code: def _watch_folder(folder, destination, compiler_args):
      
      for dirpath, dirnames, filenames in os.walk(folder):
          for filename in filenames:
              # Ignore filenames starting with ".#" for Emacs compatibility
              if watched_extension(filename) and not filename.startswith('.#'):
                  fullpath = os.path.join(dirpath, filename)
                  subfolder = os.path.relpath(dirpath, folder)
                  mtime = os.stat(fullpath).st_mtime
                  
                  # Create subfolders in target directory if they don't exist
                  compiled_folder = os.path.join(destination, subfolder)
                  if not os.path.exists(compiled_folder):
                      os.makedirs(compiled_folder)
                  
                  compiled_path = _compiled_path(compiled_folder, filename)
                  if (not fullpath in compiled or
                      compiled[fullpath] < mtime or
                      not os.path.isfile(compiled_path)):
                      compile_file(fullpath, compiled_path, compiler_args)
                      compiled[fullpath] = mtime
docs: Compares "modified" timestamps against the "compiled" dict, calls compiler
      if necessary.