Langton's ant

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Task
Langton's ant
You are encouraged to solve this task according to the task description, using any language you may know.

Langton's ant models an ant sitting on a plane of cells, all of which are white initially, facing in one of four directions. Each cell can either be black or white. The ant moves according to the color of the cell it is currently sitting in, with the following rules:

  1. If the cell is black, it changes to white and the ant turns left;
  2. If the cell is white, it changes to black and the ant turns right;
  3. The Ant then moves forward to the next cell, and repeat from step 1.

This rather simple ruleset leads to an initially chaotic movement pattern, and after about 10000 steps, a cycle appears where the ant moves steadily away from the starting location in a diagonal corridor about 10 pixels wide. Conceptually the ant can then travel to infinitely far away.

For this task, start the ant near the center of a 100 by 100 field of cells, which is about big enough to contain the initial chaotic part of the movement. Follow the movement rules for the ant, terminate when it moves out of the region, and show the cell colors it leaves behind.

The problem has received some analysis, for more details, please take a look at the Wikipedia article.

Contents

[edit] Ada

with Ada.Text_IO;
 
procedure Langtons_Ant is
 
Size: constant Positive := 100; -- change this to extend the playground
 
subtype Step is Integer range -1 .. +1;
 
procedure Right(N, W: in out Step) is
Tmp: Step := W;
begin
W := - N;
N := Tmp;
end Right;
 
procedure Left(N, W: in out Step) is
begin
for I in 1 .. 3 loop
Right(N, W);
end loop;
end Left;
 
Color_Character: array(Boolean) of Character :=
(False => ' ', True => '#');
 
Is_Black: array (1 .. Size, 1 .. Size) of Boolean :=
(others => (others => False)); -- initially, the world is white;
 
Ant_X, Ant_Y: Natural := Size/2; -- Position of Ant;
Ant_North: Step := 1; Ant_West: Step := 0; -- initially, Ant looks northward
 
Iteration: Positive := 1;
 
begin
loop -- iterate the loop until an exception is raised
if Is_Black(Ant_X, Ant_Y) then
Left(Ant_North, Ant_West);
else
Right(Ant_North, Ant_West);
end if;
Is_Black(Ant_X, Ant_Y) := not Is_Black(Ant_X, Ant_Y);
Ant_X := Ant_X - Ant_North; -- this may raise an exception
Ant_Y := Ant_Y - Ant_West; -- this may raise an exception
Iteration := Iteration + 1;
end loop;
 
exception
when Constraint_Error => -- Ant has left its playground ... now output
for X in 1 .. Size loop
for Y in 1 .. Size loop
Ada.Text_IO.Put(Color_Character(Is_Black(X, Y)));
end loop;
Ada.Text_IO.New_Line;
end loop;
Ada.Text_IO.Put_Line("# Iteration:" & Integer'Image(Iteration));
end Langtons_Ant;
 

Ouptut (to save space, I have removed the all-blank lines):

                                         ##  ############  ##                                       
                                        #  ####          #  ##                                      
                                       ###   ##            ## #                                     
                                       # #  #         #  #    #                                     
                                   ##  ## # #         ###       #                                   
                                ### #  #   #     #     ## ##  ###                                   
                                 # #  ###  ## #### ##   # #  # ##  ##                               
                                 # ### ##  # ##  ### # #     ###   ###                              
                               #     #   ##### # #  ####  #   ### # # #                             
                              ### ##   # ####  ## ## ###### # ### #   #                             
                              # ### # ## # # ## ## ## #   ##### ### ##                              
                                  # #   # ## ###   #   # #  ####    # ##                            
                               #  #         ## ##   #  ##     ## #     ##                           
                              ###   # # ## ###  #  ##     #   ### ##  ## #                          
                             #  ###  ##   ## ##   ###  #    #  ## ####   #                          
                            ###   #   # #  # # #### ##  # ## ###  #     #                           
                           #  ###  # ##    #  # ###  #      ### ## #  #  ##                         
                          ###   #     # ## # ##  ##  ##### ####  #### ##   #                        
                         #  ###  # # #  # ### # # ##      ##   # # #    #   #                       
                        ###   #  ## ###  ## #   ##       #### ####   #      #                       
                       #  ###  # #  #   ##  ########### #  ####  #    #    #                        
                      ###   #  ##      # ####  ##  #########  #  ##    #  ##                        
                     #  ###  # #   ##  # ##   ## ## ### ###   #  # ##  #### #                       
                    ###   #  ##   #  # ###### ## # ## # #    ### ###   ##   #                       
                   #  ###  # #   #     ##### # #####     # #  ## #    ##   #                        
                  ###   #  ##    #     # ## ##### ##  # #   #  #  ## #  #  #                        
                 #  ###  # #     #    #   #### #  ##### ##   ##########   ##                        
                ###   #  ##      # ##   ##   #  #   ####  #   ## #### ##                            
               #  ###  # #        ##### #  ##   ## #   #    # #  #  #  # #                          
              ###   #  ##          ##  ## # # #    ## ## # # ##  #  ##  ##                          
             #  ###  # #                 #  #    # ######## # # ##  #### #                          
            ###   #  ##                  #  #   #       ## ##   #  #  ## #                          
           #  ###  # #                    #  #  #      #  ##  ##   ## ####                          
          ###   #  ##                      ##   #       ##  ##    #   # ###                         
         #  ###  # #                            # ##  ####    #### ### ####                         
        ###   #  ##                              ##  ####    ##  # ## # #  #                        
       #  ###  # #                                ##    ##    ## ### ## #####                       
      ###   #  ##                                                # ## #  ####                       
     #  ###  # #                                                     ## ## ##                       
    ###   #  ##                                                      ##                             
   #  ###  # #                                                     # ##  #### #                     
  ###   #  ##                                                     #  # ###  ###                     
 #  ###  # #                                                      # ## #  #  #                      
###   #  ##                                                        ##      ##                       
   ##  # #                                                          ##                              
##  #  ##                                                                                           
 # # # #                                                                                            
#### ##                                                                                             
# ## #                                                                                              
 ####                                                                                               
  ##                                                                                                
# Iteration: 11656

[edit] Aime

Output png

integer
is_white(list map, integer x, integer y)
{
integer p, w;
data b;
 
b = l_q_data(map, y);
w = b_character(b, x >> 3);
p = 1 << (7 - (x & 7));
b_replace(b, x >> 3, w ^ p);
 
return !(w & p);
}
 
void
ant(integer x, integer y, integer d, list map)
{
while (-1 < x && x < 100 && -1 < y && y < 100) {
if (is_white(map, x, y)) {
d += 3;
d &= 3;
} else {
d += 1;
d &= 3;
}
 
if (d & 1) {
y += (d & 2) - 1;
} else {
x += 1 - (d & 2);
}
}
}
 
integer
main(void)
{
integer i;
file f;
list l;
 
i = 100;
while (i) {
data b;
integer j;
 
i -= 1;
j = 13;
while (j) {
j -= 1;
b_append(b, 0);
}
 
l_l_data(l, -1, b);
}
 
ant(50, 50, 2, l);
 
f_open(f, "ant.pbm", OPEN_CREATE | OPEN_TRUNCATE | OPEN_WRITEONLY, 00644);
 
f_text(f, "P4\n100 100\n");
i = 100;
while (i) {
f_b_post(f, l_q_data(l, -i));
i -= 1;
}
 
return 0;
}

[edit] AutoHotkey

ahk forum: discussion

Works with: AutoHotkey 1.1
(Fixed by just me)
#NoEnv
SetBatchLines, -1
; Directions
Directions := {0: "North", 1: "East", 2: "South", 3: "West"}
; Initialize the plane (set all cells to white)
White := 0xFFFFFF
Plane := []
PW := PH := 100
loop, % PH {
I := A_Index
loop, % PW
Plane[I, A_Index] := White
}
; Let it run
DI := D := 0 ; initial direction
X := Y := 50 ; initial coordinates
while (X > 0) && (X <= PW) && (Y > 0) && (Y <= PH) {
D := (D + ((Plane[X, Y] ^= White) ? 1 : 3)) & 3
if (D & 1)
X += -(D = 3) + (D = 1)
else
Y += -(D = 0) + (D = 2)
}
; Show the result
HBM := CreateDIB(Plane, PW, PH, 400, 400, 0)
Gui, Margin, 0, 0
Gui, Add, Text, x0 y0 w20 h440 Center 0x200, W
Gui, Add, Text, x20 y0 w400 h20 Center 0x200, N
Gui, Add, Picture, x20 y20 w400 h400 0x4E hwndHPIC ; SS_REALSIZECONTROL = 0x40 | SS_BITMAP = 0xE
DllCall("User32.dll\SendMessage", "Ptr", HPIC, "UInt", 0x172, "Ptr", 0, "Ptr", HBM) ; STM_SETIMAGE = 0x172
Gui, Add, Text, xp+5 yp h20 0x200 BackgroundTrans, % "Initial direction: " . Directions[DI]
Gui, Add, Text, x20 y420 w400 h20 Center 0x200, S
Gui, Add, Text, x420 y0 w20 h440 Center 0x200, E
Gui, Show, , Langton's ant (%PW%x%PH%)
Return
 
GuiClose:
ExitApp
 
CreateDIB(PixelArray, PAW, PAH, BMW := 0, BMH := 0, Gradient := 1) { ; SKAN, 01-Apr-2014 / array version by just me
SLL := (PAW * 3) + (PAW & 1)
VarSetCapacity(BMBITS, SLL * PAH, 0)
P := &BMBITS
loop, % PAH {
R := A_Index
loop, % PAW
P := Numput(PixelArray[R, A_Index], P + 0, "UInt") - 1
P += (PAW & 1)
}
HBM := DllCall("Gdi32.dll\CreateBitmap", "Int", PAW, "Int", PAH, "UInt", 1, "UInt", 24, "Ptr", 0, "UPtr")
HBM := DllCall("User32.dll\CopyImage", "Ptr", HBM, "UInt", 0, "Int", 0, "Int", 0, "UInt", 0x2008, "UPtr")
DllCall( "Gdi32.dll\SetBitmapBits", "Ptr", HBM, "UInt", SLL * PAH, "Ptr", &BMBITS)
if (!Gradient)
HBM := DllCall("User32.dll\CopyImage", "Ptr", HBM, "UInt", 0, "Int", 0, "Int", 0, "Int", 8, "UPtr")
return DllCall("User32.dll\CopyImage", "Ptr", HBM, "UInt", 0, "Int", BMW, "Int", BMH, "UInt", 0x200C, "UPtr")
} ; http://ahkscript.org/boards/viewtopic.php?f=6&t=3203

[edit] AutoIt

 
Global $iCountMax = 100000
Global $aFields[100][100][2]
Global $iDelayStep = 10 ; stop between steps in msec
 
Global $aDirection[4][4] = [ _ ; [ direction 0-3 ][ left change x, y, right change x, y ]
[-1, 0, +1, 0], _ ; == direction 0
[ 0, -1, 0, +1], _ ; == direction 1
[+1, 0, -1, 0], _ ; == direction 2
[ 0, +1, 0, -1]] ; == direction 3
 
Global $hGui = GUICreate("Langton's ant", 100*8, 100*8)
GUISetBkColor(0xFFFFFF)
 
For $i = 0 To 99
For $j = 0 To 99
$aFields[$i][$j][0] = GUICtrlCreateLabel('', $j*8, $i*8)
GUICtrlSetColor(-1, 0xFF0000)
$aFields[$i][$j][1] = 0
Next
Next
 
GUISetState()
 
GUICtrlSetData($aFields[49][49][0], '#')
 
Do
Sleep($iDelayStep)
Until Not _SetAnt()
 
Do
Until GUIGetMsg() = -3
 
 
Func _SetAnt()
Local Static $iRowLast = 49, $iColLast = 49, $iCount = 0
Local Static $aCol[2] = [0xFFFFFF,0x000000], $iDirection = 0
Local $iRow, $iCol, $fRight = False
If $iCount = $iCountMax Then Return 0
 
; == get current color
Local $iLastColor = $aFields[$iRowLast][$iColLast][1]
 
; == go to left/right
If $iLastColor = 0 Then $fRight = True
 
; == set the ant to the next field
Local $indexX = 0, $indexY = 1
If $fRight Then
$indexX = 2
$indexY = 3
EndIf
$iRow = $iRowLast + ($aDirection[$iDirection][$indexX])
$iCol = $iColLast + ($aDirection[$iDirection][$indexY])
If $iRow < 0 Or $iRow > 99 Or $iCol < 0 Or $iCol > 99 Then Return 0
GUICtrlSetData($aFields[$iRowLast][$iColLast][0], '')
GUICtrlSetData($aFields[$iRow][$iCol][0], '#')
 
; == direction for next step
If $fRight Then
$iDirection += 1
If $iDirection = 4 Then $iDirection = 0
Else
$iDirection -= 1
If $iDirection = -1 Then $iDirection = 3
EndIf
 
; == change the color of the current field
GUICtrlSetBkColor($aFields[$iRowLast][$iColLast][0], $aCol[(Not $iLastColor)*1])
$aFields[$iRowLast][$iColLast][1] = (Not $iLastColor)*1
 
$iRowLast = $iRow
$iColLast = $iCol
$iCount += 1
WinSetTitle($hGui, '', "Langton's ant [ step: " & StringFormat('%06d', $iCount) & " ]")
Return 1
EndFunc ;==>_SetAnt
 

To see the GUI output, click here. --BugFix (talk) 14:48, 16 November 2013 (UTC)

[edit] BBC BASIC

 
REM Implementation of Langton's ant for Rosetta Code
fieldsize%=100
REM Being pedantic, this will actually result in a field of 101 square,
REM since arrays start at 0, and my implementation allows them to use it
DIM field&(fieldsize%,fieldsize%)  : REM variables with an & suffix are byte variables
x%=fieldsize%/2
y%=fieldsize%/2
d%=0
REPEAT
IF field&(x%,y%)=0 THEN field&(x%,y%)=1:d%-=1 ELSE field&(x%,y%)=0:d%+=1
GCOL 15*field&(x%,y%)
PLOT 69,x%*2,y%*2  :REM for historical reasons there are two "plot points" per pixel
d%=(d%+4) MOD 4  :REM ensure direction is always between 0 and 3
CASE d% OF
WHEN 0:y%+=1
WHEN 1:x%+=1
WHEN 2:y%-=1
WHEN 3:x%-=1
ENDCASE
UNTIL x%>fieldsize% OR x%<0 OR y%>fieldsize% OR y%<0
END
 

[edit] bc

The output function o prints the resulting image (as a PBM image) to stdout. One can either store it into a file or pipe it through an image viewer (e.g. bc langton.bc | display).

define o() {
auto i, j
 
"P1 "
w
h
for (j = 0; j < h; j++) {
for (i = 0; i < w; i++) {
a[j * w + i]
}
}
}
 
define l(w, h, x, y) {
auto a[], d, i, x[], y[]
 
/* d represents one of the four possible directions:
* 0
* ⇑
* 3⇐ ⇒1
* ⇓
* 2
* The arrays x[] and y[] contain the changes to the x and y direction for
* each value of d.
*/
x[1] = 1
x[3] = -1
y[0] = -1
y[2] = 1
 
while (1) {
i = y * w + x
if (a[i] == 0) d += 1 /* turn right if white */
if (a[i] == 1) d -= 1 /* turn left if black */
if (d < 0) d = 3
if (d > 3) d = 0
x += x[d]
y += y[d]
a[i] = 1 - a[i] /* toggle cell colour */
if (x < 0) break
if (x == w) break
if (y < 0) break
if (y == h) break
}
 
o()
}
 
l(100, 100, 50, 50)
quit

[edit] C

Requires ANSI terminal.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
 
int w = 0, h = 0;
unsigned char *pix;
 
void refresh(int x, int y)
{
int i, j, k;
printf("\033[H");
for (i = k = 0; i < h; putchar('\n'), i++)
for (j = 0; j < w; j++, k++)
putchar(pix[k] ? '#' : ' ');
}
 
void walk()
{
int dx = 0, dy = 1, i, k;
int x = w / 2, y = h / 2;
 
pix = calloc(1, w * h);
printf("\033[H\033[J");
 
while (1) {
i = (y * w + x);
if (pix[i]) k = dx, dx = -dy, dy = k;
else k = dy, dy = -dx, dx = k;
 
pix[i] = !pix[i];
printf("\033[%d;%dH%c", y + 1, x + 1, pix[i] ? '#' : ' ');
 
x += dx, y += dy;
 
k = 0;
if (x < 0) {
memmove(pix + 1, pix, w * h - 1);
for (i = 0; i < w * h; i += w) pix[i] = 0;
x++, k = 1;
}
else if (x >= w) {
memmove(pix, pix + 1, w * h - 1);
for (i = w-1; i < w * h; i += w) pix[i] = 0;
x--, k = 1;
}
 
if (y >= h) {
memmove(pix, pix + w, w * (h - 1));
memset(pix + w * (h - 1), 0, w);
y--, k = 1;
}
else if (y < 0) {
memmove(pix + w, pix, w * (h - 1));
memset(pix, 0, w);
y++, k = 1;
}
if (k) refresh(x, y);
printf("\033[%d;%dH\033[31m@\033[m", y + 1, x + 1);
 
fflush(stdout);
usleep(10000);
}
}
 
int main(int c, char **v)
{
if (c > 1) w = atoi(v[1]);
if (c > 2) h = atoi(v[2]);
if (w < 40) w = 40;
if (h < 25) h = 25;
 
walk();
return 0;
}

[edit] C++

LangtonsAnt cpp.png

If you want to see it running infinitely, set the const bool INFINIT_RUN = true

 
#include <windows.h>
#include <string>
 
//--------------------------------------------------------------------------------------------------
using namespace std;
 
