Ada get Character input and check if it is a valid input - character

Question

with Ada.Text_IO, Ada.Integer_Text_IO, Ada.Characters.Handling;
with Ada.Exceptions; use Ada.Exceptions;
USE Ada, Ada.Text_Io;
WITH connectfour;
PROCEDURE Main IS
PACKAGE board is new connectfour;
USE board;
col : Character;
function checkInput (input : Character) RETURN BOOLEAN is
ins : Character := input;
begin
ins := Ada.Characters.Handling.To_Lower(ins);
if ins = 'a' or ins = 'b' or ins = 'c' or ins = 'd' or
ins = 'e' or ins = 'f' or ins = 'g' or ins = 'h' then
return true;
end if;
return false;
end checkInput;
begin
board.initialize;
board.print;
while (not board.isFull) loop
loop
PUT("Player"&Integer'Image(board.turn)&": ");
Ada.Text_IO.Get(col);
exit when checkInput(col);
end loop;
exit when col = '0';
Text_IO.New_Line;
Text_IO.Put ("");
board.play(col);
end loop;
end Main;
So when I run my program I get:
Player 1: a --> (I entered the character 'a' and clicked enter)
Then I keep getting this error right after, at the line "Ada.Text_IO.Get(col);"
raised ADA.IO_EXCEPTIONS.DATA_ERROR : a-tiinio.adb:86 instantiated at a-inteio.ads:18
What I want to do, is get a single character input from the user and check if it is within the range A .. H, if yes, then exit the loop, otherwise keep asking...
I cannot find out what my issue is...
I allow the user to enter lowercase or uppercase characters, and I convert uppercase to lowercase and perform a check.
Please help...
I am not sure how to read in a single Character....

Answer 1

Okay the exception message could be clearer (and there are ways to get stack traces when one happens but let's work with what we've got...)
locate a-tiinio.adb
/usr/lib/gcc/x86_64-linux-gnu/4.9/rts-native/adainclude/a-tiinio.adb
which is
package body Ada.Text_IO.Integer_IO
and line 86 is an exception raised in
procedure Get
(Item : out Num;
Width : Field := 0)
Details don't matter (yet) but I cannot see any calls to Ada.Text_IO.Integer_IO.Get.
So my suspicion is that the code shown is working
(as well as can be expected : NOTE HOWEVER there is no way to get to exit when col = '0'; with col outside a .. h) and there is another call to Get (this time Integer_IO.Get) buried in board.play. It would be easy to test this by printing col= before calling board.play.
Minor style comment:
function checkInput (input : Character) RETURN BOOLEAN is
ins : Character := input;
begin
ins := Ada.Characters.Handling.To_Lower(ins);
can be simplified
function checkInput (input : Character) RETURN BOOLEAN is
ins : Character := Ada.Characters.Handling.To_Lower(input);
begin