code: func (f *walkFilesystem) Walk(root string, walkFn WalkFunc) error {
  	info, err := f.Lstat(root)
  	if err != nil {
  		return walkFn(root, nil, err)
  	}
  	return f.walk(root, info, walkFn)
  }
docs: // Walk walks the file tree rooted at root, calling walkFn for each file or
  // directory in the tree, including root. All errors that arise visiting files
  // and directories are filtered by walkFn. The files are walked in lexical
  // order, which makes the output deterministic but means that for very
  // large directories Walk can be inefficient.
  // Walk does not follow symbolic links.