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Date: 16 Nov 91 21:45:23 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!uwm.edu!ogicse!milton!mfeldm
an@ucbvax.Berkeley.EDU  (Michael Feldman)
Subject: Portable End_Error handling desired
Message-ID: <1991Nov16.214523.8324@milton.u.washington.edu>
List-Id: <comp.lang.ada>

Ever in search of the elusive portability will-o'-the-wisp, I ask
your help in testing the behavior of this program. The idea is to 
keep the program alive, whatever the nature of the input. (Yes,
I know the best way to do this is read the input line into a string,
etc., but don't want to do it this way).

The program's behavior is predictable and portable EXCEPT when EOF is
entered from the keyboard (ctrl-D on Unix, ctrl-Z on DOS, etc.).
Tests on 6 different compilers produce at least 3 different behaviors,
including in certain cases an undesired propagation of End_Error
out of the exception loop, back to the runtime. Any ideas, Ada fans?

Mike

PS - the behavior if a float literal, or similar, with digits preceding
a non-integer character, is undesirable but portable. I know this.

-- cut here for program

WITH Text_IO;
PROCEDURE ExceptionLoop IS

  PACKAGE My_Int_IO IS New Text_IO.Integer_IO(Integer);

  MinVal : CONSTANT Integer := -10;
  MaxVal : CONSTANT Integer :=  10;
  SUBTYPE SmallInt  IS Integer RANGE MinVal .. MaxVal;

  InputValue: SmallInt;
  Sum:        Integer;
            
BEGIN -- ExceptionLoop

  Sum := 0;

  FOR Count IN 1..5 LOOP -- counts the five values we need to read

    LOOP      -- inner loop just to control robust input
      BEGIN   -- block for exception handler

        Text_IO.Put(Item => "Enter an integer between ");
        My_Int_IO.Put(Item => SmallInt'First, Width => 0);  
        Text_IO.Put(Item => " and ");
        My_Int_IO.Put(Item => SmallInt'Last, Width => 0);  
        Text_IO.Put(Item => " > ");
        My_Int_IO.Get(Item => InputValue);

        EXIT; -- leave the loop only upon correct input

      EXCEPTION
        WHEN Constraint_Error =>
          Text_IO.Put ("Value entered is out of range. Please try again.");
          Text_IO.New_Line;
        WHEN Text_IO.End_Error =>
          Text_IO.Put ("We are not done yet. Don't enter EOF!");
          Text_IO.New_Line;
          Text_IO.Skip_Line;
        WHEN Text_IO.Data_Error =>
          Text_IO.Put ("Value entered not an integer. Please try again.");
          Text_IO.New_Line;
          Text_IO.Skip_Line;

      END;    -- block for exception handler
    END LOOP;
    -- assert: InputValue is in the range MinN to MaxN   

    Sum := Sum + InputValue; -- add new value into Sum
  END LOOP;

  Text_IO.Put (Item => "The sum is ");
  My_Int_IO. Put (Item => Sum, Width => 1);
  Text_IO.New_Line;

END ExceptionLoop;