init_input_list Subroutine

  subroutine init_input_list(list)
    type(input_list),optional :: list
    if(present(list))then
       allocate(list%root)    
       list%size=0
       list%status=.true.
       list%root%next=>null()
    else
       allocate(default_list%root)    
       default_list%size=0
       default_list%status=.true.
       default_list%root%next=>null()
    endif
  end subroutine init_input_list