//--------------------------------------------------------------------------------------------------
const int BMP_SIZE = 600, CELL_SIZE = 4, GRID_SIZE = BMP_SIZE / CELL_SIZE;
const bool INFINIT_RUN = false;
 
enum cellState { WHITE, BLACK, ANT };
enum facing { NOR, EAS, SOU, WES };
enum state { RUNNING, RESTING };
 
//--------------------------------------------------------------------------------------------------
class myBitmap
{
public:
myBitmap() : pen( NULL ) {}
~myBitmap()
{
DeleteObject( pen );
DeleteDC( hdc );
DeleteObject( bmp );
}
 
bool create( int w, int h )
{
BITMAPINFO bi;
ZeroMemory( &bi, sizeof( bi ) );
 
bi.bmiHeader.biSize = sizeof( bi.bmiHeader );
bi.bmiHeader.biBitCount = sizeof( DWORD ) * 8;
bi.bmiHeader.biCompression = BI_RGB;
bi.bmiHeader.biPlanes = 1;
bi.bmiHeader.biWidth = w;
bi.bmiHeader.biHeight = -h;
 
HDC dc = GetDC( GetConsoleWindow() );
bmp = CreateDIBSection( dc, &bi, DIB_RGB_COLORS, &pBits, NULL, 0 );
if( !bmp ) return false;
 
hdc = CreateCompatibleDC( dc );
SelectObject( hdc, bmp );
ReleaseDC( GetConsoleWindow(), dc );
 
width = w; height = h;
 
return true;
}
 
void clear()
{
ZeroMemory( pBits, width * height * sizeof( DWORD ) );
}
 
void setPenColor( DWORD clr )
{
if( pen ) DeleteObject( pen );
pen = CreatePen( PS_SOLID, 1, clr );
SelectObject( hdc, pen );
}
 
void saveBitmap( string path )
{
BITMAPFILEHEADER fileheader;
BITMAPINFO infoheader;
BITMAP bitmap;
DWORD wb;
 
GetObject( bmp, sizeof( bitmap ), &bitmap );
 
DWORD* dwpBits = new DWORD[bitmap.bmWidth * bitmap.bmHeight];
ZeroMemory( dwpBits, bitmap.bmWidth * bitmap.bmHeight * sizeof( DWORD ) );
ZeroMemory( &infoheader, sizeof( BITMAPINFO ) );
ZeroMemory( &fileheader, sizeof( BITMAPFILEHEADER ) );
 
infoheader.bmiHeader.biBitCount = sizeof( DWORD ) * 8;
infoheader.bmiHeader.biCompression = BI_RGB;
infoheader.bmiHeader.biPlanes = 1;
infoheader.bmiHeader.biSize = sizeof( infoheader.bmiHeader );
infoheader.bmiHeader.biHeight = bitmap.bmHeight;
infoheader.bmiHeader.biWidth = bitmap.bmWidth;
infoheader.bmiHeader.biSizeImage = bitmap.bmWidth * bitmap.bmHeight * sizeof( DWORD );
 
fileheader.bfType = 0x4D42;
fileheader.bfOffBits = sizeof( infoheader.bmiHeader ) + sizeof( BITMAPFILEHEADER );
fileheader.bfSize = fileheader.bfOffBits + infoheader.bmiHeader.biSizeImage;
 
GetDIBits( hdc, bmp, 0, height, ( LPVOID )dwpBits, &infoheader, DIB_RGB_COLORS );
 
HANDLE file = CreateFile( path.c_str(), GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL );
WriteFile( file, &fileheader, sizeof( BITMAPFILEHEADER ), &wb, NULL );
WriteFile( file, &infoheader.bmiHeader, sizeof( infoheader.bmiHeader ), &wb, NULL );
WriteFile( file, dwpBits, bitmap.bmWidth * bitmap.bmHeight * 4, &wb, NULL );
CloseHandle( file );
 
delete [] dwpBits;
}
 
HDC getDC() const { return hdc; }
int getWidth() const { return width; }
int getHeight() const { return height; }
 
private:
HBITMAP bmp;
HDC hdc;
HPEN pen;
void *pBits;
int width, height;
};
//--------------------------------------------------------------------------------------------------
class Ant
{
public:
Ant()
{
_bmp.create( BMP_SIZE, BMP_SIZE );
ZeroMemory( _grid, sizeof( _grid ) );
RED_BRUSH = CreateSolidBrush( 255 );
_antState = RUNNING;
}
 
~Ant()
{
DeleteObject( RED_BRUSH );
}
 
void setPosition( int x, int y )
{
_sx = x; _sy = y;
_facing = WES;
}
 
void mainLoop()
{
switch( _antState )
{
case RUNNING:
simulate();
// fall thru
case RESTING:
display();
}
}
 
void setHWND( HWND hwnd ) { _hwnd = hwnd; }
 
private:
void simulate()
{
switch( _grid[_sx][_sy] )
{
case BLACK:
_grid[_sx][_sy] = WHITE;
if( --_facing < NOR ) _facing = WES;
break;
case WHITE:
_grid[_sx][_sy] = BLACK;
if( ++_facing > WES ) _facing = NOR;
}
switch( _facing )
{
case NOR:
if( --_sy < 0 )
{
if( INFINIT_RUN ) _sy = GRID_SIZE - 1;
else _antState = RESTING;
}
break;
case EAS:
if( ++_sx >= GRID_SIZE )
{
if( INFINIT_RUN ) _sx = 0;
else _antState = RESTING;
}
break;
case SOU:
if( ++_sy >= GRID_SIZE )
{
if( INFINIT_RUN ) _sy = 0;
else _antState = RESTING;
}
break;
case WES:
if( --_sx < 0 )
{
if( INFINIT_RUN ) _sx = GRID_SIZE - 1;
else _antState = RESTING;
}
}
}
 
void display()
{
_bmp.clear();
 
HBRUSH br; RECT rc;
int xx, yy; HDC dc = _bmp.getDC();
 
for( int y = 0; y < GRID_SIZE; y++ )
for( int x = 0; x < GRID_SIZE; x++ )
{
switch( _grid[x][y] )
{
case BLACK: br = static_cast<HBRUSH>( GetStockObject( BLACK_BRUSH ) ); break;
case WHITE: br = static_cast<HBRUSH>( GetStockObject( WHITE_BRUSH ) );
}
if( x == _sx && y == _sy ) br = RED_BRUSH;
 
xx = x * CELL_SIZE; yy = y * CELL_SIZE;
SetRect( &rc, xx, yy, xx + CELL_SIZE, yy + CELL_SIZE );
FillRect( dc, &rc, br );
}
 
HDC wdc = GetDC( _hwnd );
BitBlt( wdc, 0, 0, BMP_SIZE, BMP_SIZE, dc, 0, 0, SRCCOPY );
ReleaseDC( _hwnd, wdc );
}
 
myBitmap _bmp;
HWND _hwnd;
HBRUSH RED_BRUSH;
BYTE _grid[GRID_SIZE][GRID_SIZE];
int _sx, _sy, _facing;
state _antState;
};
//--------------------------------------------------------------------------------------------------
class wnd
{
public:
int wnd::Run( HINSTANCE hInst )
{
_hInst = hInst;
_hwnd = InitAll();
 
_ant.setHWND( _hwnd );
_ant.setPosition( GRID_SIZE / 2, GRID_SIZE / 2 );
 
ShowWindow( _hwnd, SW_SHOW );
UpdateWindow( _hwnd );
 
MSG msg;
ZeroMemory( &msg, sizeof( msg ) );
while( msg.message != WM_QUIT )
{
if( PeekMessage( &msg, NULL, 0, 0, PM_REMOVE ) != 0 )
{
TranslateMessage( &msg );
DispatchMessage( &msg );
}
else
{
_ant.mainLoop();
}
}
return UnregisterClass( "_LANGTONS_ANT_", _hInst );
}
private:
static int WINAPI wnd::WndProc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam )
{
switch( msg )
{
case WM_DESTROY: PostQuitMessage( 0 ); break;
default:
return DefWindowProc( hWnd, msg, wParam, lParam );
}
return 0;
}
 
HWND InitAll()
{
WNDCLASSEX wcex;
ZeroMemory( &wcex, sizeof( wcex ) );
wcex.cbSize = sizeof( WNDCLASSEX );
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = ( WNDPROC )WndProc;
wcex.hInstance = _hInst;
wcex.hCursor = LoadCursor( NULL, IDC_ARROW );
wcex.hbrBackground = ( HBRUSH )( COLOR_WINDOW + 1 );
wcex.lpszClassName = "_LANGTONS_ANT_";
 
RegisterClassEx( &wcex );
 
return CreateWindow( "_LANGTONS_ANT_", ".: Langton's Ant -- PJorente :.", WS_SYSMENU, CW_USEDEFAULT, 0, BMP_SIZE, BMP_SIZE, NULL, NULL, _hInst, NULL );
}
 
HINSTANCE _hInst;
HWND _hwnd;
Ant _ant;
};
//--------------------------------------------------------------------------------------------------
int APIENTRY _tWinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow )
{
wnd myWnd;
return myWnd.Run( hInstance );
}
//--------------------------------------------------------------------------------------------------
 

[edit] C#

using System;
 
namespace LangtonAnt
{
public struct Point
{
public int X;
public int Y;
 
public Point(int x, int y)
{
X = x;
Y = y;
}
}
 
enum Direction
{
North, East, West, South
}
 
public class Langton
{
public readonly bool [,] IsBlack;
private Point _origin;
private Point _antPosition = new Point(0, 0);
public bool OutOfBounds { get; set;}
 
// I don't see any mention of what direction the ant is supposed to start out in
private Direction _antDirection = Direction.East;
 
private readonly Direction[] _leftTurn = new[] { Direction.West, Direction.North, Direction.South, Direction.East };
private readonly Direction[] _rightTurn = new[] { Direction.East, Direction.South, Direction.North, Direction.West };
private readonly int[] _xInc = new[] { 0, 1,-1, 0};
private readonly int[] _yInc = new[] {-1, 0, 0, 1};
 
public Langton(int width, int height, Point origin)
{
_origin = origin;
IsBlack = new bool[width, height];
OutOfBounds = false;
}
 
public Langton(int width, int height) : this(width, height, new Point(width / 2, height / 2)) {}
 
private void MoveAnt()
{
_antPosition.X += _xInc[(int)_antDirection];
_antPosition.Y += _yInc[(int)_antDirection];
}
 
public Point Step()
{
if (OutOfBounds)
{
throw new InvalidOperationException("Trying to step after ant is out of bounds");
}
Point ptCur = new Point(_antPosition.X + _origin.X, _antPosition.Y + _origin.Y);
bool leftTurn = IsBlack[ptCur.X, ptCur.Y];
int iDirection = (int) _antDirection;
_antDirection = leftTurn ? _leftTurn[iDirection] : _rightTurn[iDirection];
IsBlack[ptCur.X, ptCur.Y] = !IsBlack[ptCur.X, ptCur.Y];
MoveAnt();
ptCur = new Point(_antPosition.X + _origin.X, _antPosition.Y + _origin.Y);
OutOfBounds =
ptCur.X < 0 ||
ptCur.X >= IsBlack.GetUpperBound(0) ||
ptCur.Y < 0 ||
ptCur.Y >= IsBlack.GetUpperBound(1);
return _antPosition;
}
}
class Program
{
static void Main()
{
Langton ant = new Langton(100, 100);
 
while (!ant.OutOfBounds) ant.Step();
 
for (int iRow = 0; iRow < 100; iRow++)
{
for (int iCol = 0; iCol < 100; iCol++)
{
Console.Write(ant.IsBlack[iCol, iRow] ? "#" : " ");
}
Console.WriteLine();
}
 
Console.ReadKey();
}
}
}
 

Output:

<Blank lines eliminated for efficiency>                          # #                                                                       
                        ## # #                                                                      
                       # ### ##                                                                     
                      #### ### #                                                                    
                      ##### #  ##                                                                   
                       #   ## ## #                                                                  
                        ###   #  ##                                                                 
                         #   ## ## #                                                                
                          ###   #  ##                                                               
                           #   ## ## #                                                              
                            ###   #  ##                                                             
                             #   ## ## #                                                            
                              ###   #  ##                                                           
                               #   ## ## #                                                          
                                ###   #  ##                                                         
                                 #   ## ## #                                                        
                                  ###   #  ##                                                       
                                   #   ## ## #                                                      
                                    ###   #  ##                                                     
                                     #   ## ## #                                                    
                                      ###   #  ##                                                   
                                       #   ## ## #                                                  
                                        ###   #  ##                                                 
                                         #   ## ## #                                                
                                          ###   #  ##                                               
                                           #   ## ## #                                              
                                            ###   #  ##                                             
                                             #   ## ## #                                            
                                              ###   #  ##                                           
                                               #   ## ## #                                          
                                                ###   #  ##                                         
                                                 #   ## ## #  ##                                    
                                                  ###   #  ##  ##                                   
                                                   #   ## ##  ##   #                                
                                             ####   ###   #   #  ###                                
                                            #    #   #   ## ####   #                                
                                           ###    #   # #      # ## #                               
                                           ###    # ##     # ##  # ##                               
                                            #    #   ## # #     ##                                  
                                            # #      # #####  #   #                                 
                                           #   #####          ## ######                             
                                           ###  ##  # ## # # #   ## # ##                            
                                         ##  # ####### #   #  ###    ## #                           
                                        #  #  ###### ##   #  # ##   #   #                           
                                       #    # # ## #  ###### #######   #                            
                                       # #### ## # ####    ##  ## # ## #                            
                                        #    ####   #  # ###### ##    ###                           
                                           #   # ## # ### #  ##  ##   ###                           
                                              #######    #  ## ## #     #                           
                                      ####  ## ##  #### ## ## ##  #     #                           
                                     #    # #   ### ## ###    # ####    #                           
                                    ###       ### # # #####    # #      #                           
                                    # #   ### #### ## #   ## ### ##     #                           
                                          ## ##  ####    #### # # #     #                           
                                     #    #  ##   ###  ###     ###      #                           
                                     ##   ## ### ####  #      ###   ##  #                           
                                     ## # ####     #   #  # ## ### ##   #                           
                                    #### ##   ## ####  # #  #  #  ###   #                           
                                    # ## ###  # # ## # #     # #     # #                            
                                        # #  #    ## ##  # #  ### ##                                
                                        ## #    #  ##### #    #    #  # #                           
                                       # ## #  #    ## ## #  ###      ###                           
                                     # #   #  #  #  #  ###   ##  ##    #                            
                                    ### # ##### ###### ### ####### # ##                             
                                    # # #    #####   ##  ##### #####                                
                                      #  ##   #      #  # ##  ### ###                               
                                   ####   ##### #########   # #                                     
                              ##    #  #     ### # #   # ###  ###                                   
                             #  #  #### ##   ### ##   ### ##     ##                                 
                            ###    # ## # #####   #    #  #  ## ###                                 
                            # ##### # #   ##  ##     #    #   #  #                                  
                                ###### ####  ## #   #  ##  # # ##                                   
                              ##      # ### ##  ####   #   ###                                      
                               #  # #####  #   # ##   #  #  #                                       
                               ## ### #######     #     # ##                                        
                              # #  ## ##      #   ##    #                                           
                             #  # ####        ###  ##  #                                            
                             # ## ###            ##  ##                                             
                              ##                                                                    
                               ##                                                                   

[edit] Clojure

In keeping with the spirit of Clojure, this program eschews mutable state entirely. Instead, all computation occurs within a single recursive loop whose "variables" are "adjusted" at each iteration, a natural fit for this particular execution model.

(let [bounds (set (range 100))
xs [1 0 -1 0] ys [0 -1 0 1]]
(loop [dir 0 x 50 y 50
grid {[x y] false}]
(if (and (bounds x) (bounds y))
(let [cur (not (grid [x y]))
dir (mod (+ dir (if cur -1 1)) 4)]
(recur dir (+ x (xs dir)) (+ y (ys dir))
(merge grid {[x y] cur})))
(doseq [col (range 100)]
(println
(apply str
(map #(if (grid [% col]) \# \.)
(range 100))))))))

[edit] COBOL

The following program displays the simulation in the console, and a very small font size (~4pt) will be needed to fit it into the window.

Works with: OpenCOBOL
       IDENTIFICATION DIVISION.
PROGRAM-ID. langtons-ant.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
78 Grid-Size VALUE 100.
01 grid-area.
03 grid-x OCCURS Grid-Size TIMES.
05 grid-y OCCURS Grid-Size TIMES.
07 cell-colour PIC X VALUE "W".
88 black VALUE "B".
88 white VALUE "W".
 
01 ant-x PIC 999.
01 ant-y PIC 999.
 
01 ant-direction PIC 9.
88 upward VALUE 0.
88 rightward VALUE 1.
88 downward VALUE 2.
88 leftward VALUE 3.
 
78 Pause-Time-Ns VALUE 10000000.
 
01 display-y PIC 999.
 
78 Black-Background VALUE 0.
78 White-Background VALUE 7.
 
01 i PIC 999.
01 j PIC 999.
 
01 pause PIC X.
 
