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选题[tech]: 20200729 Demonstrating Perl with Tic-Tac-Toe, Part 4
sources/tech/20200729 Demonstrating Perl with Tic-Tac-Toe, Part 4.md
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[#]: collector: (lujun9972)
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[#]: translator: ( )
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (Demonstrating Perl with Tic-Tac-Toe, Part 4)
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[#]: via: (https://fedoramagazine.org/demonstrating-perl-with-tic-tac-toe-part-4/)
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[#]: author: (Gregory Bartholomew https://fedoramagazine.org/author/glb/)
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Demonstrating Perl with Tic-Tac-Toe, Part 4
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======
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![][1]
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This is the final article to the series demonstrating Perl with Tic-Tac-Toe. This article provides a module that can compute better game moves than the previously presented modules. For fun, the modules _chip1.pm_ through _chip3.pm_ can be incrementally moved out of the _hal_ subdirectory in reverse order. With each chip that is removed, the game will become easier to play. The game must be restarted each time a chip is removed.
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### An example Perl program
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Copy and paste the below code into a plain text file and use the same one-liner that was provided in the [the first article][2] of this series to strip the leading numbers. Name the version without the line numbers _chip3.pm_ and move it into the _hal_ subdirectory. Use the version of the game that was provided in [the second article][3] so that the below chip will automatically load when placed in the _hal_ subdirectory. Be sure to also include both _chip1.pm_ and _chip2.pm_ from the second [and third][4] articles, respectively, in the _hal_ subdirectory.
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```
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00 # artificial intelligence chip
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01
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02 package chip3;
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03 require chip2;
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04 require chip1;
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05
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06 use strict;
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07 use warnings;
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08
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09 sub moverama {
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10 my $game = shift;
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11 my @nums = $game =~ /[1-9]/g;
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12 my $rama = qr/[1973]/;
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13 my %best;
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14
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15 for (@nums) {
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16 my $ra = $_;
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17 next unless $ra =~ $rama;
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18 $best{$ra} = 0;
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19 for (@nums) {
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20 my $ma = $_;
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21 next unless $ma =~ $rama;
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22 if (($ra-$ma)*(10-$ra-$ma)) {
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23 $best{$ra} += 1;
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24 }
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25 }
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26 }
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27
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28 @nums = sort { $best{$b} <=> $best{$a} } keys %best;
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29
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30 return $nums[0];
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31 }
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32
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33 sub hal_move {
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34 my $game = shift;
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35 my $mark = shift;
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36 my @mark = @{ shift; };
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37 my $move;
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38
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39 $move = chip2::win_move $game, $mark, \@mark;
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40
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41 if (not defined $move) {
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42 $mark = ($mark eq $mark[0]) ? $mark[1] : $mark[0];
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43 $move = chip2::win_move $game, $mark, \@mark;
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44 }
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45
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46 if (not defined $move) {
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47 $move = moverama $game;
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48 }
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49
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50 if (not defined $move) {
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51 $move = chip1::hal_move $game;
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52 }
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53
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54 return $move;
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55 }
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56
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57 sub complain {
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58 print 'Just what do you think you\'re doing, ',
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59 ((getpwnam($ENV{'USER'}))[6]||$ENV{'USER'}) =~ s! .*!!r, "?\n";
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60 }
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61
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62 sub import {
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63 no strict;
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64 no warnings;
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65
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66 my $p = __PACKAGE__;
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67 my $c = caller;
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68
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69 *{ $c . '::hal_move' } = \&{ $p . '::hal_move' };
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70 *{ $c . '::complain' } = \&{ $p . '::complain' };
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71
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72 if (&::MARKS->[0] ne &::HAL9K) {
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73 @{ &::MARKS } = reverse @{ &::MARKS };
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74 }
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75 }
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76
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77 1;
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```
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### How it works
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Rather than making a random move or making a move based on probability, this final module to the Perl Tic-Tac-Toe game uses a more [deterministic][5] algorithm to calculate the best move.
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The big takeaway from this Perl module is that it is yet another example of how references can be misused or abused, and as a consequence lead to unexpected program behavior. With the addition of this chip, the computer learns to cheat. Can you figure out how it is cheating? Hints:
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1. Constants [are implemented as subroutines][6].
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2. References allow data to be modified out of scope.
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### Final notes
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Line 12 demonstrates that a regular expression can be [pre-compiled][7] and stored in a scalar for later use. This is useful as performance optimization when you intend to re-use the same regular expression many times over.
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Line 59 demonstrates that [some system library calls][8] are available directly in Perl’s built-in core functionality. Using the built-in functions alleviates some overhead that would otherwise be required to launch an external program and setup the I/O channels to communicate with it.
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Lines 72 and 73 demonstrate the use of **&::** as [a shorthand for **&main::**][9].
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The full source code for this Perl game can be cloned from the git repository available here: <https://pagure.io/tic-tac-toe.git>
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--------------------------------------------------------------------------------
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via: https://fedoramagazine.org/demonstrating-perl-with-tic-tac-toe-part-4/
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作者：[Gregory Bartholomew][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://fedoramagazine.org/author/glb/
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[b]: https://github.com/lujun9972
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[1]: https://fedoramagazine.org/wp-content/uploads/2020/02/perl-tic-tac-toe-816x346.png
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[2]: https://fedoramagazine.org/demonstrating-perl-with-tic-tac-toe-part-1/
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[3]: https://fedoramagazine.org/demonstrating-perl-with-tic-tac-toe-part-2/
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[4]: https://fedoramagazine.org/demonstrating-perl-with-tic-tac-toe-part-3/
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[5]: https://en.wikipedia.org/wiki/Deterministic_system
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[6]: https://perldoc.perl.org/5.32.0/constant.html#TECHNICAL-NOTES
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[7]: https://perldoc.perl.org/5.8.2/perlretut.html#Compiling-and-saving-regular-expressions
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[8]: https://perldoc.perl.org/5.8.2/functions/getpwnam.html
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[9]: https://perldoc.perl.org/perlmod.html#Packages
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