting at the root.

Visits the tree, starting with the root and finally the leaves (top-down)

For each tree node, it calls its methods (provided by user via inheritance) according to ``tree.data``.

Unlike ``Transformer`` and ``Visitor``, the Interpreter doesn't automatically visit its sub-branches.
The user has to explicitly call ``visit``, ``visit_children``, or use the ``@visit_children_decor``.
This allows the user to implement branching and loops.