PROCEDURE DIVISION.
main-line.
DIVIDE Grid-Size BY 2 GIVING ant-x, ant-y
 
PERFORM display-initial-grid
PERFORM UNTIL (ant-x = Grid-Size OR 0)
OR (ant-y = Grid-Size OR 0)
PERFORM step-simulation
CALL "CBL_OC_NANOSLEEP" USING Pause-Time-Ns
END-PERFORM
 
DISPLAY "Press enter to quit." AT LINE 1 COLUMN 1
ACCEPT pause
 
GOBACK
.
step-simulation.
IF black (ant-x, ant-y)
SET white (ant-x, ant-y) TO TRUE
PERFORM display-ant-cell
COMPUTE ant-direction =
FUNCTION MOD(ant-direction + 1, 4)
ELSE
SET black (ant-x, ant-y) TO TRUE
PERFORM display-ant-cell
COMPUTE ant-direction =
FUNCTION MOD(ant-direction - 1, 4)
END-IF
 
EVALUATE TRUE
WHEN upward
ADD 1 TO ant-y
WHEN rightward
ADD 1 TO ant-x
WHEN downward
SUBTRACT 1 FROM ant-y
WHEN leftward
SUBTRACT 1 FROM ant-x
END-EVALUATE
.
display-ant-cell.
SUBTRACT ant-y FROM Grid-Size GIVING display-y
IF black (ant-x, ant-y)
DISPLAY SPACE AT LINE display-y COLUMN ant-x
WITH BACKGROUND-COLOR Black-Background
ELSE
DISPLAY SPACE AT LINE display-y COLUMN ant-x
WITH BACKGROUND-COLOR White-Background
END-IF
.
display-initial-grid.
PERFORM VARYING i FROM 1 BY 1 UNTIL i > Grid-Size
AFTER j FROM 1 BY 1 UNTIL j > Grid-Size
DISPLAY SPACE AT LINE i COLUMN j
WITH BACKGROUND-COLOR White-Background
END-PERFORM
.

[edit] CoffeeScript

 
class Ant
constructor: (@world) ->
@location = [0, 0]
@direction = 'E'
 
move: =>
[x, y] = @location
if @world.is_set x, y
@world.unset x, y
@direction = Directions.left @direction
else
@world.set x, y
@direction = Directions.right @direction
@location = Directions.forward(x, y, @direction)
 
# Model a theoretically infinite 2D world with a hash, allowing squares
# to be black or white (independent of any ants.)
class BlackWhiteWorld
constructor: ->
@bits = {}
 
set: (x, y) ->
@bits["#{x},#{y}"] = true
 
unset: (x, y) ->
delete @bits["#{x},#{y}"]
 
is_set: (x, y) ->
@bits["#{x},#{y}"]
 
draw: ->
# Most of this code just involves finding the extent of the world.
# Always include the origin, even if it's not set.
@min_x = @max_x = @min_y = @max_y = 0
for key of @bits
[xx, yy] = (coord for coord in key.split ',')
x = parseInt xx
y = parseInt yy
@min_x = x if x < @min_x
@max_x = x if x > @max_x
@min_y = y if y < @min_y
@max_y = y if y > @max_y
console.log "top left: #{@min_x}, #{@max_y}, bottom right: #{@max_x}, #{@min_y}"
for y in [@max_y..@min_y] by -1
s = ''
for x in [@min_x..@max_x]
if @bits["#{x},#{y}"]
s += '#'
else
s += '_'
console.log s
 
# Simple code for directions, independent of ants.
Directions =
left: (dir) ->
return 'W' if dir == 'N'
return 'S' if dir == 'W'
return 'E' if dir == 'S'
'N'
 
right: (dir) ->
return 'E' if dir == 'N'
return 'S' if dir == 'E'
return 'W' if dir == 'S'
'N'
 
forward: (x, y, dir) ->
return [x, y+1] if dir == 'N'
return [x, y-1] if dir == 'S'
return [x+1, y] if dir == 'E'
return [x-1, y] if dir == 'W'
 
 
world = new BlackWhiteWorld()
ant = new Ant(world)
for i in [1..11500]
ant.move()
console.log "Ant is at #{ant.location}, direction #{ant.direction}"
world.draw()
 

output

 
> coffee langstons_ant.coffee
Ant is at -24,46, direction W
top left: -25, 47, bottom right: 22, -29
_##__##_________________________________________
##_#####________________________________________
#____##_#_______________________________________
____#_#_##______________________________________
_####_###_#_____________________________________
_#####_#__##____________________________________
__#___##_##_#___________________________________
___###___#__##__________________________________
____#___##_##_#_________________________________
_____###___#__##________________________________
______#___##_##_#_______________________________
_______###___#__##______________________________
________#___##_##_#_____________________________
_________###___#__##____________________________
__________#___##_##_#___________________________
___________###___#__##__________________________
____________#___##_##_#_________________________
_____________###___#__##________________________
______________#___##_##_#_______________________
_______________###___#__##______________________
________________#___##_##_#_____________________
_________________###___#__##____________________
__________________#___##_##_#___________________
___________________###___#__##__________________
____________________#___##_##_#_________________
_____________________###___#__##________________
______________________#___##_##_#_______________
_______________________###___#__##______________
________________________#___##_##_#__##_________
_________________________###___#__##__##________
__________________________#___##_##__##___#_____
____________________####___###___#___#__###_____
___________________#____#___#___##_####___#_____
__________________###____#___#_#______#_##_#____
__________________###____#_##_____#_##__#_##____
___________________#____#___##_#_#_____##_______
___________________#_#______#_#####__#___#______
__________________#___#####__________##_######__
__________________###__##__#_##_#_#_#___##_#_##_
________________##__#_#######_#___#__###____##_#
_______________#__#__######_##___#__#_##___#___#
______________#____#_#_##_#__######_#######___#_
______________#_####_##_#_####____##__##_#_##_#_
_______________#____####___#__#_######_##____###
__________________#___#_##_#_###_#__##__##___###
_____________________#######____#__##_##_#_____#
_____________####__##_##__####_##_##_##__#_____#
____________#____#_#___###_##_###____#_####____#
___________###_______###_#_#_#####____#_#______#
___________#_#___###_####_##_#___##_###_##_____#
_________________##_##__####____####_#_#_#_____#
____________#____#__##___###__###_____###______#
____________##___##_###_####__#______###___##__#
____________##_#_####_____#___#__#_##_###_##___#
___________####_##___##_####__#_#__#__#__###___#
___________#_##_###__#_#_##_#_#_____#_#_____#_#_
_______________#_#__#____##_##__#_#__###_##_____
_______________##_#____#__#####_#____#____#__#_#
______________#_##_#__#____##_##_#__###______###
____________#_#___#__#__#__#__###___##__##____#_
___________###_#_#####_######_###_#######_#_##__
___________#_#_#____#####___##__#####_#####_____
_____________#__##___#______#__#_##__###_###____
__________####___#####_#########___#_#__________
_____##____#__#_____###_#_#___#_###__###________
____#__#__####_##___###_##___###_##_____##______
___###____#_##_#_#####___#____#__#__##_###______
___#_#####_#_#___##__##_____#____#___#__#_______
_______######_####__##_#___#__##__#_#_##________
_____##______#_###_##__####___#___###___________
______#__#_#####__#___#_##___#__#__#____________
______##_###_#######_____#_____#_##_____________
_____#_#__##_##______#___##____#________________
____#__#_####________###__##__#_________________
____#_##_###____________##__##__________________
_____##_________________________________________
______##________________________________________
 


[edit] Common Lisp

(defmacro toggle (gv) `(setf  ,gv (not ,gv)))
 
(defun langtons-ant (width height start-x start-y start-dir)
(let ( (grid (make-array (list width height)))
(x start-x)
(y start-y)
(dir start-dir) )
(loop while (and (< -1 x width) (< -1 y height)) do
(if (toggle (aref grid x y))
(setq dir (mod (1+ dir) 4))
(setq dir (mod (1- dir) 4)))
(case dir
(0 (decf y))
(1 (incf x))
(2 (incf y))
(3 (decf x)))
)
grid
)
)
 
(defun show-grid (grid)
(destructuring-bind (width height) (array-dimensions grid)
(dotimes (y height)
(dotimes (x width)
(princ (if (aref grid x y) "#" ".")))
(princ #\Newline))
)
)
 
(setf *random-state* (make-random-state t))
(show-grid (langtons-ant 100 100 (+ 45 (random 10)) (+ 45 (random 10)) (random 4)))

[edit] D

[edit] Textual Version

void main() {
import std.stdio, std.traits;
 
enum width = 75, height = 52;
enum maxSteps = 12_000;
enum Direction { up, right, down, left }
enum Color : char { white = '.', black = '#' }
uint x = width / 2, y = height / 2;
auto M = new Color[][](height, width);
auto dir = Direction.up;
 
with (Color)
for (int i = 0; i < maxSteps && x < width && y < height; i++) {
immutable turn = M[y][x] == black;
dir = [EnumMembers!Direction][(dir + (turn ? 1 : -1)) & 3];
M[y][x] = (M[y][x] == black) ? white : black;
final switch(dir) with (Direction) {
case up: y--; break;
case right: x--; break;
case down: y++; break;
case left: x++; break;
}
}
 
writefln("%(%-(%c%)\n%)", M);
}
Output:
...........................................................................
...........................................................................
...........................................................................
...........................................................................
.............................##..############..##..........................
............................#..####..........#..##.........................
...........................###...##............##.#........................
...........................#.#..#.........#..#....#........................
.......................##..##.#.#.........###.......#......................
....................###.#..#...#.....#.....##.##..###......................
.....................#.#..###..##.####.##...#.#..#.##..##..................
.....................#.###.##..#.##..###.#.#.....###...###.................
...................#.....#...#####.#.#..####..#...###.#.#.#................
..................###.##...#.####..##.##.######.#.###.#...#................
..................#.###.#.##.#.#.##.##.##.#...#####.###.##.................
......................#.#...#.##.###...#...#.#..####....#.##...............
...................#..#.........##.##...#..##.....##.#.....##..............
..................###...#.#.##.###..#..##.....#...###.##..##.#.............
.................#..###..##...##.##...###..#....#..##.####...#.............
................###...#...#.#..#.#.####.##..#.##.###..#.....#..............
...............#..###..#.##....#..#.###..#......###.##.#..#..##............
..............###...#.....#.##.#.##..##..#####.####..####.##...#...........
.............#..###..#.#.#..#.###.#.#.##......##...#.#.#....#...#..........
............###...#..##.###..##.#...##.......####.####...#......#..........
...........#..###..#.#..#...##..###########.#..####..#....#....#...........
..........###...#..##......#.####..##..#########..#..##....#..##...........
.........#..###..#.#...##..#.##...##.##.###.###...#..#.##..####.#..........
........###...#..##...#..#.######.##.#.##.#.#....###.###...##...#..........
.......#..###..#.#...#.....#####.#.#####.....#.#..##.#....##...#...........
......###...#..##....#.....#.##.#####.##..#.#...#..#..##.#..#..#...........
.....#..###..#.#.....#....#...####.#..#####.##...##########...##...........
....###...#..##......#.##...##...#..#...####..#...##.####.##...............
...#..###..#.#........#####.#..##...##.#...#....#.#..#..#..#.#.............
..###...#..##..........##..##.#.#.#....##.##.#.#.##..#..##..##.............
.#..###..#.#.................#..#....#.########.#.#.##..####.#.............
###...#..##..................#..#...#.......##.##...#..#..##.#.............
...##..#.#....................#..#..#......#..##..##...##.####.............
##..#..##......................##...#.......##..##....#...#.###............
.#.#.#.#............................#.##..####....####.###.####............
####.##..............................##..####....##..#.##.#.#..#...........
#.##.#................................##....##....##.###.##.#####..........
.####................................................#.##.#..####..........
..##.....................................................##.##.##..........
.........................................................##................
.......................................................#.##..####.#........
......................................................#..#.###..###........
......................................................#.##.#..#..#.........
.......................................................##......##..........
........................................................##.................
...........................................................................
...........................................................................
...........................................................................

[edit] Image Version

This similar version requires the module from the Grayscale Image Task to generate and save a PGM image.

import std.stdio, std.algorithm, std.traits, grayscale_image;
 
void main() {
enum width = 100, height = 100;
enum nSteps = 12_000;
enum Direction { up, right, down, left }
auto M = new Image!Gray(width, height);
M.clear(Gray.white);
uint x = width / 2, y = height / 2;
auto dir = Direction.up;
 
for (int i = 0; i < nSteps && x < width && y < height; i++) {
immutable turn = M[x, y] == Gray.black;
dir = [EnumMembers!Direction][(dir + (turn ? 1 : -1)) & 3];
M[x, y] = (M[x, y] == Gray.black) ? Gray.white : Gray.black;
final switch(dir) with (Direction) {
case up: y--; break;
case right: x--; break;
case down: y++; break;
case left: x++; break;
}
}
 
M.savePGM("langton_ant.pgm");
}

[edit] Ela

A straightforward implementation (assumes that we start with ant looking forward):

open list core generic
 
type Field = Field a
type Color = White | Black
type Direction = Lft | Fwd | Rgt | Bwd
field s = Field [[White \\ _ <- [1..s]] \\ _ <- [1..s]]
 
isBlack Black = true
isBlack _ = false
 
newfield xc yc (Field xs) = Field (newfield' 0 xs)
where newfield' _ [] = []
newfield' n (x::xs)
| n == yc = row 0 x :: xs
| else = x :: newfield' (n+1) xs
where row _ [] = []
row n (x::xs)
| n == xc = toggle x :: xs
| else = x :: row (n+1) xs
where toggle White = Black
toggle Black = White
 
showPath (Field xs) = toString <| show' "" xs
where show' sb [] = sb +> ""
show' sb (x::xs) = show' (showRow sb x +> "\r\n") xs
where showRow sb [] = sb +> ""
showRow sb (x::xs) = showRow (sb +> s) xs
where s | isBlack x = "#"
| else = "_"
 
move s xc yc = move' (Fwd,xc,yc) (field s)
where move' (pos,xc,yc)@coor fld
| xc >= s || yc >= s || xc < 0 || yc < 0 = fld
| else = fld |> newfield xc yc |> move' (matrix (dir fld) coor)
where dir (Field xs)
| `isBlack` (xs:yc):xc = Lft
| else = Rgt
matrix Lft (pos,x,y) = go (left pos,x,y)
matrix Rgt (pos,x,y) = go (right pos,x,y)
go (Lft,x,y) = (Lft,x - 1,y)
go (Rgt,x,y) = (Rgt,x+1,y)
go (Fwd,x,y) = (Fwd,x,y - 1)
go (Bwd,x,y) = (Bwd,x,y+1)
right Lft = Fwd
right Fwd = Rgt
right Rgt = Bwd
right Bwd = Lft
left Lft = Bwd
left Bwd = Rgt
left Rgt = Fwd
left Fwd = Lft

This implementation is pure (doesn't produce side effects).

Testing:

showPath <| move 100 50 50

Output (empty lines are skipped to save space):

__________________________________________##__############__##______________________________________
_________________________________________#__####__________#__##_____________________________________
________________________________________###___##____________##_#____________________________________
________________________________________#_#__#_________#__#____#____________________________________
____________________________________##__##_#_#_________###_______#__________________________________
_________________________________###_#__#___#_____#_____##_##__###__________________________________
__________________________________#_#__###__##_####_##___#_#__#_##__##______________________________
__________________________________#_###_##__#_##__###_#_#_____###___###_____________________________
________________________________#_____#___#####_#_#__####__#___###_#_#_#____________________________
_______________________________###_##___#_####__##_##_######_#_###_#___#____________________________
_______________________________#_###_#_##_#_#_##_##_##_#___#####_###_##_____________________________
___________________________________#_#___#_##_###___#___#_#__####____#_##___________________________
________________________________#__#_________##_##___#__##_____##_#_____##__________________________
_______________________________###___#_#_##_###__#__##_____#___###_##__##_#_________________________
______________________________#__###__##___##_##___###__#____#__##_####___#_________________________
_____________________________###___#___#_#__#_#_####_##__#_##_###__#_____#__________________________
____________________________#__###__#_##____#__#_###__#______###_##_#__#__##________________________
___________________________###___#_____#_##_#_##__##__#####_####__####_##___#_______________________
__________________________#__###__#_#_#__#_###_#_#_##______##___#_#_#____#___#______________________
_________________________###___#__##_###__##_#___##_______####_####___#______#______________________
________________________#__###__#_#__#___##__###########_#__####__#____#____#_______________________
_______________________###___#__##______#_####__##__#########__#__##____#__##_______________________
______________________#__###__#_#___##__#_##___##_##_###_###___#__#_##__####_#______________________
_____________________###___#__##___#__#_######_##_#_##_#_#____###_###___##___#______________________
____________________#__###__#_#___#_____#####_#_#####_____#_#__##_#____##___#_______________________
___________________###___#__##____#_____#_##_#####_##__#_#___#__#__##_#__#__#_______________________
__________________#__###__#_#_____#____#___####_#__#####_##___##########___##_______________________
_________________###___#__##______#_##___##___#__#___####__#___##_####_##___________________________
________________#__###__#_#________#####_#__##___##_#___#____#_#__#__#__#_#_________________________
_______________###___#__##__________##__##_#_#_#____##_##_#_#_##__#__##__##_________________________
______________#__###__#_#_________________#__#____#_########_#_#_##__####_#_________________________
_____________###___#__##__________________#__#___#_______##_##___#__#__##_#_________________________
____________#__###__#_#____________________#__#__#______#__##__##___##_####_________________________
___________###___#__##______________________##___#_______##__##____#___#_###________________________
__________#__###__#_#____________________________#_##__####____####_###_####________________________
_________###___#__##______________________________##__####____##__#_##_#_#__#_______________________
________#__###__#_#________________________________##____##____##_###_##_#####______________________
_______###___#__##________________________________________________#_##_#__####______________________
______#__###__#_#_____________________________________________________##_##_##______________________
_____###___#__##______________________________________________________##____________________________
____#__###__#_#_____________________________________________________#_##__####_#____________________
___###___#__##_____________________________________________________#__#_###__###____________________
__#__###__#_#______________________________________________________#_##_#__#__#_____________________
_###___#__##________________________________________________________##______##______________________
#__###__#_#__________________________________________________________##_____________________________
_###_#__##__________________________________________________________________________________________
#_#_#_#_#___________________________________________________________________________________________
_####_##____________________________________________________________________________________________
_#_##_#_____________________________________________________________________________________________
__####______________________________________________________________________________________________
___##_______________________________________________________________________________________________

[edit] Erlang

Over-engineered sine I have summer vacation. Ex: Display function only display lines with black cells.

