Ponder is an American Checkers Engine
=====================================

Rules [1]
-----

* Board - The board is an 8×8 grid, with alternating black and red squares,
called a checkerboard (in the U.S., in reference to its checkered pattern,
also the source of the name checkers). The playable surface consists of the 32
dark squares only. A consequence of this is that, from each player's
perspective, the left and right corners encourage different strategies.

* Pieces - The pieces are usually made of wood and are flat and cylindrical.
They are invariably split into one darker and one lighter color. Traditionally,
these colors are red and white. There are two kinds of pieces: "men" and
"kings". Kings are differentiated as consisting of two normal pieces of the
same color, stacked one on top of the other. Often indentations are added to
the pieces to aid stacking.

* Starting Position - Each player starts with 12 pieces on the three rows
closest to their own side, as shown in the diagram. The row closest to each
player is called the "crownhead" or "kings row". The black (darker color) side
moves first.

* How to Move - There are two ways to move a piece: simply sliding a piece
diagonally forwards (also diagonally backwards in the case of kings) to an
adjacent and unoccupied dark square, or "jumping" one of the opponent's pieces.
In this case, one piece "jumps over" the other, provided there is a vacant
square on the opposite side for it to land on. Again, a man (uncrowned piece)
can only jump diagonally forwards, and a king can also move diagonally
backwards. A piece that is jumped is captured and removed from the board.
Multiple-jump moves are possible if, when the jumping piece lands, there is
another piece that can be jumped. Jumping is mandatory and cannot be passed up
to make a non-jumping move, nor can fewer than the maximum jumps possible be
taken in a multiple-jump move. When there is more than one way for a player to
jump, one may choose which sequence to make, not necessarily the sequence that
will result in the most amount of captures. However, one must make all the
captures in that sequence. (Under traditional draughts rules jumping is not
mandatory. If it is not done, the opponent may either force the move to be
reversed, huff the piece or carry on regardless.)

* Kings - If a player's piece moves into the kings row on the opposing player's
side of the board, that piece is said to be "crowned" (or often "kinged" in the
U.S.), becoming a "king" and gaining the ability to move both forwards and
backwards. If a player's piece jumps into the kings row, the current move
terminates; having just been crowned, the piece cannot continue on by jumping
back out (as in a multiple jump), until the next move.

* How the Game Ends - A player wins by capturing all of the opposing player's
pieces, or by leaving the opposing player with no legal moves.

[1] http://en.wikipedia.org/wiki/English_draughts

Compiling
---------

Run command ``make'' to compiling. The main executable file is ``ponder''.

Playing
-------

The below chart show the user interface of the Ponder engine.  This is the
official game board of American checkers game, 8x8 size.  The squares are
marked from "1" to "32" at the lower left.

$ ponder
  +---+---+---+---+---+---+---+---+
  |   |(w)|   |(w)|   |(w)|   |(w)|
  +---+32-+---+31-+---+30-+---+29-+
  |(w)|   |(w)|   |(w)|   |(w)|   |
  +28-+---+27-+---+26-+---+25-+---+
  |   |(w)|   |(w)|   |(w)|   |(w)|
  +---+24-+---+23-+---+22-+---+21-+
  | \ |   | \ |   | \ |   | \ |   |
  +20-+---+19-+---+18-+---+17-+---+
  |   | \ |   | \ |   | \ |   | \ |
  +---+16-+---+15-+---+14-+---+13-+
  |(b)|   |(b)|   |(b)|   |(b)|   |
  +12-+---+11-+---+10-+---+9--+---+
  |   |(b)|   |(b)|   |(b)|   |(b)|
  +---+8--+---+7--+---+6--+---+5--+
  |(b)|   |(b)|   |(b)|   |(b)|   |
  +4--+---+3--+---+2--+---+1--+---+
;[FEN "B:W21,22,23,24,25,26,27,28,29,30,31,32:B1,2,3,4,5,6,7,8,9,10,11,12"]
  *** Black ***

(b) indecate a black man
(B) indicate a black king
(w) indicate a white man
(W) indicate a white king
 \  indicate an unoccupied dark square

Move a piece by type the starting square and the destination square with a dash
between them.

