Conway's Game of Life

[rje]

Please excuse me if this has already been posted -- I searched Perlmonks for mention of this program, and I was surprised that it's not here (surely it must be here!). IF it is here, then my apologies; and in fact, if 'youse guys' can maybe turn this exercise into a GOLF I think the results might be very cool.

Anyway, I implemented CGoL using the old version 5.6.1 on our Unix boxes, but testing it with PuTTY I see that the `clear` command doesn't seem to work (strange...).

The code initializes the matrix from __DATA__, but you can delete the stuff after __DATA__ and just hand it an input pattern from <>.

One way to speed up this code is to allow two more states, called 'newborn' and 'dying'. Newborns, belonging to a transitional state, are not counted as 'alive' (so there are no spurious additional births), and dying cells can be marked but not yet removed from the board (so they can still contribute toward the overall game state for the current epoch). Finally, once all births and deaths are thus marked, another loop can iterate over the birthlist, setting their states to 'alive', and loop over the deathlist, setting their states to 'dead'. All that to avoid rebuilding the grid each time... is it worth the extra effort?

#!/usr/bin/perl -w
use strict;

=head1 life.pl

   name   : life.pl
   desc   : Conway's Game of Life
   syntax : life.pl [delay]


   SYNTAX

   This script implements CGoL.
   There is one optional runtime argument; namely,
   the delay between iterations ('epochs').
    

   THEORY

   CGoL essentially is a cellular automaton.  The playing 
   grid is a 2D matrix of cells with 2 possible states: 
   alive or dead.  Cell state is dependent upon the 8 
   neighbors adjacent to the cell, and the following three 
   rules:

   (1) A cell with exactly 3 live neighbors becomes alive.
   (2) A live cell with 2 or 3 live neighbors remains alive.
   (3) All other cells die.


   INITIAL GRID

   The starting pattern is specified in the __DATA__ section
   at the end of this script.  If there are no lines after 
   __DATA__, then input is read from stdin.
   
   The length of the first line determines the number of 
   columns in the grid, and of course the number of lines 
   determine the number of rows in the grid.  Initial 'live' 
   cells are denoted by x's; initial dead cells are anything 
   else (internally, dead cells are identified by the space 
   character, but the logic is tailored to treat anything 
   'not-alive' as dead).


   GRID CAVEAT
 
   The grid wraps around.  This means cells on the boundary
   can affect other cells on opposite boundaries.

=cut

my $delay = shift || 1;


my $alive = 'x';
my $dead  = ' ';

my @grid = ();

my $rows = 0;
my $cols = 0;

#
#   Read the grid...
#
my @in = <DATA>;
   @in = <> unless @in;

foreach( @in ) {
   chomp;
   my @cells = split( '', $_ );
   my $col = 0;
   foreach( @cells )
   {
      $grid[ $rows ][ $col ] = $_;
      $col++;
   }   
   $cols = $col if $col > $cols;
   $rows++;
}

#
#   Now fill in the grid...
#
for( my $r=0; $r<$rows; $r++ )
{
   for( my $c=0; $c<$cols; $c++ )
   {
      $grid[ $r ][ $c ] = $dead unless $grid[ $r ][ $c ];
   }
}


print "$rows Rows, $cols Cols\n";
my $epochs = 0;

#
# Now loop forever!
#
{
   `clear`;
   &show;
   $epochs++;
   sleep $delay;
   my @newgrid = &copy( @grid );

   for( my $r=0; $r<$rows; $r++ )
   {
      for( my $c=0; $c<$cols; $c++ )
      {
         my $cell      = $grid[ $r ][ $c ];
         my $neighbors = &countNeighbors( $r, $c );

#         print "($r,$c) $cell => $neighbors\n";

         #
         #  If a cell has exactly 3 live neighbors, 
         #  then this is a live cell.
         #
         $newgrid[ $r ][ $c ] = $alive if $neighbors == 3;

         #
         #  If a cell has 2 or 3 live neighbors,
         #  then this cell remains alive if it is alive.
         #
         next if $neighbors == 2 
              || $neighbors == 3;
 
         #
         # rule: all other cells die.
         #
         $newgrid[ $r ][ $c ] = $dead;
      }
   } 
   @grid = @newgrid;
   redo;
}

sub show
{
   foreach( @grid )
   {
      if ( $_ )
      {
         my @row = @{$_};
         print join( "", @row );
      }
      print "\n";
   }
   my $dashes = '-' x ($cols/2 - length( $epochs ));

   print "$dashes $epochs $dashes\n";
}

sub copy
{
   my @grid = @_;
   my @newgrid = ();
   for( my $r=0; $r<$rows; $r++ )
   {
      for( my $c=0; $c<$cols; $c++ )
      {
         $newgrid[ $r ][ $c ] = $grid[ $r ][ $c ];
      }
   }
   return @newgrid;
}

sub countNeighbors
{
   my ($r, $c) = @_;
   my $count = 0;

   $count += isAlive( $r-1, $c-1 );
   $count += isAlive( $r-1, $c   );
   $count += isAlive( $r-1, $c+1 );

   $count += isAlive( $r,   $c-1 );
   $count += isAlive( $r,   $c+1 );

   $count += isAlive( $r+1, $c-1 );
   $count += isAlive( $r+1, $c   );
   $count += isAlive( $r+1, $c+1 );

   return $count;
}

sub isAlive 
{
   my ($r, $c) = @_;
   return 1 if $grid[ $r ][ $c ] 
            && $grid[ $r ][ $c ] eq $alive;
   return 0;
}


__DATA__
-first row-



     x
    xxx
     x



last row