 
-module( langtons_ant ).
 
-export( [task/0] ).
 
-record( neighbour, {north, south, east, west} ).
-record( state, {colour=white, controller, max_x, max_y, neighbour, position} ).
 
task() ->
Controller = erlang:self(),
Max_x = Max_y = 100,
Pid_positions = plane_create( Controller, Max_x, Max_y ),
Pids = [X || {X, _} <- Pid_positions],
[X ! {pid_positions, Pid_positions} || X <- Pids],
{Pid, _Position} = lists:keyfind( {Max_x div 2, Max_y div 2}, 2, Pid_positions ),
Pid ! {ant_start, north, Controller},
receive
{ant_arrives, _Pid} -> ok
end,
display( Controller, Max_x, Max_y, Pids ),
[X ! {stop, Controller} || X <- Pids].
 
 
 
display( Controller, Max_x, Max_y, Pids ) ->
Positions_colours = display_positions_colours( Pids, Controller ),
All_lines = [display_line( Max_x, Positions_colours, Y ) || Y <- lists:seq(Max_y, 1, -1)],
Lines_with_black = [X || X <- All_lines, lists:member(black, X)],
[io:fwrite( "~s~n", [[display_on_screen(X) || X <- Lines]] ) || Lines <- Lines_with_black].
 
display_line( Max_x, Positions_colours, Y ) -> [proplists:get_value({X,Y}, Positions_colours, white) || X <- lists:seq(1, Max_x)].
 
display_on_screen( white ) -> $_;
display_on_screen( black ) -> $#.
 
display_positions_colours( Pids, Controller ) ->
[X ! {position_colour, Controller} || X <- Pids],
[display_positions_colours_receive() || _X <- Pids].
 
display_positions_colours_receive( ) ->
receive
{position_colour, Position, Colour} -> {Position, Colour}
end.
 
loop( State ) ->
receive
{pid_positions, Pid_positions} ->
{_My_position, Neighbour} = lists:foldl( fun loop_neighbour/2, {State#state.position, #neighbour{}}, Pid_positions ),
erlang:garbage_collect(), % Shrink process after using large Pid_positions. For memory starved systems.
loop( State#state{neighbour=Neighbour} );
{ant_start, Direction, Controller} when Controller =:= State#state.controller ->
{Pid, New_state} = loop_ant_departs( Direction, State ),
Pid ! {ant_arrives, erlang:self()},
loop( New_state );
{ant_arrives, From} ->
{Direction, New_state} = loop_ant_arrives( From, State ),
{To, Newest_state} = loop_ant_departs( Direction, New_state ),
To ! {ant_arrives, erlang:self()},
loop( Newest_state );
{position_colour, Controller} when Controller =:= State#state.controller ->
Controller ! {position_colour, State#state.position, State#state.colour},
loop( State );
{stop, Controller} when Controller =:= State#state.controller -> ok
end.
 
loop_ant_arrives( Pid, State ) ->
Neighbour = State#state.neighbour,
From = loop_ant_arrives_direction( Pid, Neighbour ),
{loop_ant_arrives_new_direction(From, State), State}.
 
loop_ant_arrives_direction( Pid, #neighbour{north=Pid} ) -> north;
loop_ant_arrives_direction( Pid, #neighbour{south=Pid} ) -> south;
loop_ant_arrives_direction( Pid, #neighbour{east=Pid} ) -> east;
loop_ant_arrives_direction( Pid, #neighbour{west=Pid} ) -> west.
 
loop_ant_arrives_new_direction( north, #state{colour=white} ) -> west;
loop_ant_arrives_new_direction( north, #state{colour=black} ) -> east;
loop_ant_arrives_new_direction( south, #state{colour=white} ) -> east;
loop_ant_arrives_new_direction( south, #state{colour=black} ) -> west;
loop_ant_arrives_new_direction( east, #state{colour=white} ) -> north;
loop_ant_arrives_new_direction( east, #state{colour=black} ) -> south;
loop_ant_arrives_new_direction( west, #state{colour=white} ) -> south;
loop_ant_arrives_new_direction( west, #state{colour=black} ) -> north.
 
loop_ant_departs( north, #state{position={_X,Y}, max_y=Y}=State ) ->
{State#state.controller, State};
loop_ant_departs( south, #state{position={_X,1}}=State ) ->
{State#state.controller, State};
loop_ant_departs( east, #state{position={X,_Y}, max_x=X}=State ) ->
{State#state.controller, State};
loop_ant_departs( west, #state{position={1,_Y}}=State ) ->
{State#state.controller, State};
loop_ant_departs( Direction, State ) ->
Neighbour = State#state.neighbour,
Pid = loop_ant_departs_pid( Direction, Neighbour ),
{Pid, State#state{colour=other_colour(State)}}.
 
loop_ant_departs_pid( north, #neighbour{north=Pid} ) -> Pid;
loop_ant_departs_pid( south, #neighbour{south=Pid} ) -> Pid;
loop_ant_departs_pid( east, #neighbour{east=Pid} ) -> Pid;
loop_ant_departs_pid( west, #neighbour{west=Pid} ) -> Pid.
 
loop_neighbour( {Pid, {X, Y}}, {{X, My_y}, Neighbour} ) when Y =:= My_y + 1 -> {{X, My_y}, Neighbour#neighbour{north=Pid}};
loop_neighbour( {Pid, {X, Y}}, {{X, My_y}, Neighbour} ) when Y =:= My_y - 1 -> {{X, My_y}, Neighbour#neighbour{south=Pid}};
loop_neighbour( {Pid, {X, Y}}, {{My_x, Y}, Neighbour} ) when X =:= My_x + 1 -> {{My_x, Y}, Neighbour#neighbour{east=Pid}};
loop_neighbour( {Pid, {X, Y}}, {{My_x, Y}, Neighbour} ) when X =:= My_x - 1 -> {{My_x, Y}, Neighbour#neighbour{west=Pid}};
loop_neighbour( _Pid_position, Acc ) -> Acc.
 
other_colour( #state{colour=white} ) -> black;
other_colour( #state{colour=black} ) -> white.
 
plane_create( Controller, Max_x, Max_y ) -> [{plane_create_cell(Controller, Max_x, Max_y, {X, Y}), {X,Y}} || X <- lists:seq(1, Max_x), Y<- lists:seq(1, Max_y)].
plane_create_cell( Controller, Max_x, Max_y, Position ) -> erlang:spawn_link( fun() -> loop( #state{controller=Controller, max_x=Max_x, max_y=Max_y, position=Position} ) end ).
 
Output:
___________________________________________________________________##_______________________________
____________________________________________________________________##______________________________
_____________________________________________##__##____________###_##_#_____________________________
____________________________________________#__##__###________####_#__#_____________________________
___________________________________________#____##___#______##_##__#_#______________________________
________________________________________##_#_____#_____#######_###_##_______________________________
_______________________________________#__#__#___##_#___#__#####_#__#_______________________________
______________________________________###___#___####__##_###_#______##______________________________
___________________________________##_#_#__##__#___#_##__####_######________________________________
__________________________________#__#___#____#_____##__##___#_#_#####_#____________________________
_________________________________###_##__#__#____#___#####_#_##_#____###____________________________
_________________________________##_____##_###___##_###___##_####__#__#_____________________________
___________________________________###__###_#___#_#_###_____#__#____##______________________________
_____________________________________#_#___#########_#####___####___________________________________
_______________________________###_###__##_#__#______#___##__#______________________________________
________________________________#####_#####__##___#####____#_#_#____________________________________
_____________________________##_#_#######_###_######_#####_#_###____________________________________
____________________________#____##__##___###__#__#__#__#___#_#_____________________________________
___________________________###______###__#_##_##____#__#_##_#_______________________________________
___________________________#_#__#____#____#_#####__#____#_##________________________________________
________________________________##_###__#_#__##_##____#__#_#________________________________________
____________________________#_#_____#_#_____#_#_##_#_#__###_##_#____________________________________
___________________________#___###__#__#__#_#__####_##___##_####____________________________________
___________________________#___##_###_##_#__#___#_____####_#_##_____________________________________
___________________________#__##___###______#__####_###_##___##_____________________________________
___________________________#______###_____###__###___##__#____#_____________________________________
___________________________#_____#_#_#_####____####__##_##__________________________________________
___________________________#_____##_###_##___#_##_####_###___#_#____________________________________
___________________________#______#_#____#####_#_#_###_______###____________________________________
___________________________#____####_#____###_##_###___#_#____#_____________________________________
___________________________#_____#__##_##_##_####__##_##__####______________________________________
___________________________#_____#_##_##__#____#######______________________________________________
___________________________###___##__##__#_###_#_##_#___#___________________________________________
___________________________###____##_######_#__#___####____#________________________________________
____________________________#_##_#_##__##____####_#_##_####_#_______________________________________
____________________________#___#######_######__#_##_#_#____#_______________________________________
___________________________#___#___##_#__#___##_######__#__#________________________________________
___________________________#_##____###__#___#_#######_#__##_________________________________________
____________________________##_#_##___#_#_#_##_#__##__###___________________________________________
_____________________________######_##__________#####___#___________________________________________
_________________________________#___#__#####_#______#_#____________________________________________
__________________________________##_____#_#_##___#____#____________________________________________
_______________________________##_#__##_#_____##_#____###___________________________________________
_______________________________#_##_#______#_#___#____###___________________________________________
________________________________#___####_##___#___#____#____________________________________________
________________________________###__#___#___###___####_____________________________________________
________________________________#___##__##_##___#___________________________________________________
___________________________________##__##__#___###__________________________________________________
____________________________________##__#_##_##___#_________________________________________________
_________________________________________##__#___###________________________________________________
__________________________________________#_##_##___#_______________________________________________
___________________________________________##__#___###______________________________________________
____________________________________________#_##_##___#_____________________________________________
_____________________________________________##__#___###____________________________________________
______________________________________________#_##_##___#___________________________________________
_______________________________________________##__#___###__________________________________________
________________________________________________#_##_##___#_________________________________________
_________________________________________________##__#___###________________________________________
__________________________________________________#_##_##___#_______________________________________
___________________________________________________##__#___###______________________________________
____________________________________________________#_##_##___#_____________________________________
_____________________________________________________##__#___###____________________________________
______________________________________________________#_##_##___#___________________________________
_______________________________________________________##__#___###__________________________________
________________________________________________________#_##_##___#_________________________________
_________________________________________________________##__#___###________________________________
__________________________________________________________#_##_##___#_______________________________
___________________________________________________________##__#___###______________________________
____________________________________________________________#_##_##___#_____________________________
_____________________________________________________________##__#___###____________________________
______________________________________________________________#_##_##___#___________________________
_______________________________________________________________##__#___###__________________________
________________________________________________________________#_##_##___#_________________________
_________________________________________________________________##__#___###________________________
__________________________________________________________________#_##_##___#_______________________
___________________________________________________________________##__#_#####______________________
____________________________________________________________________#_#___####______________________
_____________________________________________________________________##_###_#_______________________
______________________________________________________________________#___##________________________

[edit] Euphoria

Works with: Euphoria version 4.0.3, 4.0.0 RC1 and later
include std\console.e
include std\graphics.e
 
sequence grid = repeat(repeat(1,100),100) --fill 100 by 100 grid with white (1)
sequence antData = {48, 53, 360} --ant x coordinate, y coordinate, facing angle
integer iterations = 0
 
--while ant isn't out of bounds of the 100 by 100 area..
while antData[1] > 0 and antData[1] < 100 and antData[2] > 0 and antData[2] < 100 do
switch grid[antData[1]][antData[2]] do
case 1 then--cell is already white
grid[antData[1]][antData[2]] = 0 --cell turns black, ant turns right
antData[3] += 90
break
case 0 then--cell is already black
grid[antData[1]][antData[2]] = 1 --cell turns white, ant turns left
antData[3] -= 90
break
end switch
--wrap ant directions if > 360 or < 90 (by 90)
switch antData[3] do
case 450 then
antData[3] = 90
break
case 0 then
antData[3] = 360
break
end switch
--move ant based on its new facing, one square
--first north, then south, east, west
switch antData[3] do
case 360 then
antData[2] -= 1
break
case 180 then
antData[2] += 1
break
case 90 then
antData[1] += 1
break
case 270 then
antData[1] -= 1
break
end switch
iterations += 1
end while
 
wrap(0) --don't wrap text output, the grid wouldnt display as a square
 
for y=1 to 100 do
printf(1,"\n")
for x=1 to 100 do
switch grid[x][y] do--each grid block , based on color
case 0 then
printf(1,".")
break
case 1 then
printf(1,"#")
break
end switch
end for
end for
 
printf(1,"\n%d Iterations\n",iterations)
any_key()--wait for keypress, put default message 'press any key..'
SDL output

Code needed to run SDL example with Mark Akita's SDL_gfx_Test1.exw (as template) included with his SDL_gfx package from rapideuphoria.com's archive -

In initialization section :
 
sequence grid = repeat(repeat(1,100),100) --fill 100 by 100 grid with white (1)
sequence antData = {48, 53, 360} --x coordinate, y coordinate, facing angle

In main() , after keystate=SDL_GetKeyState(NULL) , you can adapt the program above to draw the ant's step each frame. Use dummy=pixelColor(surface,x+20,y+12,#000000FF) (for example) to replace the text output. Just before the close of the while loop, use dummy=pixelColor(surface,antData[1]+20,antData[2]+12,#FF0000FF) for the ant and SDL_UpdateRect(surface,0,0,0,0) to display the graphic.

[edit] Fantom

 
class World
{
Int height
Int width
Bool[] state
 
new make (Int height, Int width)
{
this.height = height
this.width = width
state = List(Bool#, height * width)
(height*width).times { state.add (false) }
}
 
Bool inWorld (Int x, Int y)
{
x >= 0 && x < width && y >= 0 && y < height
}
 
Void show ()
{
height.times |h|
{
width.times |w|
{
Env.cur.out.writeChar (state[w*width+h] ? '#' : '.')
}
Env.cur.out.writeChar ('\n')
}
}
 
Void flip (Int x, Int y)
{
state[x*width + y] = !state[x*width + y]
}
 
Bool stateOf (Int x, Int y)
{
state[x*width + y]
}
}
 
enum class Direction
{
up (0, -1),
down (0, 1),
left (-1, 0),
right (1, 0)
 
private new make (Int deltaX, Int deltaY)
{
this.deltaX = deltaX
this.deltaY = deltaY
}
 
Direction rotateLeft ()
{
if (this == up) return left
if (this == down) return right
if (this == left) return down
// if (this == right)
return up
}
 
Direction rotateRight ()
{
if (this == up) return right
if (this == down) return left
if (this == left) return up
// if (this == right)
return down
}
 
const Int deltaX
const Int deltaY
}
 
class Ant
{
World world
Int currX
Int currY
Direction direction
 
new make (World world, Int x, Int y)
{
this.world = world
currX = x
currY = y
direction = Direction.up
}
 
Bool inWorld ()
{
world.inWorld (currX, currY)
}
 
// the ant movement rules
Void move ()
{
if (world.stateOf (currX, currY))
{
direction = direction.rotateLeft
}
else
{
direction = direction.rotateRight
}
world.flip (currX, currY)
currX += direction.deltaX
currY += direction.deltaY
}
}
 
class Main
{
Void main ()
{
world := World (100, 100)
ant := Ant (world, 50, 50)
numIterations := 0
while (ant.inWorld)
{
ant.move
numIterations += 1
}
world.show
echo ("Finished in $numIterations iterations")
}
}
 

Output (snipping the blank lines):