;[FEN "B:W21,22,23,24,25,26,27,28,29,30,31,32:B1,2,3,4,5,6,7,8,9,10,11,12"]
  +---+---+---+---+---+---+---+---+
  |   |(w)|   |(w)|   |(w)|   |(w)|
  +---+32-+---+31-+---+30-+---+29-+
  |(w)|   |(w)|   |(w)|   |(w)|   |
  +28-+---+27-+---+26-+---+25-+---+
  |   |(w)|   |(w)|   |(w)|   |(w)|
  +---+24-+---+23-+---+22-+---+21-+
  | \ |   | \ |   | \ |   | \ |   |
  +20-+---+19-+---+18-+---+17-+---+
  |   | \ |   | \ |   | \ |   | \ |
  +---+16-+---+15-+---+14-+---+13-+
  |(b)|   |(b)|   |(b)|   |(b)|   |
  +12-+---+11-+---+10-+---+9--+---+
  |   |(b)|   |(b)|   |(b)|   |(b)|
  +---+8--+---+7--+---+6--+---+5--+
  |(b)|   |(b)|   |(b)|   |(b)|   |
  +4--+---+3--+---+2--+---+1--+---+
  *** Black ***
10-14
;[FEN "W:W21,22,23,24,25,26,27,28,29,30,31,32:B1,2,3,4,5,6,7,8,9,11,12,14"]
  +---+---+---+---+---+---+---+---+
  |   |(w)|   |(w)|   |(w)|   |(w)|
  +---+32-+---+31-+---+30-+---+29-+
  |(w)|   |(w)|   |(w)|   |(w)|   |
  +28-+---+27-+---+26-+---+25-+---+
  |   |(w)|   |(w)|   |(w)|   |(w)|
  +---+24-+---+23-+---+22-+---+21-+
  | \ |   | \ |   | \ |   | \ |   |
  +20-+---+19-+---+18-+---+17-+---+
  |   | \ |   | \ |   |(b)|   | \ |
  +---+16-+---+15-+---+14-+---+13-+
  |(b)|   |(b)|   | \ |   |(b)|   |
  +12-+---+11-+---+10-+---+9--+---+
  |   |(b)|   |(b)|   |(b)|   |(b)|
  +---+8--+---+7--+---+6--+---+5--+
  |(b)|   |(b)|   |(b)|   |(b)|   |
  +4--+---+3--+---+2--+---+1--+---+

While capture a piece, use character x instead of dash.

;[FEN "B:W15,21,22,24,25,26,27,28,29,30,31,32:B1,2,3,4,5,6,8,9,10,11,12,14"]
  +---+---+---+---+---+---+---+---+
  |   |(w)|   |(w)|   |(w)|   |(w)|
  +---+32-+---+31-+---+30-+---+29-+
  |(w)|   |(w)|   |(w)|   |(w)|   |
  +28-+---+27-+---+26-+---+25-+---+
  |   |(w)|   | \ |   |(w)|   |(w)|
  +---+24-+---+23-+---+22-+---+21-+
  | \ |   | \ |   | \ |   | \ |   |
  +20-+---+19-+---+18-+---+17-+---+
  |   | \ |   |(w)|   |(b)|   | \ |
  +---+16-+---+15-+---+14-+---+13-+
  |(b)|   |(b)|   |(b)|   |(b)|   |
  +12-+---+11-+---+10-+---+9--+---+
  |   |(b)|   | \ |   |(b)|   |(b)|
  +---+8--+---+7--+---+6--+---+5--+
  |(b)|   |(b)|   |(b)|   |(b)|   |
  +4--+---+3--+---+2--+---+1--+---+
  *** Black ***
11x18
;[FEN "W:W21,22,24,25,26,27,28,29,30,31,32:B1,2,3,4,5,6,8,9,10,12,14,18"]
  +---+---+---+---+---+---+---+---+
  |   |(w)|   |(w)|   |(w)|   |(w)|
  +---+32-+---+31-+---+30-+---+29-+
  |(w)|   |(w)|   |(w)|   |(w)|   |
  +28-+---+27-+---+26-+---+25-+---+
  |   |(w)|   | \ |   |(w)|   |(w)|
  +---+24-+---+23-+---+22-+---+21-+
  | \ |   | \ |   |(b)|   | \ |   |
  +20-+---+19-+---+18-+---+17-+---+
  |   | \ |   | \ |   |(b)|   | \ |
  +---+16-+---+15-+---+14-+---+13-+
  |(b)|   | \ |   |(b)|   |(b)|   |
  +12-+---+11-+---+10-+---+9--+---+
  |   |(b)|   | \ |   |(b)|   |(b)|
  +---+8--+---+7--+---+6--+---+5--+
  |(b)|   |(b)|   |(b)|   |(b)|   |
  +4--+---+3--+---+2--+---+1--+---+

Use "help" or "?" in the game engine to show the help information.

help
    ?               Show this help information.
    analyze         Engine thinks about what move it make next if it were on
                    move.
    black           Set Black on move, and the engine will play White.
    force           Set the engine to play neither color ("force mode").
    go              Leave force mode and set the engine to play the color that
                    is on move.  Start thinking and eventually make a move.
    help            Show this help information.
    history         Show the record of moves.
    new             Reset the board to the standard starting position.
    ping N          N is a decimal number.  Reply by sending the string
                    "pong N"
    print           Show the current board.
    quit            Quit this program.
    rotate          Rotate the board 180 degrees.
    setboard FEN    Set up the pieces position on the board.
    sd DEPTH        The engine should limit its thinking to DEPTH ply.
    st TIME         Set the time control to TIME seconds per move.
    undo            Back up a move.
    verbose         Toggle verbose mode.
    white           Set White on move, and the engine will play Black.