reverse_utf8 Function

   pure function reverse_utf8(str) result(retval)
      use :: forgex_parameters_m
      implicit none
      character(*), intent(in) :: str
      character(:), allocatable :: retval

      integer :: i, ie

      ! Initialize
      ie = 1
      i = 1
      retval = ''
      do while (i /= INVALID_CHAR_INDEX)
         ie = idxutf8(str, i)
         retval = str(i:ie)//retval
         i = next_idxutf8(str, i)
      end do 
   end function reverse_utf8