code: function walkNodesBreadthFirstHelper(ast, f) {
    let childAst = [];
    (ast || []).forEach(node => {
      f(node);
      childAst = childAst.concat(getChildren(node));
    });
    if (childAst.length > 0) {
      walkNodesBreadthFirstHelper(childAst, f);
    }
  }
docs: Helper function for walkNodeBreadthFirst