whole_func_string: function fmap(f, tree) {
    return new RoseTree(
      f(tree.root),
      function() {
        return tree.children().map(fmap.bind(null, f));
      }
    );
  }
func_code_string: function fmap(f, tree) {
    return new RoseTree(
      f(tree.root),
      function() {
        return tree.children().map(fmap.bind(null, f));
      }
    );
  }
func_documentation_string: (a -> b) -> RoseTree a -> RoseTree b