code: public static <I, O> Supplier<O> map( Supplier<I> source, Function<I, O> map )
      {
          return () -> map.apply( source.get() );
      }
docs: Convert the value supplied by a {@link Supplier} by passing it through a {@link Function}.
  
  @param source the source supplier that supplies the original value.
  @param map    the function that converts the value of the original supplier.
  @param <I>    the type of the value supplied by the original supplier.
  @param <O>    the type of the value supplied by the resulting supplier.
  @return a converting supplier.