Guide to Assignment 4 support code

The code for this assignment is in two different files: one with compiled Scheme code, a4code.com, and one source code file connect4.scm. The former contains support code for the Nim and Coin-strip games. Support code for the Connect 4 game is in both files. You should load both files from your Scheme code file. The information on this page is organized into the following sections:

Nim
Coin-strip
Connect 4
Other support functions

whuang@cs.rpi.edu; email
Last updates: October 11; September 30, 2000

Nim

The following procedures are defined:

(nim-end? state)
(nim-gc state)
As described in the assignment.
(print-nim-game return-val)
Given a proper return value from minimax, this function will nicely print out the sequence of moves in the game and who won. For example: (print-nim-game (minimax '(0 2 1) nim-gc nim-end?))
(play-nim start-state)
(play-nim start-state #t)
Lets you play Nim against your minimax function. If a second argument of #t is given, you get to go first.

Coin-strip

The following procedure is defined:

(play-coin start-state)
(play-coin start-state #t)
Lets you play Coin-strip against your minimax function. If a second argument of #t is given, you get to go first.

Connect 4

The support code for Connect 4 is split between the a4code.com and connect4.scm. The code you need to see (mostly that code which deals with the board representation and functions to analyze a board) appears in the latter. Code that you don't really need to see appears in the former. The file where each function is defined appears in the documentation below.

In addition, read the comments in connect4.scm. There are some extensive comments there about how to get started and about the board representation. These functions are organized into the following sections:

Board representation and accessors
Playing Connect 4
Functions for analyzing a Connect 4 board

Board representation and accessors

(board-string board)
(pieces-list board)
[connect4] Accessors for parts of the board representation. See comments in connect4.scm
(piece-at board row col)
[connect4] Returns either X, O, or empty.
(c4-children board player)
[connect4] Returns a list of the children of the given board, formed by the given player (either X or O) making a valid move.
(valid-moves board)
[connect4] Returns a list of valid moves.
(c4-end? board)
[connect4] Returns either X, O, draw, or #f.
c4-start
[connect4] The representation for the starting (empty) board.

Playing Connect 4

(play-c4 x-player o-player)
(play-c4 x-player o-player #t)
[a4code] Runs a game between two players. The x-player and o-player arguments must be player functions, i.e. functions that take a board and the player (X or O) and returns a move (an integer between 1 and 7 inclusive). The X player always goes first. Also see the comments in the connect4.scm file for more information.
(human-player board player)
[connect4] A player function that asks you what move you want to make.
(random-player board player)
[connect4] A player function that picks a random move.

Functions for analyzing a Connect 4 board

These functions should be useful for creating your evaluation function.

(open-columns board player)
(open-rows board player)
(open-diagonals board player)
[connect4] Returns the number of open sequences of pieces. By "open," I mean a sequence that can be extended into a longer sequence: the sequence does not end at the edge of the board nor is it "blocked" by an opponent's piece. See the connect4.scm file for information on what these functions return

Other useful functions

Counting states

I am providing a mechanism for you to count the number of states that you evaluate without having to pass an extra argument to all your functions. The following functions provide a way to manipulate a global counter.

(reset-sc)
[a4code] Resets the state count to 0.
(inc-sc count)
[a4code] Increments the state count by count.
(get-sc)
[a4code] Returns the state count.

Handing infinity

I am providing a few functions that operate on the real numbers extended to include the symbols pos-infinity and neg-infinity. These functions are all in a4code.com.

(inf:max a b)
(inf:min a b)
(inf:>= a b)
(inf:<= a b)
(inf:> a b)
(inf:< a b)
(inf:= a b)

Note that the inf:max and inf:min functions only handle two arguments, unlike the regular max and min functions.