Recently I saw a thread about when to use a subroutine. It had some useful ideas, but now I want to ask How to Make a SMARTER Subroutine?

In a fit of boredome-turned-educational I wrote this small Tk game: 
#!perl
use warnings;
use strict;
use Tk;
require Tk::ROText;

my $MW=MainWindow->new;
$MW->title("Jump!");
$MW->geometry("775x240+10+10");
my $game_frame=$MW->Frame->pack;

$MW->fontCreate('readable', -family => 'arial', -size => 13);

my $instruct=$game_frame->ROText(    -wrap => "word", 
                     -height => 4, 
                    -font => "readable", 
                    -relief => "flat",
                    -takefocus => 0 )->grid (-row => 0, -columnspan=>1
+3);
$instruct->insert('end', "You've five red and five blue chips. One spa
+ce is blank. Red chips can only move to the right, blue chips to the 
+left. Any chip can move into the blank space. A red chip can jump ove
+r a single blue chip into the blank space. A blue chip can jump over 
+a single red chip into the blank space. Your goal is to get all the r
+eds on the right, and all the blues on the left.");

my @button;
for (1..11) {
  $button[$_]=$game_frame->Button(    -text => "X", 
                    -width => 8, 
                    -height =>4, 
                    -relief => "solid",
                    -activeforeground => "black", 
                    -borderwidth => 3,
                    -command => [ \&move, $_ ] )->
                        grid(-row => 1, -column => $_);
}

$game_frame->Button(    -text => "Start Over",
            -command => [ \&setup ],
            -font => "readable" ) -> grid(-row =>2, -columnspan => 13,
+ -pady => 2);
my $msg;
my $message=$game_frame->Label (-textvariable => \$msg, -font => "read
+able", -foreground => "red") ->
         grid(-row=>3, -columnspan => 13);
setup();

MainLoop;

sub setup {
  $msg="";
  for (1..5) {
    make_color("red", $_);
  }
  for (7..11) {
    make_color("blue", $_);
  }
  make_blank(6);
}

sub make_color {
  my ($c, $index) = @_;
  $button[$index]->configure (    -activebackground => $c,
                -foreground => $c,
                -background => $c,
                -state => "normal");
}

sub make_blank {
  $_=shift;
  $button[$_]->configure (    -background => "white",
                -foreground => "black",
                -activebackground => "white",
                -state => "disabled",
                -disabledforeground => "black");
}

sub move {
  $msg="";
  $_=shift;
  my $old_color = $button[$_]->cget(-background);
  if ($old_color eq "red") {
    if ($_ == 11) {
      alert(1);
    } elsif ($button[$_+1]->cget(-background) eq "red") {
      alert(2);
    } elsif ($_ <= 9 && $button[$_+1]->cget(-background) eq "blue" && 
+$button[$_+2]->cget(-background) ne "white") {
      alert(3);
    } elsif ($button[$_+1]->cget(-background) eq "white") {
      make_color ("red", $_+1);
      make_blank ($_);
      check_win();
    } else {
      make_color ("red", $_+2);
      make_blank ($_);
      check_win();
    }
  }

  if ($old_color eq "blue") {
    if ($_ == 1) {
      alert(1);
    } elsif ($button[$_-1]->cget(-background) eq "blue") {
      alert(2);
    } elsif ($_ >= 2 && $button[$_-1]->cget(-background) eq "red" && $
+button[$_-2]->cget(-background) ne "white") {
      alert(3);
    } elsif ($button[$_-1]->cget(-background) eq "white") {
      make_color ("blue", $_-1);
      make_blank ($_);
      check_win();
    } else {
      make_color ("blue", $_-2);
      make_blank ($_);
      check_win();
    }
  }
}

sub alert {
  $_=shift;
  if ($_ == 1) {
    $msg = "You can't move any further than the end!";
  } elsif ($_ == 2) {
    $msg = "You can't jump over the same color chip!";
  } elsif ($_ == 3) {
    $msg = "You can only jump over the opposite colored chip if the ne
+xt space is blank!";
  } else {
    $msg = "You won!";
    for (1..11) {
      $button[$_]->configure(-state => "disabled");
    }
    for (1..5) {
      $button[$_]->configure(-disabledforeground => "blue");
    }
    $button[6]->configure(-disabledforeground => "white");
    for (7..11) {
      $button[$_]->configure(-disabledforeground => "red");
    }
  }
}

sub check_win {
  for (1..5) {
    if ( $button[$_]->cget(-background) ne "blue" ) {
      return;
    }
  }
  for (7..11) {
    if ( $button[$_]->cget(-background) ne "red" ) {
      return;
    }
  }
  alert(4);
}

[download]
These two if statements look a lot alike:
  if ($old_color eq "red") {
    if ($_ == 11) {
      alert(1);
    } elsif ($button[$_+1]->cget(-background) eq "red") {
      alert(2);
    } elsif ($_ <= 9 && $button[$_+1]->cget(-background) eq "blue" && 
+$button[$_+2]->cget(-background) ne "white") {
      alert(3);
    } elsif ($button[$_+1]->cget(-background) eq "white") {
      make_color ("red", $_+1);
      make_blank ($_);
      check_win();
    } else {
      make_color ("red", $_+2);
      make_blank ($_);
      check_win();
    }
  }

  if ($old_color eq "blue") {
    if ($_ == 1) {
      alert(1);
    } elsif ($button[$_-1]->cget(-background) eq "blue") {
      alert(2);
    } elsif ($_ >= 2 && $button[$_-1]->cget(-background) eq "red" && $
+button[$_-2]->cget(-background) ne "white") {
      alert(3);
    } elsif ($button[$_-1]->cget(-background) eq "white") {
      make_color ("blue", $_-1);
      make_blank ($_);
      check_win();
    } else {
      make_color ("blue", $_-2);
      make_blank ($_);
      check_win();
    }
  }

[download]

and I wish I knew a way to include some toggles to make one sub work for either color, but I'm at a loss how to do that.

When writing a Minesweeper clone I hit something similar:
for $j (1..$row_count) {
    for $k (1..$col_count) {
       #DO SOMETHING, LIKE PLACE RANDOM MINES, 
       #FIGURE OUT WHAT NUMBER GOES HERE, CLEAR
       #ADJACENT EMPTY SPACES, WHATEVER
    }
}

[download]
What I wound up doing was repeating the double-for loop several times in the code. I'd like to be able to do something like: 
sub double_for {
    /&CODE_REFERENCE = $ARG[0];
    for $i (1..$row_count) {
        for $j (1..$col_count) {
            &CODE_REFERENCE($i, $j);
        }
    }
}

[download]
But it's beyond me. It's been said "The Map is Posted on Every Corner" but it's a pretty big map. Any pointers on where to go or where to look?

Thanks and Cheers!
-P
That is what the textbook says, but it's wrong.

-DC

In reply to In Search of a Smarter Sub by Petras

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