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1 "Intersections & Splats" is an INTERCAL implementation of one of my
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2 favorite games, "Cows & Bulls," now more commonly known by the
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3 commercial version, "Mastermind."
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4
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5 Rules of the Game
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6
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7 The idea of the game is that one person selects a "code" in the form
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8 of a short string of digits, typically four. ("Mastermind" used colors
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9 in place of numbers.) The other person has a limited number of chances
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10 to guess what the code is. Every move consists of submitting a guess,
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11 and the first player replying with a score. Each scoring reveals a
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12 little more information about the code. A guess is scored by giving a
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13 certain number of cows and a certain number of bulls. These correspond
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14 to Mastermind's white pegs and black pegs, respectively - and, in this
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15 program, intersections (+) and splats (*).
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16
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17 This game is perfect for a computer because the person who makes the
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18 code has nothing to do but score the other player's guesses - a
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19 mechanical task.
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20
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21 Here's how the scoring works. For every number in the code that is
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22 matched by the same number in the same position in the guess, a splat
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23 is scored. And for every number in the code that is matched by the
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24 same number in the guess, but in the wrong position, an intersection,
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25 is scored.
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26
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27 For example: with a code of "3451" and a guess of "2465", one splat
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28 and one intersection would be earned. The splat is for the 4, and the
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29 intersection is for the 5. Of course, the player making the guesses
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30 isn't told which numbers earned what - that's what they have to
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31 deduce. A guess of "6152" gets exactly the same score, even though the
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32 intersection and splat correspond to completely different digits.
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33
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34 The game continues until the code is discovered or the player runs out
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35 of guesses.
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36
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37 Note that there can be some confusion about how the scoring works with
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38 repeated digits. In absence of a better standards body, I have stuck
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39 with the version described in the Mastermind rules, which is that a
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40 digit in the guess can match up with more than one digit in the code.
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41 Another example is in order. Say the code is "2412". A guess of "2544"
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42 would earn one splat and two intersections. The splat is for having a
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43 2 in the guess in the right position, and one of the intersections is
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44 also for having a 2 in the guess, but now in the wrong position. The
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45 final intersection is earned by having a 4 in the guess, again in the
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46 wrong position. The second 4 in the guess, however, does not affect
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47 the scoring.
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48
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49 Here is an algorithmic description of how scoring is done. The player
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50 looks at each digit in the code in turn. If the digit under
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51 consideration is matched by the same digit in the same place, a splat
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52 is earned. Otherwise, if any other digit in the guess is the same, an
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53 intersection is earned.
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54
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55 For those conversant in C, here is an even more algorithmic
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56 description:
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57
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58 for (i = 0 ; i < digits ; ++i)
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59 if (guess[i] == code[i])
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60 ++splats;
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61 else
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62 for (j = 0 ; j < digits ; ++j)
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63 if (guess[j] == code[i]) {
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64 ++intersections;
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65 break;
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66 }
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67
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68 For those conversant in INTERCAL, consult the source code.
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69
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70 Anyway, enough of this. Play the game a few times; you'll get the idea.
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71
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72 How To Play
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73
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74 At each move the board is displayed, which shows you all of your
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75 previous guesses. Above each guess are the intersections and splats
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76 that they earned. Here is an example of a game in progress:
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77
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78 +
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79 * + + * *
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80 (1) (5) (2) ( ) ( ) ( ) ( ) ( ) ( ) ( ) (?)
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81 (2) (4) (4) ( ) ( ) ( ) ( ) ( ) ( ) ( ) (?)
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82 (4) (4) (3) ( ) ( ) ( ) ( ) ( ) ( ) ( ) (?)
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83 (2) (6) (5) ( ) ( ) ( ) ( ) ( ) ( ) ( ) (?)
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84
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85 The first guess "1242" earned one splat and one intersection. The
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86 third guess "2435" earned two splats and one intersection. The player
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87 has seven more guesses left. Guesses are typed in at the "MOVE:"
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88 prompt.
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89
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90 At the end of the game, the questions marks at the right are replaced
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91 with the code. You are then prompted with "[CNQ]". Enter N to start a
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92 new game, Q to quit playing, or C to configure the game (see below). N
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93 is the default, so if you just hit enter, or type anything except C or
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94 Q, it has the same effect. You can also use any of these commands at
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95 the "MOVE:" prompt, if you wish to abandon the current game. In
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96 addition, R can be entered during a game to redraw the board.
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97
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98 Configuring the Game
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99
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100 The game is set up originally to have ten guesses in a game, four
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101 digits in the code, and to use the digits 1 through 6. (This matches
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102 the setup of the "Mastermind" game.) The C command can be used to
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103 modify these settings, so as to change the difficulty of the game.
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104
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105 When you enter the C command, you are first prompted for the X
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106 setting, the number of guesses allowed; then the Y setting, which is
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107 the number of digits in the code; and finally the N setting, the
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108 number of digits used in the game. Each number is entered using
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109 standard INTERCAL numeric entry. (Yes, I could have used my own numio
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110 routines here, but the program is big enough as it is. Besides, I
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111 didn't want you to completely forget that you were using an INTERCAL
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112 program.) You can enter ZERO at any three prompts to abort the
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113 configuration and return to the current game. If any values are higher
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114 than ONE FIVE, the value modulo 16 will be used instead. Note that
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115 while you can enter a value higher than NINE for the number of digits,
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116 you may need to have an ASCII chart handy. (By the way, if anyone
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117 wants an EBCDIC version, drop me a line.)
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118
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119 Other Versions
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120
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121 I enjoyed writing this program so much, that I created two others
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122 based on it. First, there is a colorized version, which requires a
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123 VT100/ANSI color terminal, or something compatible. And second, there
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124 is a CGI script version that plays this game. A package containing all
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125 three versions is available at ftp.muppetlabs.com under
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126 /pub/intercal/ins.tar.gz. In addition, you can play the CGI script at
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127 http://www.muppetlabs.com/~breadbox/intercal/ins/insstart.html.
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128
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129 Coda
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130
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131 That's it. Have fun. Questions, comments, and concerns for my mental
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132 health can be directed to breadbox@muppetlabs.com.
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