..........................................##..############..##......................................
.........................................#..####..........#..##.....................................
........................................###...##............##.#....................................
........................................#.#..#.........#..#....#....................................
....................................##..##.#.#.........###.......#..................................
.................................###.#..#...#.....#.....##.##..###..................................
..................................#.#..###..##.####.##...#.#..#.##..##..............................
..................................#.###.##..#.##..###.#.#.....###...###.............................
................................#.....#...#####.#.#..####..#...###.#.#.#............................
...............................###.##...#.####..##.##.######.#.###.#...#............................
...............................#.###.#.##.#.#.##.##.##.#...#####.###.##.............................
...................................#.#...#.##.###...#...#.#..####....#.##...........................
................................#..#.........##.##...#..##.....##.#.....##..........................
...............................###...#.#.##.###..#..##.....#...###.##..##.#.........................
..............................#..###..##...##.##...###..#....#..##.####...#.........................
.............................###...#...#.#..#.#.####.##..#.##.###..#.....#..........................
............................#..###..#.##....#..#.###..#......###.##.#..#..##........................
...........................###...#.....#.##.#.##..##..#####.####..####.##...#.......................
..........................#..###..#.#.#..#.###.#.#.##......##...#.#.#....#...#......................
.........................###...#..##.###..##.#...##.......####.####...#......#......................
........................#..###..#.#..#...##..###########.#..####..#....#....#.......................
.......................###...#..##......#.####..##..#########..#..##....#..##.......................
......................#..###..#.#...##..#.##...##.##.###.###...#..#.##..####.#......................
.....................###...#..##...#..#.######.##.#.##.#.#....###.###...##...#......................
....................#..###..#.#...#.....#####.#.#####.....#.#..##.#....##...#.......................
...................###...#..##....#.....#.##.#####.##..#.#...#..#..##.#..#..#.......................
..................#..###..#.#.....#....#...####.#..#####.##...##########...##.......................
.................###...#..##......#.##...##...#..#...####..#...##.####.##...........................
................#..###..#.#........#####.#..##...##.#...#....#.#..#..#..#.#.........................
...............###...#..##..........##..##.#.#.#....##.##.#.#.##..#..##..##.........................
..............#..###..#.#.................#..#....#.########.#.#.##..####.#.........................
.............###...#..##..................#..#...#.......##.##...#..#..##.#.........................
............#..###..#.#....................#..#..#......#..##..##...##.####.........................
...........###...#..##......................##...#.......##..##....#...#.###........................
..........#..###..#.#............................#.##..####....####.###.####........................
.........###...#..##..............................##..####....##..#.##.#.#..#.......................
........#..###..#.#................................##....##....##.###.##.#####......................
.......###...#..##................................................#.##.#..####......................
......#..###..#.#.....................................................##.##.##......................
.....###...#..##......................................................##............................
....#..###..#.#.....................................................#.##..####.#....................
...###...#..##.....................................................#..#.###..###....................
..#..###..#.#......................................................#.##.#..#..#.....................
.###...#..##........................................................##......##......................
#..###..#.#..........................................................##.............................
.###.#..##..........................................................................................
#.#.#.#.#...........................................................................................
.####.##............................................................................................
.#.##.#.............................................................................................
..####..............................................................................................
...##...............................................................................................
Finished in 11669 iterations

[edit] Go

Output png
package main
 
import (
"fmt"
"image"
"image/color"
"image/draw"
"image/png"
"os"
)
 
const (
up = iota
rt
dn
lt
)
 
func main() {
bounds := image.Rect(0, 0, 100, 100)
im := image.NewGray(bounds)
gBlack := color.Gray{0}
gWhite := color.Gray{255}
draw.Draw(im, bounds, image.NewUniform(gWhite), image.ZP, draw.Src)
pos := image.Point{50, 50}
dir := up
for pos.In(bounds) {
switch im.At(pos.X, pos.Y).(color.Gray).Y {
case gBlack.Y:
im.SetGray(pos.X, pos.Y, gWhite)
dir--
case gWhite.Y:
im.SetGray(pos.X, pos.Y, gBlack)
dir++
}
if dir&1 == 1 {
pos.X += 1 - dir&2
} else {
pos.Y -= 1 - dir&2
}
}
f, err := os.Create("ant.png")
if err != nil {
fmt.Println(err)
return
}
if err = png.Encode(f, im); err != nil {
fmt.Println(err)
}
if err = f.Close(); err != nil {
fmt.Println(err)
}
}

[edit] Haskell

data Color = Black | White
deriving (Read, Show, Enum, Eq, Ord)
 
putCell c = putStr (case c of Black -> "#"
White -> ".")
 
toggle :: Color -> Color
toggle color = toEnum $ 1 - fromEnum color
 
 
data Dir = East | North | West | South
deriving (Read, Show, Enum, Eq, Ord)
 
turnLeft South = East
turnLeft dir = succ dir
 
turnRight East = South
turnRight dir = pred dir
 
data Pos = Pos { x :: Int, y :: Int }
deriving (Read)
 
instance Show Pos where
show p@(Pos x y) = "(" ++ (show x) ++ "," ++ (show y) ++ ")"
 
-- Return the new position after moving one unit in the given direction
moveOne pos@(Pos x y) dir =
case dir of
East -> Pos (x+1) y
South -> Pos x (y+1)
West -> Pos (x-1) y
North -> Pos x (y-1)
 
-- Grid is just a list of lists
type Grid = [[Color]]
 
colorAt g p@(Pos x y) = (g !! y) !! x
 
replaceNth n newVal (x:xs)
| n == 0 = newVal:xs
| otherwise = x:replaceNth (n-1) newVal xs
 
toggleCell g p@(Pos x y) =
let newVal = toggle $ colorAt g p
in replaceNth y (replaceNth x newVal (g !! y)) g
 
printRow r = do { mapM_ putCell r ; putStrLn "" }
 
printGrid g = mapM_ printRow g
 
 
data State = State { move :: Int, pos :: Pos, dir :: Dir, grid :: Grid }
 
printState s = do {
putStrLn $ show s;
printGrid $ grid s
}
 
instance Show State where
show s@(State m p@(Pos x y) d g) =
"Move: " ++ (show m) ++ " Pos: " ++ (show p) ++ " Dir: " ++ (show d)
 
nextState s@(State m p@(Pos x y) d g) =
let color = colorAt g p
new_d = case color of White -> (turnRight d)
Black -> (turnLeft d)
new_m = m + 1
new_p = moveOne p new_d
new_g = toggleCell g p
in State new_m new_p new_d new_g
 
inRange size s@(State m p@(Pos x y) d g) =
x >= 0 && x < size && y >= 0 && y < size
 
initialState size = (State 0 (Pos (size`div`2) (size`div`2)) East [ [ White | x <- [1..size] ] | y <- [1..size] ])
 
--- main
size = 100
allStates = initialState size : [nextState s | s <- allStates]
 
main = printState $ last $ takeWhile (inRange size) allStates

[edit] Icon and Unicon

LangtonsAnt unicon 100x100 11655.gif
link graphics,printf
 
procedure main(A)
e := ( 0 < integer(\A[1])) | 100 # 100 or whole number from command line
LangtonsAnt(e)
end
 
record antrec(x,y,nesw)
 
procedure LangtonsAnt(e)
size := sprintf("size=%d,%d",e,e)
label := sprintf("Langton's Ant %dx%d [%d]",e,e,0)
&window := open(label,"g","bg=white",size) |
stop("Unable to open window")
 
ant := antrec(e/2,e/2,?4%4)
board := list(e)
every !board := list(e,"w")
 
k := 0
repeat {
k +:= 1
WAttrib("fg=red")
DrawPoint(ant.x,ant.y)
 
cell := board[ant.x,ant.y]
if cell == "w" then { # white cell
WAttrib("fg=black")
ant.nesw := (ant.nesw + 1) % 4 # . turn right
}
else { # black cell
WAttrib( "fg=white")
ant.nesw := (ant.nesw + 3) % 4 # . turn left = 3 x right
}
board[ant.x,ant.y] := map(cell,"wb","bw") # flip colour
DrawPoint(ant.x,ant.y)
 
case ant.nesw of { # go
0: ant.y -:= 1 # . north
1: ant.x +:= 1 # . east
2: ant.y +:= 1 # . south
3: ant.x -:= 1 # . west
}
 
if 0 < ant.x <= e & 0 < ant.y <= e then next
else break
}
printf("Langton's Ant exited the field after %d rounds.\n",k)
label := sprintf("label=Langton's Ant %dx%d [%d]",e,e,k)
WAttrib(label)
WDone()
end

printf.icn provides formatting graphics.icn provides graphics support (WDone)

[edit] J

dirs=: 0 1,1 0,0 _1,:_1 0
langton=:3 :0
loc=. <.-:$cells=. (_2{.y,y)$dir=. 0
while. *./(0<:loc), loc<$cells do.
color=. (<loc) { cells
cells=. (-.color) (<loc)} cells
dir=. 4 | dir + _1 ^ color
loc=. loc + dir { dirs
end.
' #' {~ cells
)
   langton 100 100
                          # #                                                                       
                        ## # #                                                                      
                       # ### ##                                                                     
                      #### ### #                                                                    
                      ##### #  ##                                                                   
                       #   ## ## #                                                                  
                        ###   #  ##                                                                 
                         #   ## ## #                                                                
                          ###   #  ##                                                               
                           #   ## ## #                                                              
                            ###   #  ##                                                             
                             #   ## ## #                                                            
                              ###   #  ##                                                           
                               #   ## ## #                                                          
                                ###   #  ##                                                         
                                 #   ## ## #                                                        
                                  ###   #  ##                                                       
                                   #   ## ## #                                                      
                                    ###   #  ##                                                     
                                     #   ## ## #                                                    
                                      ###   #  ##                                                   
                                       #   ## ## #                                                  
                                        ###   #  ##                                                 
                                         #   ## ## #                                                
                                          ###   #  ##                                               
                                           #   ## ## #                                              
                                            ###   #  ##                                             
                                             #   ## ## #                                            
                                              ###   #  ##                                           
                                               #   ## ## #                                          
                                                ###   #  ##                                         
                                                 #   ## ## #  ##                                    
                                                  ###   #  ##  ##                                   
                                                   #   ## ##  ##   #                                
                                             ####   ###   #   #  ###                                
                                            #    #   #   ## ####   #                                
                                           ###    #   # #      # ## #                               
                                           ###    # ##     # ##  # ##                               
                                            #    #   ## # #     ##                                  
                                            # #      # #####  #   #                                 
                                           #   #####          ## ######                             
                                           ###  ##  # ## # # #   ## # ##                            
                                         ##  # ####### #   #  ###    ## #                           
                                        #  #  ###### ##   #  # ##   #   #                           
                                       #    # # ## #  ###### #######   #                            
                                       # #### ## # ####    ##  ## # ## #                            
                                        #    ####   #  # ###### ##    ###                           
                                           #   # ## # ### #  ##  ##   ###                           
                                              #######    #  ## ## #     #                           
                                      ####  ## ##  #### ## ## ##  #     #                           
                                     #    # #   ### ## ###    # ####    #                           
                                    ###       ### # # #####    # #      #                           
                                    # #   ### #### ## #   ## ### ##     #                           
                                          ## ##  ####    #### # # #     #                           
                                     #    #  ##   ###  ###     ###      #                           
                                     ##   ## ### ####  #      ###   ##  #                           
                                     ## # ####     #   #  # ## ### ##   #                           
                                    #### ##   ## ####  # #  #  #  ###   #                           
                                    # ## ###  # # ## # #     # #     # #                            
                                        # #  #    ## ##  # #  ### ##                                
                                        ## #    #  ##### #    #    #  # #                           
                                       # ## #  #    ## ## #  ###      ###                           
                                     # #   #  #  #  #  ###   ##  ##    #                            
                                    ### # ##### ###### ### ####### # ##                             
                                    # # #    #####   ##  ##### #####                                
                                      #  ##   #      #  # ##  ### ###                               
                                   ####   ##### #########   # #                                     
                              ##    #  #     ### # #   # ###  ###                                   
                             #  #  #### ##   ### ##   ### ##     ##                                 
                            ###    # ## # #####   #    #  #  ## ###                                 
                            # ##### # #   ##  ##     #    #   #  #                                  
                                ###### ####  ## #   #  ##  # # ##                                   
                              ##      # ### ##  ####   #   ###                                      
                               #  # #####  #   # ##   #  #  #                                       
                               ## ### #######     #     # ##                                        
                              # #  ## ##      #   ##    #                                           
                             #  # ####        ###  ##  #                                            
                             # ## ###            ##  ##                                             
                              ##                                                                    
                               ##                                                                   
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                   

[edit] Java

This implementation allows for sizes other than 100x100, marks the starting position with a green box (sometimes hard to see at smaller zoom levels and the box is smaller than the "pixels" so it doesn't cover up the color of the "pixel" it's in), and includes a "zoom factor" (ZOOM) in case the individual "pixels" are hard to see on your monitor.

import java.awt.Color;
import java.awt.Graphics;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
 
public class Langton extends JFrame{
private JPanel planePanel;
private static final int ZOOM = 4;
 
public Langton(final boolean[][] plane){
planePanel = new JPanel(){
@Override
public void paint(Graphics g) {
for(int y = 0; y < plane.length;y++){
for(int x = 0; x < plane[0].length;x++){
g.setColor(plane[y][x] ? Color.BLACK : Color.WHITE);
g.fillRect(x * ZOOM, y * ZOOM, ZOOM, ZOOM);
}
}
//mark the starting point
g.setColor(Color.GREEN);
g.fillRect(plane[0].length / 2 * ZOOM,
plane.length / 2 * ZOOM, ZOOM/2, ZOOM/2);
}
};
planePanel.setSize(plane[0].length - 1, plane.length - 1);
add(planePanel);
setSize(ZOOM * plane[0].length, ZOOM * plane.length + 30);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
}
 
public static void main(String[] args){
new Langton(runAnt(100, 100));
}
 
private static boolean[][] runAnt(int height, int width){
boolean[][] plane = new boolean[height][width];
int antX = width/2, antY = height/2;//start in the middle-ish
int xChange = 0, yChange = -1; //start moving up
while(antX < width && antY < height && antX >= 0 && antY >= 0){
if(plane[antY][antX]){
//turn left
if(xChange == 0){ //if moving up or down
xChange = yChange;
yChange = 0;
}else{ //if moving left or right
yChange = -xChange;
xChange = 0;
}
}else{
//turn right
if(xChange == 0){ //if moving up or down
xChange = -yChange;
yChange = 0;
}else{ //if moving left or right
yChange = xChange;
xChange = 0;
}
}
plane[antY][antX] = !plane[antY][antX];
antX += xChange;
antY += yChange;
}
return plane;
}
}

Output (click for a larger view):

Langton Java.png

[edit] JavaScript

Utilises the HTML5 canvas element to procedurally generate the image... I wanted to see the progress of the grid state as it was generated, so this implementation produces a incrementally changing image until an 'ant' hits a cell outside of the coordinate system. It can also accept multiple ants, this adds minimal complexity with only the addition of an 'ants' array which is iterated in each step, no additional conditions are necessary to simulate multiple ants, they coexist quite well... good ants ! 1st argument is an array of ant objects, 2nd argument is an object property list of options to change grid size, pixel size and interval (animation speed).

 
// create global canvas
var canvas = document.createElement('canvas');
canvas.id = 'globalCanvas';
document.body.appendChild(canvas);
 
function langtonant(antx, optx) {
'use strict';
var x, y, i;
 
// extend default opts
var opts = {
gridsize: 100,
pixlsize: 4,
interval: 4
};
for (i in optx) {
opts[i] = optx[i];
}
 
// extend default ants
var ants = [{
x: 50,
y: 50,
d: 0
}];
for (i in antx) {
ants[i] = antx[i];
}
 
// initialise grid
var grid = [];
for (x = 0; x < opts.gridsize; x ++) {
grid[x] = [];
for (y = 0; y < opts.gridsize; y ++) {
grid[x][y] = true;
}
}
 
// initialise directions
var dirs = [
{x: 1, y: 0},
{x: 0, y: -1},
{x: -1, y: 0},
{x: 0, y: 1}
];
 
// initialise canvas
var canv = document.getElementById('globalCanvas');
var cont = canv.getContext('2d');
canv.width = opts.gridsize * opts.pixlsize;
canv.height = opts.gridsize * opts.pixlsize;
 
// initialise pixels
var pixlblac = cont.createImageData(opts.pixlsize, opts.pixlsize);
for (i = 0; i < (opts.pixlsize * opts.pixlsize * 4); i += 4) {
pixlblac.data[i + 3] = 255;
}
var pixlwhit = cont.createImageData(opts.pixlsize, opts.pixlsize);
for (i = 0; i < (opts.pixlsize * opts.pixlsize * 4); i += 4) {
pixlwhit.data[i + 3] = 0;
}
 
// run simulation
function simulate() {
var sane = true;
 
// iterate over ants
for (i = 0; i < ants.length; i ++) {
var n = ants[i];
 
// invert, draw, turn
if (grid[n.x][n.y]) {
grid[n.x][n.y] = false;
cont.putImageData(pixlblac, n.x * opts.pixlsize, n.y * opts.pixlsize);
n.d --;
} else {
grid[n.x][n.y] = true;
cont.putImageData(pixlwhit, n.x * opts.pixlsize, n.y * opts.pixlsize);
n.d ++;
}
 
// modulus wraparound
n.d += dirs.length;
n.d %= dirs.length;
 
// position + direction
n.x += dirs[n.d].x;
n.y += dirs[n.d].y;
 
// sanity check
sane = (n.x < 0 || n.x > opts.gridsize || n.y < 0 || n.y > opts.gridsize) ? false : sane;
}
 
// loop with interval
if (sane) {
setTimeout(simulate, opts.interval);
}
}
 
simulate();
}
 

Usage: default ants, custom opts

 
langtonant({}, {
gridsize: 100,
pixlsize: 4,
interval: 4
});
 
Output:

Live Version

Langtons Ant - JavaScript 1.png

Usage: custom ants, default opts

 
langtonant([
{
x: (100 / 2) + 7,
y: (100 / 2) + 7,
d: 1
}, {
x: (100 / 2) + 7,
y: (100 / 2) - 7,
d: 2
}, {
x: (100 / 2) - 7,
y: (100 / 2) - 7,
d: 3
}, {
x: (100 / 2) - 7,
y: (100 / 2) + 7,
d: 0
}
]);
 
Output:

Live Version

Langtons Ant - JavaScript 2.png

[edit] Liberty BASIC

Native graphics. Langtonsant.png

dim arena(100,100)
black=0
white=not(black)
for i = 1 to 100
for j = 1 to 100
arena(i,j)=white
next
next
'north=1 east=2 south=3 west=4
 
nomainwin
graphicbox #1.g, 0, 0, 100, 100
open "Langton's Ant" for window as #1
#1 "trapclose Quit"
#1.g "down"
 
antX=50:antY=50
nsew=1 'ant initially points north
 
while (antX>0) and (antX<100) and (antY>0) and (antY<100)
if arena(antX,antY) then
nsew=nsew-1
if nsew<1 then nsew=4
else
nsew=nsew+1
if nsew>4 then nsew=1
end if
 
select case nsew
case 1: antY=antY-1
case 2: antX=antX+1
case 3: antY=antY+1
case 4: antX=antX-1
end select
 
arena(antX,antY)=not(arena(antX,antY))
#1.g "color ";GetColor$(antX,antY)
#1.g "set ";antX;" ";antY
wend
 
#1.g "flush"
wait
 
function GetColor$(x,y)
if arena(x,y) then
GetColor$="white"
else
GetColor$="black"
end if
end function
 
sub Quit handle$
close #handle$
end
end sub
 

Text version.

