[#]: collector: (lujun9972) [#]: translator: ( ) [#]: reviewer: ( ) [#]: publisher: ( ) [#]: url: ( ) [#]: subject: (Demonstrating Perl with Tic-Tac-Toe, Part 4) [#]: via: (https://fedoramagazine.org/demonstrating-perl-with-tic-tac-toe-part-4/) [#]: author: (Gregory Bartholomew https://fedoramagazine.org/author/glb/) Demonstrating Perl with Tic-Tac-Toe, Part 4 ====== ![][1] 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. ### An example Perl program 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. ``` 00 # artificial intelligence chip 01 02 package chip3; 03 require chip2; 04 require chip1; 05 06 use strict; 07 use warnings; 08 09 sub moverama { 10 my $game = shift; 11 my @nums = $game =~ /[1-9]/g; 12 my $rama = qr/[1973]/; 13 my %best; 14 15 for (@nums) { 16 my $ra = $_; 17 next unless $ra =~ $rama; 18 $best{$ra} = 0; 19 for (@nums) { 20 my $ma = $_; 21 next unless $ma =~ $rama; 22 if (($ra-$ma)*(10-$ra-$ma)) { 23 $best{$ra} += 1; 24 } 25 } 26 } 27 28 @nums = sort { $best{$b} <=> $best{$a} } keys %best; 29 30 return $nums[0]; 31 } 32 33 sub hal_move { 34 my $game = shift; 35 my $mark = shift; 36 my @mark = @{ shift; }; 37 my $move; 38 39 $move = chip2::win_move $game, $mark, \@mark; 40 41 if (not defined $move) { 42 $mark = ($mark eq $mark[0]) ? $mark[1] : $mark[0]; 43 $move = chip2::win_move $game, $mark, \@mark; 44 } 45 46 if (not defined $move) { 47 $move = moverama $game; 48 } 49 50 if (not defined $move) { 51 $move = chip1::hal_move $game; 52 } 53 54 return $move; 55 } 56 57 sub complain { 58 print 'Just what do you think you\'re doing, ', 59 ((getpwnam($ENV{'USER'}))[6]||$ENV{'USER'}) =~ s! .*!!r, "?\n"; 60 } 61 62 sub import { 63 no strict; 64 no warnings; 65 66 my $p = __PACKAGE__; 67 my $c = caller; 68 69 *{ $c . '::hal_move' } = \&{ $p . '::hal_move' }; 70 *{ $c . '::complain' } = \&{ $p . '::complain' }; 71 72 if (&::MARKS->[0] ne &::HAL9K) { 73 @{ &::MARKS } = reverse @{ &::MARKS }; 74 } 75 } 76 77 1; ``` ### How it works 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. 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: 1. Constants [are implemented as subroutines][6]. 2. References allow data to be modified out of scope. ### Final notes 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. 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. Lines 72 and 73 demonstrate the use of **&::** as [a shorthand for **&main::**][9]. The full source code for this Perl game can be cloned from the git repository available here: -------------------------------------------------------------------------------- via: https://fedoramagazine.org/demonstrating-perl-with-tic-tac-toe-part-4/ 作者：[Gregory Bartholomew][a] 选题：[lujun9972][b] 译者：[译者ID](https://github.com/译者ID) 校对：[校对者ID](https://github.com/校对者ID) 本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出 [a]: https://fedoramagazine.org/author/glb/ [b]: https://github.com/lujun9972 [1]: https://fedoramagazine.org/wp-content/uploads/2020/02/perl-tic-tac-toe-816x346.png [2]: https://fedoramagazine.org/demonstrating-perl-with-tic-tac-toe-part-1/ [3]: https://fedoramagazine.org/demonstrating-perl-with-tic-tac-toe-part-2/ [4]: https://fedoramagazine.org/demonstrating-perl-with-tic-tac-toe-part-3/ [5]: https://en.wikipedia.org/wiki/Deterministic_system [6]: https://perldoc.perl.org/5.32.0/constant.html#TECHNICAL-NOTES [7]: https://perldoc.perl.org/5.8.2/perlretut.html#Compiling-and-saving-regular-expressions [8]: https://perldoc.perl.org/5.8.2/functions/getpwnam.html [9]: https://perldoc.perl.org/perlmod.html#Packages