Task: Wireworld






PHP: $desc = 'tH.........
.   .
  ........
.   .
Ht.. ......

      ..
tH.... .......
      ..

      ..
tH..... ......
      ..';

$steps = 30;

$world = array(array());
$row = 0;
$col = 0;
foreach(str_split($desc) as $i){
    switch($i){
        case "\n":
            $row++;

            $col = 0;
            $world[] = array();
            break;
        case '.':
            $world[$row][$col] = 1;//conductor
            $col++;
            break;
        case 'H':
            $world[$row][$col] = 2;//head
            $col++;
            break;
        case 't':
            $world[$row][$col] = 3;//tail
            $col++;
            break;
        default:
            $world[$row][$col] = 0;//insulator/air
            $col++;
            break;
    };
};
function draw_world($world){
    foreach($world as $rowc){
        foreach($rowc as $cell){
            switch($cell){
                case 0:
                    echo ' ';
                    break;
                case 1:
                    echo '.';
                    break;
                case 2:
                    echo 'H';
                    break;
                case 3:
                    echo 't';
            };
        };
        echo "\n";
    };

};
echo "Original world:\n";
draw_world($world);
for($i = 0; $i < $steps; $i++){
    $old_world = $world; //backup to look up where was an electron head
    foreach($world as $row => &$rowc){
        foreach($rowc as $col => &$cell){
            switch($cell){
                case 2:
                    $cell = 3;
                    break;
                case 3:
                    $cell = 1;
                    break;
                case 1:
                    $neigh_heads = (int) @$old_world[$row - 1][$col - 1] == 2;
                    $neigh_heads += (int) @$old_world[$row - 1][$col] == 2;
                    $neigh_heads += (int) @$old_world[$row - 1][$col + 1] == 2;
                    $neigh_heads += (int) @$old_world[$row][$col - 1] == 2;
                    $neigh_heads += (int) @$old_world[$row][$col + 1] == 2;
                    $neigh_heads += (int) @$old_world[$row + 1][$col - 1] == 2;
                    $neigh_heads += (int) @$old_world[$row + 1][$col] == 2;
                    if($neigh_heads == 1 || $neigh_heads == 2){
                        $cell = 2;
                    };
            };
        };
        unset($cell); //just to be safe
    };
    unset($rowc); //just to be safe
    echo "\nStep " . ($i + 1) . ":\n";
    draw_world($world);
};


Python: 

from io import StringIO
from collections import namedtuple
from pprint import pprint as pp
import copy

WW = namedtuple('WW', 'world, w, h')
head, tail, conductor, empty = allstates = 'Ht. '


infile = StringIO()

def readfile(f):
    
    world  = [row.rstrip('\r\n') for row in f]
    height = len(world)
    width  = max(len(row) for row in world)
    
    nonrow = [ " %*s " % (-width, "") ]
    world  = nonrow + \
               [ " %*s " % (-width, row) for row in world ] + \
               nonrow   
    world = [list(row) for row in world]
    return WW(world, width, height)

def newcell(currentworld, x, y):
    istate = currentworld[y][x]
    assert istate in allstates, 'Wireworld cell set to unknown value "%s"' % istate
    if istate == head:
        ostate = tail
    elif istate == tail:
        ostate = conductor
    elif istate == empty:
        ostate = empty
    else: 
        n = sum( currentworld[y+dy][x+dx] == head
                 for dx,dy in ( (-1,-1), (-1,+0), (-1,+1),
                                (+0,-1),          (+0,+1),
                                (+1,-1), (+1,+0), (+1,+1) ) )
        ostate = head if 1 <= n <= 2 else conductor
    return ostate

def nextgen(ww):
    'compute next generation of wireworld'
    world, width, height = ww
    newworld = copy.deepcopy(world)
    for x in range(1, width+1):
        for y in range(1, height+1):
            newworld[y][x] = newcell(world, x, y)
    return WW(newworld, width, height)

def world2string(ww):
    return '\n'.join( ''.join(row[1:-1]).rstrip() for row in ww.world[1:-1] )

ww = readfile(infile)
infile.close()

for gen in range(10):
    print ( ("\n%3i " % gen) + '=' * (ww.w-4) + '\n' )
    print ( world2string(ww) )
    ww = nextgen(ww)