 
'move up=1 right=2 down=3 left=4
' ---------------------------------
dim plane(100,100)
x = 50: y = 50
mx = 100
 
while (x>0) and (x<100) and (y>0) and (y<100)
if plane(x,y) then
nxt = nxt - 1
if nxt < 1 then nxt = 4
else
nxt = nxt + 1
if nxt > 4 then nxt = 1
end if
 
x = x + (nxt = 2) - (nxt = 4)
y = y + (nxt = 3) - (nxt = 1)
plane(x,y) = (plane(x,y) <> 1)
mx = min(x,mx)
wend
 
for x = mx to 100
for y = 1 to 100
print chr$((plane(x,y)*3) + 32);
next y
print x
next x
 
 

[edit] Locomotive Basic

10 mode 1:defint a-z:deg
20 ink 1,0:ink 0,26
30 x=50:y=50:ang=270
40 dim play(100,100)
50 graphics pen 3:move 220,100:drawr 200,0:drawr 0,200:drawr -200,0:drawr 0,-200
60 ' move ant
70 if play(x,y) then ang=ang-90 else ang=ang+90
80 play(x,y)=1-play(x,y)
90 plot 220+2*x,100+2*y,play(x,y)
100 ang=ang mod 360
110 x=x+sin(ang)
120 y=y+cos(ang)
130 if x<1 or x>100 or y<1 or y>100 then end
140 goto 70

Output:

Langtons Ant Locomotive BASIC.png

[edit] LOLCODE

HAI 1.3
 
I HAS A plane ITZ A BUKKIT
IM IN YR init UPPIN YR i TIL BOTH SAEM i AN 10000
plane HAS A SRS i ITZ FAIL
IM OUTTA YR init
 
I HAS A x ITZ 50, I HAS A y ITZ 50
I HAS A dir ITZ 0, I HAS A pos, I HAS A cell
 
BTW, WE PURRTIND WE HAS A 2D STRUKSHUR FUR EZ AKSESS
IM IN YR walker
pos R SUM OF PRODUKT OF y AN 100 AN x
cell R NOT plane'Z SRS pos
plane'Z SRS pos R cell
dir R MOD OF SUM OF dir AN SUM OF 5 AN PRODUKT OF cell AN 2 AN 4
 
dir, WTF?
OMG 0, x R SUM OF x AN 1, GTFO
OMG 1, y R DIFF OF y AN 1, GTFO
OMG 2, x R DIFF OF x AN 1, GTFO
OMG 3, y R SUM OF y AN 1, GTFO
OIC
 
BTW, CHEKIN TEH ANTZ BOUNDZ
WON OF BOTH SAEM x AN -1 AN BOTH SAEM x AN 100, O RLY?, YA RLY, GTFO, OIC
WON OF BOTH SAEM y AN -1 AN BOTH SAEM y AN 100, O RLY?, YA RLY, GTFO, OIC
IM OUTTA YR walker
 
IM IN YR printer UPPIN YR cell TIL BOTH SAEM cell AN 10000
plane'Z SRS cell, O RLY?
YA RLY, VISIBLE "#"!
NO WAI, VISIBLE "."!
OIC
 
NOT MOD OF SUM OF cell AN 1 AN 100, O RLY?, YA RLY, VISIBLE "", OIC
IM OUTTA YR printer BTW, UR OUTTA CYAN
 
KTHXBYE

[edit] MATLAB / Octave

function u = langton_ant(n)
if nargin<1, n=100; end;
A = sparse(n,n); % white
P = [n/2;n/2]; % Positon
D = 3; % index of direction 0-3
T = [1,0,-1,0;0,1,0,-1]; % 4 directions
k = 0;
while (1)
k = k+1;
a = A(P(1),P(2));
A(P(1),P(2)) = ~a;
if ( a )
D = mod(D+1,4);
else
D = mod(D-1,4);
end;
P = P+T(:,D+1);
 
if (~mod(k,100)),spy(A);pause(.1);end; %display after every 100 interations
end;
end

[edit] Mathematica

Output
direction = 1;
data = SparseArray[{{50, 50} -> -1}, {100, 100}, 1];
NestWhile[
{Re@#, Im@#} &@(direction *= (data[[Sequence @@ #]] *= -1) I) + # &,
{50, 50}, 1 <= Min@# <= Max@# <= 100 &];
Image@data

[edit] OCaml

open Graphics
 
type dir = North | East | South | West
 
let turn_left = function
| North -> West
| East -> North
| South -> East
| West -> South
 
let turn_right = function
| North -> East
| East -> South
| South -> West
| West -> North
 
let move (x, y) = function
| North -> x, y + 1
| East -> x + 1, y
| South -> x, y - 1
| West -> x - 1, y
 
let () =
open_graph "";
let rec loop (x, y as pos) dir =
let color = point_color x y in
set_color (if color = white then black else white);
plot x y;
let dir = (if color = white then turn_right else turn_left) dir in
if not(key_pressed()) then loop (move pos dir) dir
in
loop (size_x()/2, size_y()/2) North

Run with:

$ ocaml graphics.cma langton.ml

[edit] PARI/GP

Langton-pari.png
langton()={
my(M=matrix(100,100),x=50,y=50,d=0);
while(x && y && x<=100 && y<=100,
d=(d+if(M[x,y],1,-1))%4;
M[x,y]=!M[x,y];
if(d%2,x+=d-2,y+=d-1);
);
M
};
show(M)={
my(d=sum(i=1,#M[,1],sum(j=1,#M,M[i,j])),u=vector(d),v=u,t);
for(i=1,#M[,1],for(j=1,#M,if(M[i,j],v[t++]=i;u[t]=j)));
plothraw(u,v)
};
show(langton())

[edit] Perl

#!/usr/bin/perl
use strict;
# Perl 5 implementation of Langton's Ant
 
# Using screen coordinates - 0,0 in upper-left, +X right, +Y down -
# these directions (right, up, left, down) are counterclockwise
# so advance through the array to turn left, retreat to turn right
my @dirs = ( [1,0], [0,-1], [-1,0], [0,1] );
my $size = 100;
 
# we treat any false as white and true as black, so undef is fine for initial all-white grid
my @plane;
for (0..$size-1) { $plane[$_] = [] };
 
# start out in approximate middle
my ($x, $y) = ($size/2, $size/2);
 
# pointing in a random direction
my $dir = int rand @dirs;
 
my $move;
for ($move = 0; $x >= 0 && $x < $size && $y >= 0 && $y < $size; $move++) {
# toggle cell's value (white->black or black->white)
if ($plane[$x][$y] = 1 - ($plane[$x][$y] ||= 0)) {
# if it's now true (black), then it was white, so turn right
$dir = ($dir - 1) % @dirs;
} else {
# otherwise it was black, so turn left
$dir = ($dir + 1) % @dirs;
}
$x += $dirs[$dir][0];
$y += $dirs[$dir][1];
}
 
print "Out of bounds after $move moves at ($x, $y)\n";
for (my $y=0; $y<$size; ++$y) {
for (my $x=0; $x<$size; ++$x) {
print $plane[$x][$y] ? '#' : '.';
}
print "\n";
}

[edit] Perl 6

Translation of: Perl

In this version we use 4-bits-per-char graphics to shrink the output to a quarter the area of ASCII graphics.

constant @vecs = [1,0,1], [0,-1,1], [-1,0,1], [0,1,1];
constant @blocky = ' ▘▝▀▖▌▞▛▗▚▐▜▄▙▟█'.comb;
constant $size = 100;
enum Square <White Black>;
my @plane = [White xx $size] xx $size;
my ($x, $y) = $size/2, $size/2;
my $dir = @vecs.keys.pick;
my $moves = 0;
loop {
given @plane[$x][$y] {
when :!defined { last }
when White { $dir--; $_ = Black; }
when Black { $dir++; $_ = White; }
}
($x,$y,$moves) »+=« @vecs[$dir %= @vecs];
}
say "Out of bounds after $moves moves at ($x, $y)";
for 0,2,4 ... $size - 2 -> $y {
say join '', gather for 0,2,4 ... $size - 2 -> $x {
take @blocky[ 1 * @plane[$x][$y]
+ 2 * @plane[$x][$y+1]
+ 4 * @plane[$x+1][$y]
+ 8 * @plane[$x+1][$y+1] ];
}
}
Output:
Out of bounds after 11669 moves at (-1, 26)
            ▄▚▚                                   
           ▟▟▜▟▚                                  
           ▜▀▚▌▟▚                                 
            ▜▘▗▌▟▚                                
             ▜▘▗▌▟▚                               
              ▜▘▗▌▟▚                              
               ▜▘▗▌▟▚                             
                ▜▘▗▌▟▚                            
                 ▜▘▗▌▟▚                           
                  ▜▘▗▌▟▚                          
                   ▜▘▗▌▟▚                         
                    ▜▘▗▌▟▚                        
                     ▜▘▗▌▟▚                       
                      ▜▘▗▌▟▚                      
                       ▜▘▗▌▟▚                     
                        ▜▘▗▌▟▚ ▄                  
                         ▜▘▗▌▟▘▟▘▗                
                      ▞▀▚ ▜▘▗▌▄▙▝▜                
                     ▐█  ▌▄▘▘▗▗▞▐▚▌               
                      ▌▖▝ ▐▚▙▙ ▖▀▖                
                     ▐▄▝█▀▖▄▗▗▗▀▐▛▛▙              
                    ▞▚▝▟██▜▞ ▞▗▜▌ ▞▘▌             
                   ▐▗▄▌▙▜▐▄▛▀▜▞▜▛▛▄▐              
                    ▘▗▝▜▚▖▌▟▞▛▜▌▜▖ █▌             
                   ▄▄ ▄▜▛▜▙▖▟▗▛▟▘▌  ▌             
                  ▟▖ ▘▘▄▛▌▛▟█▖ ▚▜▀  ▌             
                  ▘▘ █▚▛▜▟▌▘▗█▞▛▞▌  ▌             
                  ▐▖ ▙▐▙▗█▌▐▀  ▟▛ ▄ ▌             
                  ▟▙▚▛▀▄▗▟▖▐▗▘▛▐▀▟▌ ▌             
                  ▘▀▞▛▗▘▘█▐▞▗▗▝▟▖▄▝▝              
                   ▗▜▞▖▗▘▝█▜▞▖▗▙ ▝ ▙▌             
                  ▟▞▖▟▄▌▟▄▙▐█▗▟▙▟▚▗▞              
                  ▘▌▚▖▝▛▀ ▐▘▞█▀▟▛█▖               
               ▄ ▝▛▚ ▀▜▙▜▜▀▜▚▄▘▙▖                 
              ▟▖▘▐▜▌▛▄▟▛▝▌ ▜▘▛▗▖▟▌                
              ▘▀█▙▙▚▄▛▗▛▖ ▞▗▖▚▗▚▞                 
               ▜ ▖▄▙▛▚▀▗▜▛ ▞▗▝▛                   
               ▞▌▜▌█▀▀▘▖ ▙  ▌▀                    
              ▐▗▌█▛    ▀▚▞▚▞                      
               ▜▖                                 
                                                  

[edit] PicoLisp

Picolisp ant.gif

This code pipes a PBM into ImageMagick's "display" to show the result:

(de ant (Width Height X Y)
(let (Field (make (do Height (link (need Width)))) Dir 0)
(until (or (le0 X) (le0 Y) (> X Width) (> Y Height))
(let Cell (nth Field X Y)
(setq Dir (% (+ (if (car Cell) 1 3) Dir) 4))
(set Cell (not (car Cell)))
(case Dir
(0 (inc 'X))
(1 (inc 'Y))
(2 (dec 'X))
(3 (dec 'Y)) ) ) )
(prinl "P1")
(prinl Width " " Height)
(for Row Field
(prinl (mapcar '[(X) (if X 1 0)] Row)) ) ) )
(out '(display -) (ant 100 100 50 50))
(bye)
 

[edit] PHP

Langtons ant php.png


This is an implementation of Langton`s Ant in PHP
(The TEXT TO IMAGE - part is obviously not necessary.
Additionally the x and y startpositions could be set
to the halves of width and height.)

 
// INIT AND DEFINITION
define('dest_name', 'output.png'); // destination image
define('width', 100);
define('height', 100);
 
$x = 50;
$y = 70;
$dir = 0; // 0-up, 1-left, 2-down, 3-right
$field = array();
$step_count = 0;
 
// LANGTON´S ANT PROCEDURE
while(0 <= $x && $x <= width && 0 <= $y && $y <= height){
if(isset($field[$x][$y])){
unset($field[$x][$y]);
$dir = ($dir + 3) % 4;
}else{
$field[$x][$y] = true;
$dir = ($dir + 1) % 4;
}
switch($dir){
case 0: $y++; break;
case 1: $x--; break;
case 2: $y--; break;
case 3: $x++; break;
}
$step_count++;
}
// ARRAY TO IMAGE
$img = imagecreatetruecolor(width, height);
$white = imagecolorallocate($img, 255, 255, 255);
for($x = 0; $x < width; $x++){
for($y = 0; $y < height; $y++){
if(isset($field[$x][$y])){
imagesetpixel($img, $x, $y, $white);
}
}
}
// TEXT TO IMAGE
$color = array();
$color[0] = imagecolorallocate($img, 255, 0, 0);
$color[1] = imagecolorallocate($img, 0, 255, 0);
$color[2] = imagecolorallocate($img, 0, 0, 255);
$print_array = array(
0 => 'Langton`s Ant', 1=>'PHP Version', 2=>'Steps: ' . $step_count
);
foreach($print_array as $key => $line){
imagestring($img, 3, 3, 3 + $key*11, $line, $color[$key]);
}
// SAVE IMAGE
imagepng($img, dest_name);
 

[edit] Processing

Processing implementation, this uses two notable features of Processing, first of all, the animation is calculated with the draw() loop, second the drawing on the screen is also used to represent the actual state.

/*
* we use the following conventions:
* directions 0: up, 1: left, 2: down: 3: right
*
* pixel white: true, black: false
*
* turn right: true, left: false
*
*/
 
// number of iteration steps per frame
// set this to 1 to see a slow animation of each
// step or to 10 or 100 for a faster animation
 
final int STEP=100;
 
int x;
int y;
int direction;
 
void setup() {
// 100x100 is large enough to show the
// corridor after about 10000 cycles
size(100, 100, P2D);
 
background(#ffffff);
 
x=width/2;
y=height/2;
 
direction=0;
}
 
int count=0;
 
void draw() {
for(int i=0;i<STEP;i++) {
count++;
boolean pix=get(x,y)!=-1; //white =-1
setBool(x,y,pix);
 
turn(pix);
move();
 
if(x<0||y<0||x>=width||y>=height) {
println("finished");
noLoop();
break;
}
}
if(count%1000==0) {
println("iteration "+count);
}
}
 
void move() {
switch(direction) {
case 0:
y--;
break;
case 1:
x--;
break;
case 2:
y++;
break;
case 3:
x++;
break;
}
}
 
void turn(boolean rightleft) {
direction+=rightleft?1:-1;
if(direction==-1) direction=3;
if(direction==4) direction=0;
}
 
void setBool(int x, int y, boolean white) {
set(x,y,white?#ffffff:#000000);
}

[edit] Prolog

This sort of problem, when stated in Prolog, reads a bit like a story book. Our main goal (go) succeeds if we can move north from the middle of the 100x100 matrix, and update_win- which outputs the black/1 blocks. The move/3 and direction/3 goals are really quite self explanatory, mirroring the instructions for the task.

Works with: SWI Prolog version 6.2.6 by Jan Wielemaker, University of Amsterdam
Sample output
%_______________________________________________________________
% Langtons ant.
:-dynamic
black/1.
 
plot_point(Row, Col) :- % Output a 5x5 black box at R,C
new(C, box(5,5)), X is Col * 5 - 2, Y is Row * 5 - 2,
send(C, colour, colour(black)), send(C, fill_pattern, colour(blue)),
send(C, center(point(X,Y))), send(@win, display, C).
update_win :- % Make a 500x500 window, find all the black points and plot them
new(@win, window('Langtons Ant')),
send(@win, size, size(500,500)), send(@win, open),
black(Row/Col),plot_point(Row,Col),fail.
update_win.
 
direction(Row, Col, left) :- black(Row/Col), !, retract(black(Row/Col)).
direction(Row, Col, right):- not(black(Row/Col)), !, assert(black(Row/Col)).
 
move(_, Row,Col) :- (Row < 0; Col < 0; Row > 99; Col > 99), !.
move(north,Row,Col) :-
(direction(Row,Col,left), C is Col - 1, !, move(west, Row, C));
(direction(Row,Col,right), C is Col + 1, !, move(east, Row, C)).
move(south,Row,Col) :-
(direction(Row,Col,right), C is Col - 1, !, move(west, Row, C));
(direction(Row,Col,left), C is Col + 1, !, move(east, Row, C)).
move(east,Row,Col) :-
(direction(Row,Col,right), R is Row + 1, !, move(south, R, Col));
(direction(Row,Col,left), R is Row - 1, !, move(north, R, Col)).
move(west,Row,Col) :-
(direction(Row,Col,left), R is Row + 1, !, move(south, R, Col));
(direction(Row,Col,right), R is Row - 1, !, move(north, R, Col)).
 
go :- retractall(black(_)), move(north,49,49), update_win.

