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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Newbie question
Date: Thu, 12 Mar 2009 06:48:36 -0700 (PDT)
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Date: 2009-03-12T06:48:36-07:00
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On Mar 12, 2:29=A0pm, Olivier Scalbert <olivier.scalb...@algosyn.com>
wrote:
> Hello,
>
> I start learning Ada and I try to define types for a chess engine.
>
> I have create some "obvious" types:
>
> =A0 =A0 =A0type Color_T is (White, Black);
>
> =A0 =A0 =A0type PieceType_T is (Pawn, Knight, Bishop, Rook, Queen, King);
>
> =A0 =A0 =A0type Piece_T is record
> =A0 =A0 =A0 =A0 =A0Color: Color_T;
> =A0 =A0 =A0 =A0 =A0PieceType: PieceType_T;
> =A0 =A0 =A0end record;
>
> Now, I want to create an array of 64 squares representing the chess
> board. A square should contain nothing or a Piece_T
>
> I have tried:
>
> =A0 =A0 =A0type Board_T is array(1..64) of Piece_T;
>
> But I can not have an empty square !
>
> What is the best way of doing that ?
>
> Thanks,
>
> Olivier

Solution 1: a variant record:

type Square_T (Empty : Boolean) is record
   case Empty is
      when True =3D> null;
      when False =3D> Piece : Piece_T;
   end case;
end record;

type Board_T is array (1 .. 8, 1 .. 8) of Square_T;

Solution 2: merge the Boolean directly into Piece_T:

type Piece_T (Present : Boolean) is record
   case Present is
      when True =3D>
         Color : Color_T;
         Piece_Type : Piece_Type_T;
      when False =3D>
         null;
   end case;
end record;

Solution 3: introduce a new value for Piece_Type_T:

type Piece_Type_T is (None, Pawn, Knight, Bishop, Rook, Queen, King);

I don't know which is the best solution; perhaps you'd like to try
them all and see how well they integrate with the algorithms.  I think
Solution 3 is the most error-prone, though.

--
Ludovic Brenta;