code: def nltk_stemmer(stemmer, token, i=None, tokens=None):
      
  
      def wrapped_stem(token, metadata=None):
          return stemmer.stem(token)
  
      return token.update(wrapped_stem)
docs: Wrapper around a NLTK SnowballStemmer, which includes stop words for
      each language.
  
      Args:
          stemmer (SnowballStemmer): Stemmer instance that performs the stemming.
          token (lunr.Token): The token to stem.
          i (int): The index of the token in a set.
          tokens (list): A list of tokens representing the set.