code: func WithLemmatizer(l lingo.Lemmatizer) TrainerConsOpt {
  	f := func(t *Trainer) {
  		// cannot pass in itself!
  		if T, ok := l.(*Trainer); ok && T == t {
  			panic("Recursive definition of lemmatizer (trying to set the t.lemmatizer = T) !")
  		}
  
  		t.l = l
  	}
  	return f
  }
docs: // WithLemmatizer sets the lemmatizer option on the Trainer