[eichin:19960613.2333PDT] exercise 3.1

package Buffer_System is
  type Buffer is private;
  procedure Load(B: out Buffer; S: in String);
  -- wrong: needs inout procedure Load(B: in out Buffer; S: in String);
  procedure Get(B: in out Buffer; C: out Character);
  function Is_Empty() return Boolean;
  -- wrong: shoudld be function Is_Empty(B: in Buffer) return Boolean;
  Error: exception;
  private 
     Max: constant Integer := 80;
     type Buffer is 
	record
	   Data: String(1..Max);
	   Start: Integer := 1;
	   Finish: Integer := 0;
	end record;
end Buffer_System;

package body Buffer_System is
   procedure Load(B: out Buffer; S: in String) is
   -- wrong: needs inout procedure Load(B: in out Buffer; S: in String) is
   begin
      -- start > finish if empty
      -- if S'Length>Max or not Is_Empty() then ??
      if S'Length > Max or B.Start <= B.Finish then
	 raise Error;			-- too long or characters left
      end if;
      B.Start = 1;
      B.Finish = S'Length;
      B.Data (B.Start .. B.Finish) := S; -- rest of file lost! [eichin:19971226.2156EST]