问Ada引发的Constraint_error：“值”的错误输入：

EN

WITH Ada.Text_IO, Ada.Integer_Text_IO;
USE Ada.Text_IO, Ada.Integer_Text_IO;

PROCEDURE Isbntest IS

  FUNCTION Strip(The_String: String; The_Characters: String)
        RETURN String IS
     Keep: ARRAY (Character) OF Boolean := (OTHERS => True);
     Result: String(The_String'RANGE);
     Last: Natural := Result'First-1;
  BEGIN
     FOR I IN The_Characters'Range LOOP
        Keep(The_Characters(I)) := False;
     END LOOP;
     FOR J IN The_String'RANGE LOOP
        IF Keep(The_String(J)) THEN
           Last := Last+1;
           Result(Last) := The_String(J);
        END IF;
     END LOOP;
     RETURN Result(Result'First .. Last);
  END Strip;


  Input: File_Type := Ada.Text_IO.Standard_Input;

BEGIN

   WHILE NOT End_of_File(Input) LOOP
     DECLARE 
     Line : String := Ada.Text_IO.Get_Line(Input);
     StrippedLine : String := line;
     ascii_val: Integer :=0;

  BEGIN
     StrippedLine := Strip(Line, "-");         
     ascii_val := integer'value(StrippedLine);
     Put(ascii_val);
     Put_line(StrippedLine);
  END;
   END LOOP;
   Close (Input);
end isbntest;