code: public <NL> @NonNull Pair<NL, R> lmap(final @NonNull Function<? super L, ? extends NL> function) {
      return new Pair<>(function.apply(this.left), this.right);
    }
docs: Map the left value of this pair.
  
  @param function the function
  @param <NL> the left type
  @return a new pair