[edit] PureBasic

Sample display of PureBasic solution
#White = $FFFFFF
#Black = 0
#planeHeight = 100
#planeWidth = 100
#canvasID = 0
#windowID = 0
OpenWindow(#windowID, 0, 0, 150, 150, "Langton's ant", #PB_Window_SystemMenu | #PB_Window_ScreenCentered)
CanvasGadget(#canvasID, 25, 25, #planeWidth, #planeHeight)
StartDrawing(CanvasOutput(#canvasID))
Box(0, 0, #planeWidth, #planeHeight, #White)
StopDrawing()
 
Define event, quit, ant.POINT, antDirection, antSteps
 
ant\x = #planeHeight / 2
ant\y = #planeWidth / 2
Repeat
Repeat
event = WindowEvent()
If event = #PB_Event_CloseWindow
quit = 1
event = 0
EndIf
Until event = 0
 
StartDrawing(CanvasOutput(#canvasID))
Select Point(ant\x, ant\y)
Case #Black
Plot(ant\x, ant\y, #White)
antDirection = (antDirection + 1) % 4 ;turn left
Case #White
Plot(ant\x, ant\y, #Black)
antDirection = (antDirection - 1 + 4) % 4 ;turn right
EndSelect
StopDrawing()
 
Select antDirection
Case 0 ;up
ant\y - 1
Case 1 ;left
ant\x - 1
Case 2 ;down
ant\y + 1
Case 3 ;right
ant\x + 1
EndSelect
antSteps + 1
 
If ant\x < 0 Or ant\x >= #planeWidth Or ant\y < 0 Or ant\y >= #planeHeight
MessageRequester("Langton's ant status", "Out of bounds after " + Str(antSteps) + " steps.")
quit = 1
EndIf
 
Delay(10) ;control animation speed and avoid hogging CPU
Until quit = 1

Sample output:

Out of bounds after 11669 steps.

[edit] Python

Translation of: D
width = 75
height = 52
nsteps = 12000
 
class Dir: up, right, down, left = range(4)
class Turn: left, right = False, True
class Color: white, black = '.', '#'
M = [[Color.white] * width for _ in xrange(height)]
 
x = width // 2
y = height // 2
dir = Dir.up
 
i = 0
while i < nsteps and 0 <= x < width and 0 <= y < height:
turn = Turn.left if M[y][x] == Color.black else Turn.right
M[y][x] = Color.white if M[y][x] == Color.black else Color.black
 
dir = (4 + dir + (1 if turn else -1)) % 4
dir = [Dir.up, Dir.right, Dir.down, Dir.left][dir]
if dir == Dir.up: y -= 1
elif dir == Dir.right: x -= 1
elif dir == Dir.down: y += 1
elif dir == Dir.left: x += 1
else: assert False
i += 1
 
print "\n".join("".join(row) for row in M)

The output is the same as the basic D version.

[edit] R

 
langton.ant = function(n = 100) {
map = matrix(data = 0, nrow = n, ncol = n)
p = floor(c(n/2, n/2))
d = sample(1:4, 1)
i = 1
while(p[1] > 0 & p[1] <= n & p[2] > 0 & p[2] <= n) {
if(map[p[1], p[2]] == 1) {
map[p[1], p[2]] = 0
p = p + switch(d, c(0, 1), c(-1, 0), c(0, -1), c(1, 0))
d = ifelse(d == 4, 1, d + 1)
} else {
map[p[1], p[2]] = 1
p = p + switch(d, c(0, -1), c(1, 0), c(0, 1), c(-1, 0))
d = ifelse(d == 1, 4, d - 1)
}
}
return(map)
}
 
image(langton.ant(), xaxt = "n", yaxt = "n", bty = "n")
 

[edit] Racket

Sample display of Racket solution

This Racket program attempts to avoid mutation.

#lang racket
 
;; contracts allow us to describe expected behaviour of funcitons
(define direction/c (or/c 'u 'r 'l 'd))
(define turn/c (-> direction/c direction/c))
(define grid/c (hash/c integer? (hash/c integer? boolean?)))
(define-struct/contract ant ([d direction/c] [x integer?] [y integer?]))
 
(define/contract (turn-right dir) turn/c
(case dir ((u) 'r) ((d) 'l) ((r) 'd) ((l) 'u)))
 
(define/contract (turn-left dir) turn/c
(case dir ((u) 'l) ((d) 'r) ((r) 'u) ((l) 'd)))
 
(define/contract (move d x y)
(-> direction/c integer? integer? (list/c direction/c integer? integer?))
(list
d
(+ x (case d ((l) -1) ((r) 1) (else 0)))
(+ y (case d ((u) -1) ((d) 1) (else 0)))))
 
 
(define/contract (move-ant d a) (-> direction/c ant? ant?)
(apply make-ant (move d (ant-x a) (ant-y a))))
 
(define/contract (langton a grid) (-> ant? grid/c grid/c)
(let ((ax (ant-x a)) (ay (ant-y a)))
(if (and (<= 1 ax 100) (<= 1 ay 100))
(let* ((grid-row (hash-ref grid ay hash))
(cell-black? (hash-ref grid-row ax #f)))
(langton
(move-ant ((if cell-black? turn-left turn-right) (ant-d a)) a)
(hash-set grid ay (hash-set grid-row ax (not cell-black?)))))
grid)))
 
(define/contract (show-grid/text grid) (-> grid/c void?)
(for* ; for* allows us to refer to y in rw
((y (in-range 1 101))
(rw (in-value (hash-ref grid y #f)))
#:when rw  ; if there is no row, the ant never visisted it
#:when (newline) ; when can be used simply for its side effect
(x (in-range 1 101)))
(case (hash-ref rw x #\?)
((#\?) (display #\space)) ; distingush between "ant-visited white" vs. pure white
((#f) (display #\:))  ; little anty footprints left
((#t) (display #\#)))))
 
 
(show-grid/text (langton (make-ant 'u 50 50) (hash)))
 
(require 2htdp/image)
(define/contract (show-grid/png grid) (-> grid/c image?)
(for*/fold
((scn (empty-scene 408 408)))
((y (in-range 1 101))
(rw (in-value (hash-ref grid y #f)))
#:when rw  ; if there is no row, the ant never visisted it
(x (in-range 1 101)))
(case (hash-ref rw x #\?)
((#\?) scn) ; distingush between "ant-visited white" vs. pure white
((#f) (place-image (circle 2 "outline" "gray") (* x 4) (* y 4) scn))  ; little anty footprints left
((#t) (place-image (circle 2 "solid" "black") (* x 4) (* y 4) scn)))))
(show-grid/png (langton (make-ant 'u 50 50) (hash)))
 

Output (text):


                                         ##  ############  ##                                       
                                        #::####::::::::::# :##                                      
                                       ###:::##::::::::::::##:#                                     
                                       #:#::#:::::::::#::#::::#                                     
                                   ##  ##:#:#:::::::::###:::::::#                                   
                                ###:#::#:::#:::::#:::::##:##::###                                   
                                :#:#::###::##:####:##:::#:#::#:##  ##                               
                                :#:###:##: #:##::###:#:#:::::###:::###                              
                               #:::::#:::#####:#:#::####::#:::###:#:#:#                             
                              ###:##:::#:####::##:##:######:#:###:#:::#                             
                              #:###:#:##:#:#:##:##:##:#:::#####:###:##                              
                                ::#:#:::#:##:###:::#:::#:#::####::::# ##                            
                               #::#:::::::::##:##:::#::##:::::##:#::: :##                           
                              ###:::#:#:##:###::#::##:::::#:::###:##::##:#                          
                             #::###::##:::##:##:::###::#::::#::##:####:::#                          
                            ###:::#:::#:#::#:#:####:##::#:##:###::#:::::#                           
                           #::###::#:##::::#::#:###::#::::::###:##:#::#: ##                         
                          ###:::#:::  #:##:#:##::##::#####:####::####:##:::#                        
                         #::###::#:# #::#:###:#:#:##::::::##:::#:#:#::  #:::#                       
                        ###:::#::## ###::##:#:::##:::::::####:####:::#::::::#                       
                       #::###::#:#  #:::##::###########:#::####::#::: #::::#                        
                      ###:::#::##     :#:####::##::#########::#::##::::#::##                        
                     #::###::#:#   ## :#:##:::##:##:###:###:::#::#:##::####:#                       
                    ###:::#::##   #::#:######:##:#:##:#:#::::###:###:::##:::#                       
                   #::###::#:#   #:::::#####:#:#####:::::#:#::##:#::::##:::#                        
                  ###:::#::##    #:::::#:##:#####:##::#:#:::#::#::##:# :#::#                        
                 #::###::#:#     #::::#:::####:#::#####:##:::##########:::##                        
                ###:::#::##      #:##:::##:::#::#:::####::#:::##:####:##:::                         
               #::###::#:#        #####:#::##:::##:#:::#::::#:#::#::#::#:#:                         
              ###:::#::##          ##  ## #:#:#::::##:##:#:#:##::#::##::##:                         
             #::###::#:#                 #::#:   #:########:#:#:##::####:#:                         
            ###:::#::##                  #::#:  #:::::::##:##:::#::#::##:#:                         
           #::###::#:#                    #::#  #::::::#::##::##:::##:####:                         
          ###:::#::##                      ##   #:::::::##::##::::#:::#:###                         
         #::###::#:#                            #:##::####::::####:###:####                         
        ###:::#::##                              ##: ####:   ##: #:##:#:#::#                        
       #::###::#:#                                ##    ##    ## ###:##:#####                       
      ###:::#::##                                                #:##:#::####                       
     #::###::#:#                                                    :##:##:##                       
    ###:::#::##                                                     :##::::::                       
   #::###::#:#                                                     #:##::####:#                     
  ###:::#::##                                                     #::#:###::###                     
 #::###::#:#                                                      #:##:#  #::#                      
###:::#::##                                                        ##:     ##                       
:::##::#:#                                                          ##                              
##::#::##                                                                                           
 #:#:#:#                                                                                            
####:##                                                                                             
#:##:#                                                                                              
 ####                                                                                               
  ##                                                                                                

[edit] REXX

This REXX program automatically justifies (or crops) the left, right, top and bottom of the ant's walk field on the screen.
Or in other words, this REXX program only shows the pertinent part of the ant's walk-field.

/*REXX program implements Langton's ant and displays the path it walked.*/
parse arg dir . /*allow specification: ant facing*/
/*binary colors: 0=white, 1=black*/
@.=0 /*define stem array (all white).*/
lb=1  ; rb=100 /* left boundry, right boundry.*/
bb=1  ; tb=100 /*bottom " top " */
x=(rb-lb)%2 ; y=(tb-bb)%2 /*approximate center (walk start)*/
if dir=='' then dir=random(1,4) /*ant is facing random direction,*/
/*1=north 2=east 3=south 4=west*/
/*───────────────────────────────────────────ant walks hither & thither.*/
do steps=1 until x<lb | x>rb | y<bb | y>tb /*walk until out-of-bounds*/
black=@.x.y /*get color code of ant's cell. */
@.x.y=\@.x.y /*"flip" the color of the cell. */
if black then dir=dir-1 /*if cell was black, turn left. */
else dir=dir+1 /* " " " white, " right. */
if dir==0 then dir=4 /*ant should be facing "west". */
if dir==5 then dir=1 /* " " " " "north". */
select /*ant walks direction it's facing*/
when dir==1 then y=y+1 /*walking north? Then go "up". */
when dir==2 then x=x+1 /* " east? " " "right"*/
when dir==3 then y=y-1 /* " south? " " "down".*/
when dir==4 then x=x-1 /* " west? " " "left".*/
end /*select*/
end /*steps*/
/*───────────────────────────────────────────the ant is finished walking*/
say center(" Langton's ant walked" steps 'steps. ',79,"─"); say
/*Display Langton's ant's trail. */
do minx =lb to rb /*find leftmost non-blank column.*/
do y=bb to tb /*search row by row for it. */
if @.minx.y then leave minx /*found one, now quit searching. */
end /*y*/
end /*minx*/ /*above code crops left of array.*/
 
do y=tb to bb by -1; _='' /*display a plane (row) of cells.*/
do x=minx to rb /*process a "row" of cells. */
_=_ || @.x.y /*build a cell row for display. */
end /*x*/
_=translate(_,'#',10) /*color the cells: black | white.*/
if _\='' then say strip(_,'T') /*say line, strip trailing blanks*/
end /*y*/
/*stick a fork in it, we're done.*/

output

────────────────────── Langton's ant walked 11759 steps. ──────────────────────

                                                                             ##
                                                                            ####
                                                                           # ## #
                                                                          ## ####
                                                                         # # # #
                                                                        ##  #  ##
                                                                       # #  ##
                                                                      ##  #   ###
         ##                                                          # #  ###  #
  ##      ##                                                        ##  #   ###
 #  #  # ## #                                                      # #  ###  #
###  ### #  #                                                     ##  #   ###
# ####  ## #                                                     # #  ###  #
        ##                                                      ##  #   ###
  ## ## ##                                                     # #  ###  #
  ####  # ## #                                                ##  #   ###
  ##### ## ### ##    ##    ##                                # #  ###  #
   #  # # ## #  ##    ####  ##                              ##  #   ###
    #### ### ####    ####  ## #                            # #  ###  #
    ### #   #    ##  ##       #   ##                      ##  #   ###
     #### ##   ##  ##  #      #  #  #                    # #  ###  #
     # ##  #  #   ## ##       #   #  #                  ##  #   ###
     # ####  ## # # ######## #    #  #                 # #  ###  #
     ##  ##  #  ## # # ## ##    # # # ##  ##          ##  #   ###
     # #  #  #  # #    #   # ##   ##  # #####        # #  ###  #
       ## #### ##   #  ####   #  #   ##   ## #      ##  #   ###
   ##   ##########   ## #####  # ####   #    #     # #  ###  #
   #  #  # ##  #  #   # #  ## ##### ## #     #    ##  #   ###
   #   ##    # ##  # #     ##### # #####     #   # #  ###  #
  #   ##   ### ###    # # ## # ## ###### #  #   ##  #   ###
  # ####  ## #  #   ### ### ## ##   ## #  ##   # #  ###  #
   ##  #    ##  #  #########  ##  #### #      ##  #   ###
   #    #    #  ####  # ###########  ##   #  # #  ###  #
  #      #   #### ####       ##   # ##  ### ##  #   ###
  #   #    # # #   ##      ## # # ### #  # # #  ###  #
   #   ## ####  #### #####  ##  ## # ## #     #   ###
    ##  #  # ## ###      #  ### #  #    ## #  ###  #
      #     #  ### ## #  ## #### # #  # #   #   ###
     #   #### ##  #    #  ###   ## ##   ##  ###  #
     # ##  ## ###   #     ##  #  ### ## # #   ###
      ##     # ##     ##  #   ## ##         #  #
       ## #    ####  # #   #   ### ## #   # #
         ## ### #####   # ## ## ## # # ## # ### #
        #   # ### # ###### ## ##  #### #   ## ###
        # # # ###   #  ####  # # #####   #     #
         ###   ###     # # ###  ## #  ## ### #
          ##  ## #  # #   ## #### ##  ###  # #
              ###  ## ##     #     #   #  # ###
              #       ###         # # ##  ##
                #    #  #         #  # #
                # ##            ##   ###
                 ##  #          ####  #
                  ##  ############  ##

[edit] Ruby

class Ant
 
class OutOfBoundsException < StandardError; end
 
class Plane
def initialize(x, y)
@size_x, @size_y = x, y
@cells = Array.new(y) {Array.new(x, :white)}
end
 
def white?(px, py)
@cells[py][px] == :white
end
 
def toggle_colour(px, py)
@cells[py][px] = (white?(px, py) ? :black : :white)
end
 
def check_bounds(px, py)
unless (0 <= px and px < @size_x) and (0 <= py and py < @size_y)
raise OutOfBoundsException, "(#@size_x, #@size_y)"
end
end
 
def to_s
@cells.collect {|row|
row.collect {|cell| cell == :white ? "." : "#"}.join + "\n"
}.join
end
end
 
dir_move = [[:north, [0,-1]], [:east, [1,0]], [:south, [0,1]], [:west, [-1,0]]]
Move = Hash[dir_move]
directions = dir_move.map{|dir, move| dir} # [:north, :east, :south, :west]
Right = Hash[ directions.zip(directions.rotate).to_a ]
Left = Right.invert
 
def initialize(size_x, size_y, pos_x=size_x/2, pos_y=size_y/2)
@plane = Plane.new(size_x, size_y)
@pos_x, @pos_y = pos_x, pos_y
@direction = :south
@plane.check_bounds(@pos_x, @pos_y)
end
 
def run
moves = 0
loop do
begin
moves += 1
move
rescue OutOfBoundsException
break
end
end
moves
end
 
def move
@plane.toggle_colour(@pos_x, @pos_y)
advance
if @plane.white?(@pos_x, @pos_y)
@direction = Right[@direction]
else
@direction = Left[@direction]
end
end
 
def advance
dx, dy = Move[@direction]
@pos_x += dx
@pos_y += dy
@plane.check_bounds(@pos_x, @pos_y)
end
 
def position
"(#@pos_x, #@pos_y)"
end
 
def to_s
@plane.to_s
end
end
 
#
# the simulation
#
ant = Ant.new(100, 100)
moves = ant.run
puts "out of bounds after #{moves} moves: #{ant.position}"
puts ant
Output:
out of bounds after 11669 moves: (26, -1)
..........................#.#.......................................................................
........................##.#.#......................................................................
.......................#.###.##.....................................................................
......................####.###.#....................................................................
......................#####.#..##...................................................................
.......................#...##.##.#..................................................................
........................###...#..##.................................................................
.........................#...##.##.#................................................................
..........................###...#..##...............................................................
...........................#...##.##.#..............................................................
............................###...#..##.............................................................
.............................#...##.##.#............................................................
..............................###...#..##...........................................................
...............................#...##.##.#..........................................................
................................###...#..##.........................................................
.................................#...##.##.#........................................................
..................................###...#..##.......................................................
...................................#...##.##.#......................................................
....................................###...#..##.....................................................
.....................................#...##.##.#....................................................
......................................###...#..##...................................................
.......................................#...##.##.#..................................................
........................................###...#..##.................................................
.........................................#...##.##.#................................................
..........................................###...#..##...............................................
...........................................#...##.##.#..............................................
............................................###...#..##.............................................
.............................................#...##.##.#............................................
..............................................###...#..##...........................................
...............................................#...##.##.#..........................................
................................................###...#..##.........................................
.................................................#...##.##.#..##....................................
..................................................###...#..##..##...................................
...................................................#...##.##..##...#................................
.............................................####...###...#...#..###................................
............................................#....#...#...##.####...#................................
...........................................###....#...#.#......#.##.#...............................
...........................................###....#.##.....#.##..#.##...............................
............................................#....#...##.#.#.....##..................................
............................................#.#......#.#####..#...#.................................
...........................................#...#####..........##.######.............................
...........................................###..##..#.##.#.#.#...##.#.##............................
.........................................##..#.#######.#...#..###....##.#...........................
........................................#..#..######.##...#..#.##...#...#...........................
.......................................#....#.#.##.#..######.#######...#............................
.......................................#.####.##.#.####....##..##.#.##.#............................
........................................#....####...#..#.######.##....###...........................
...........................................#...#.##.#.###.#..##..##...###...........................
..............................................#######....#..##.##.#.....#...........................
......................................####..##.##..####.##.##.##..#.....#...........................
.....................................#....#.#...###.##.###....#.####....#...........................
....................................###.......###.#.#.#####....#.#......#...........................
....................................#.#...###.####.##.#...##.###.##.....#...........................
..........................................##.##..####....####.#.#.#.....#...........................
.....................................#....#..##...###..###.....###......#...........................
.....................................##...##.###.####..#......###...##..#...........................
.....................................##.#.####.....#...#..#.##.###.##...#...........................
....................................####.##...##.####..#.#..#..#..###...#...........................
....................................#.##.###..#.#.##.#.#.....#.#.....#.#............................
........................................#.#..#....##.##..#.#..###.##................................
........................................##.#....#..#####.#....#....#..#.#...........................
.......................................#.##.#..#....##.##.#..###......###...........................
.....................................#.#...#..#..#..#..###...##..##....#............................
....................................###.#.#####.######.###.#######.#.##.............................
....................................#.#.#....#####...##..#####.#####................................
......................................#..##...#......#..#.##..###.###...............................
...................................####...#####.#########...#.#.....................................
..............................##....#..#.....###.#.#...#.###..###...................................
.............................#..#..####.##...###.##...###.##.....##.................................
............................###....#.##.#.#####...#....#..#..##.###.................................
............................#.#####.#.#...##..##.....#....#...#..#..................................
................................######.####..##.#...#..##..#.#.##...................................
..............................##......#.###.##..####...#...###......................................
...............................#..#.#####..#...#.##...#..#..#.......................................
...............................##.###.#######.....#.....#.##........................................
..............................#.#..##.##......#...##....#...........................................
.............................#..#.####........###..##..#............................................
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[edit] Run BASIC

dim plane(100,100)
x = 50: y = 50: minY = 100
 
while (x>0) and (x<100) and (y>0) and (y<100)
if plane(x,y) then
nxt = nxt - 1
if nxt < 1 then nxt = 4
else
nxt = nxt + 1
if nxt > 4 then nxt = 1
end if
 
x = x + (nxt = 2) - (nxt = 4)
y = y + (nxt = 3) - (nxt = 1)
plane(x,y) = (plane(x,y) <> 1)
minY = min(y,minY) ' find lowest and
maxY = max(y,maxY) ' highest y to prevent printing blank lines
wend
 
graphic #g, 100,100
for y = minY to maxY
for x = 1 to 100
print chr$((plane(x,y)*3) + 32);
if plane(x,y) = 1 then #g "color green ; set "; x; " "; y else #g "color blue ; set "; x; " "; y
next x
print y
next y
render #g
#g "flush""
Ouptut (Produces both character and graphic):
graphic
                                                                                                    20
                                                                   ##                               21
                                                                    ##                              22
                                             ##  ##            ### ## #                             23
                                            #  ##  ###        #### #  #                             24
                                           #    ##   #      ## ##  # #                              25
                                        ## #     #     ####### ### ##                               26
                                       #  #  #   ## #   #  ##### #  #                               27
                                      ###   #   ####  ## ### #      ##                              28
                                   ## # #  ##  #   # ##  #### ######                                29
                                  #  #   #    #     ##  ##   # # ##### #                            30
                                 ### ##  #  #    #   ##### # ## #    ###                            31
                                 ##     ## ###   ## ###   ## ####  #  #                             32
                                   ###  ### #   # # ###     #  #    ##                              33
                                     # #   ######### #####   ####                                   34
                               ### ###  ## #  #      #   ##  #                                      35
                                ##### #####  ##   #####    # # #                                    36
                             ## # ####### ### ###### ##### # ###                                    37
                            #    ##  ##   ###  #  #  #  #   # #                                     38
                           ###      ###  # ## ##    #  # ## #                                       39
                           # #  #    #    # #####  #    # ##                                        40
                                ## ###  # #  ## ##    #  # #                                        41
                            # #     # #     # # ## # #  ### ## #                                    42
                           #   ###  #  #  # #  #### ##   ## ####                                    43
                           #   ## ### ## #  #   #     #### # ##                                     44
                           #  ##   ###      #  #### ### ##   ##                                     45
                           #      ###     ###  ###   ##  #    #                                     46
                           #     # # # ####    ####  ## ##                                          47
                           #     ## ### ##   # ## #### ###   # #                                    48
                           #      # #    ##### # # ###       ###                                    49
                           #    #### #    ### ## ###   # #    #                                     50
                           #     #  ## ## ## ####  ## ##  ####                                      51
                           #     # ## ##  #    #######                                              52
                           ###   ##  ##  # ### # ## #   #                                           53
                           ###    ## ###### #  #   ####    #                                        54
                            # ## # ##  ##    #### # ## #### #                                       55
                            #   ####### ######  # ## # #    #                                       56
                           #   #   ## #  #   ## ######  #  #                                        57
                           # ##    ###  #   # ####### #  ##                                         58
                            ## # ##   # # # ## #  ##  ###                                           59
                             ###### ##          #####   #                                           60
                                 #   #  ##### #      # #                                            61
                                  ##     # # ##   #    #                                            62
                               ## #  ## #     ## #    ###                                           63
                               # ## #      # #   #    ###                                           64
                                #   #### ##   #   #    #                                            65
                                ###  #   #   ###   ####                                             66
                                #   ##  ## ##   #                                                   67
                                   ##  ##  #   ###                                                  68
                                    ##  # ## ##   #                                                 69
                                         ##  #   ###                                                70
                                          # ## ##   #                                               71
                                           ##  #   ###                                              72
                                            # ## ##   #                                             73
                                             ##  #   ###                                            74
                                              # ## ##   #                                           75
                                               ##  #   ###                                          76
                                                # ## ##   #                                         77
                                                 ##  #   ###                                        78
                                                  # ## ##   #                                       79
                                                   ##  #   ###                                      80
                                                    # ## ##   #                                     81
                                                     ##  #   ###                                    82
                                                      # ## ##   #                                   83
                                                       ##  #   ###                                  84
                                                        # ## ##   #                                 85
                                                         ##  #   ###                                86
                                                          # ## ##   #                               87
                                                           ##  #   ###                              88
                                                            # ## ##   #                             89
                                                             ##  #   ###                            90
                                                              # ## ##   #                           91
                                                               ##  #   ###                          92
                                                                # ## ##   #                         93
                                                                 ##  #   ###                        94
                                                                  # ## ##   #                       95
                                                                   ##  # #####                      96
                                                                    # #   ####                      97
                                                                     ## ### #                       98
                                                                      # # ##                        99
                                                                                                    100

[edit] Scala

class Langton(matrix:Array[Array[Char]], ant:Ant) {
import Langton._
val rows=matrix.size
val cols=matrix(0).size
 
def isValid = 0 <= ant.row && ant.row < cols && 0 <= ant.col && ant.col < rows
def isBlack=matrix(ant.row)(ant.col)==BLACK
def changeColor(c:Char)={matrix(ant.row)(ant.col)=c; matrix}
 
def evolve():Langton={
val (newCol, newAnt)=if(isBlack) (WHITE, ant.turnLeft) else (BLACK, ant.turnRight)
new Langton(changeColor(newCol), newAnt.move)
}
override def toString()=matrix map (_.mkString("")) mkString "\n"
}
 
case class Ant(row:Int, col:Int, d:Int=0) {
def turnLeft=Ant(row,col,(d-1)&3)
def turnRight=Ant(row,col,(d+1)&3)
def move=d match {
case 0 => Ant(row-1,col,d) // north
case 1 => Ant(row,col+1,d) // east
case 2 => Ant(row+1,col,d) // south
case 3 => Ant(row,col-1,d) // west
}
}
 
object Langton {
val BLACK='#'
val WHITE='.'
def apply(x:Int=100, y:Int=100)=new Langton(Array.fill(y, x)(WHITE), Ant(x>>>1, y>>>1, 0))
 
def main(args: Array[String]): Unit = {
var l=Langton(100,100)
var moves=0
while (l.isValid) {
moves += 1
l=l.evolve
}
println("Out of bounds after "+moves+" moves")
println(l)
}
}

Output:

Out of bounds after 11669 moves
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..........................................##..############..##......................................
.........................................#..####..........#..##.....................................
........................................###...##............##.#....................................
........................................#.#..#.........#..#....#....................................
....................................##..##.#.#.........###.......#..................................
.................................###.#..#...#.....#.....##.##..###..................................
..................................#.#..###..##.####.##...#.#..#.##..##..............................
..................................#.###.##..#.##..###.#.#.....###...###.............................
................................#.....#...#####.#.#..####..#...###.#.#.#............................
...............................###.##...#.####..##.##.######.#.###.#...#............................
...............................#.###.#.##.#.#.##.##.##.#...#####.###.##.............................
...................................#.#...#.##.###...#...#.#..####....#.##...........................
................................#..#.........##.##...#..##.....##.#.....##..........................
...............................###...#.#.##.###..#..##.....#...###.##..##.#.........................
..............................#..###..##...##.##...###..#....#..##.####...#.........................
.............................###...#...#.#..#.#.####.##..#.##.###..#.....#..........................
............................#..###..#.##....#..#.###..#......###.##.#..#..##........................
...........................###...#.....#.##.#.##..##..#####.####..####.##...#.......................
..........................#..###..#.#.#..#.###.#.#.##......##...#.#.#....#...#......................
.........................###...#..##.###..##.#...##.......####.####...#......#......................
........................#..###..#.#..#...##..###########.#..####..#....#....#.......................
.......................###...#..##......#.####..##..#########..#..##....#..##.......................
......................#..###..#.#...##..#.##...##.##.###.###...#..#.##..####.#......................
.....................###...#..##...#..#.######.##.#.##.#.#....###.###...##...#......................
....................#..###..#.#...#.....#####.#.#####.....#.#..##.#....##...#.......................
...................###...#..##....#.....#.##.#####.##..#.#...#..#..##.#..#..#.......................
..................#..###..#.#.....#....#...####.#..#####.##...##########...##.......................
.................###...#..##......#.##...##...#..#...####..#...##.####.##...........................
................#..###..#.#........#####.#..##...##.#...#....#.#..#..#..#.#.........................
...............###...#..##..........##..##.#.#.#....##.##.#.#.##..#..##..##.........................
..............#..###..#.#.................#..#....#.########.#.#.##..####.#.........................
.............###...#..##..................#..#...#.......##.##...#..#..##.#.........................
............#..###..#.#....................#..#..#......#..##..##...##.####.........................
...........###...#..##......................##...#.......##..##....#...#.###........................
..........#..###..#.#............................#.##..####....####.###.####........................
.........###...#..##..............................##..####....##..#.##.#.#..#.......................
........#..###..#.#................................##....##....##.###.##.#####......................
.......###...#..##................................................#.##.#..####......................
......#..###..#.#.....................................................##.##.##......................
.....###...#..##......................................................##............................
....#..###..#.#.....................................................#.##..####.#....................
...###...#..##.....................................................#..#.###..###....................
..#..###..#.#......................................................#.##.#..#..#.....................
.###...#..##........................................................##......##......................
#..###..#.#..........................................................##.............................
.###.#..##..........................................................................................
#.#.#.#.#...........................................................................................
.####.##............................................................................................
.#.##.#.............................................................................................
..####..............................................................................................
...##...............................................................................................
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[edit] Tcl

Library: Tk
Output of Tcl solution of Langton's ant task
package require Tk
 
proc step {workarea} {
global x y dir
if {[lindex [$workarea get $x $y] 0]} {
$workarea put black -to $x $y
if {[incr dir] > 3} {set dir 0}
} else {
$workarea put white -to $x $y
if {[incr dir -1] < 0} {set dir 3}
}
switch $dir {
0 {incr x}
1 {incr y}
2 {incr x -1}
3 {incr y -1}
}
expr {$x < 0 || $x >= [image width $workarea] || $y < 0 || $y >= [image height $workarea]}
}
 
image create photo antgrid -width 100 -height 100
pack [label .l -image antgrid]
antgrid put white -to 0 0 99 99
set x [set y 50]
set dir 0
 
while 1 {
update
if {[step antgrid]} break
}
 
# Produce output in file
antgrid write ant.gif -format gif

[edit] TI-83 BASIC

The variable N counts the generation number.

PROGRAM:LANT
:ClrDraw
:0→N
:47→A
:31→B
:90→Θ
:Repeat getKey
:If pxl-Test(B,A)
:Then
:Θ+90→Θ
:Else
:Θ-90→Θ
:End
:Pxl-Change(B,A)
:A+cos(Θ°)→A
:B+sin(Θ°)→B
:N+1→N
:End
 

[edit] Whitespace

   	  			   	  		






















 



































 


 











 






 
 
 
 
 





Following is the pseudo-Assembly from which the above was generated.

; For easier access, the direction vector is stored at the end of the heap.
push 10003 dup push 100 store
push 1 sub dup push -1 store
push 1 sub dup push -100 store
push 1 sub dup push 1 store
 
0: ; Initialize the grid.
push 1 sub dup push 0 store
dup push 0 swap sub jn 0
push 5050 ; Start the ant at the center.
 
1: ; Make sure the ant's in bounds.
dup push 100 mod jn 2
dup push 100 div jn 2
push 100 copy 1 copy 1 mod sub jz 2
push 100 copy 1 copy 1 div sub jz 2
 
swap copy 1 load ; Get current cell state.
push 1 add push 2 mod ; Invert it.
copy 2 copy 1 store ; Then store it back.
push 2 mul push 5 add add push 4 mod ; Determine new direction.
swap copy 1 push 10000 add load add ; Update position accordingly.
jump 1
 
2: ; Initialize a counter and flow into the printer.
pop dup sub
 
3: ; Iterate over the cells.
dup load push 32 add ochr ; Print ' ' for off, '!' for on.
push 1 add dup ; Increment the counter.
push 100 mod jz 5 ; Branch at the end of a row.
4:
dup push 10000 sub jn 3 ; Go again unless counter is 10000.
pop exit ; All done, exit clean.
 
5: ; Print a newline and jump back to the counter check.
push 10 ochr jump 4

[edit] XPL0

AntXPL0.gif
include c:\cxpl\codes;          \intrinsic 'code' declarations
int X, Y, Dir;
[SetVid($13); \set 320x200 graphic video mode
X:= 50; Y:= 50; Dir:= 0; \start in middle facing east
repeat if ReadPix(X,Y) then \(black and white are reversed)
[Dir:= Dir-1;\left\ Point(X,Y, 0\black\)]
else [Dir:= Dir+1;\right\ Point(X,Y,$F\white\)];
case Dir & 3 of
0: X:= X+1; \east
1: Y:= Y+1; \south
2: X:= X-1; \west
3: Y:= Y-1 \north
other [];
until X<0 ! X>=100 ! Y<0 ! Y>=100;
X:= ChIn(1); \wait for keystroke
SetVid(3); \restore normal text mode
]
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