100 REM Langton's ant
110 CLS:W=95:H=44
120 X=INT(W/2):Y=INT(H/2)
130 REM Start in the middle, facing East
140 D=0
150 IF POINT(X,Y)=0 THEN 170
160 D=D-1:RESET(X,Y):GOTO 180
170 D=D+1:SET(X,Y)
180 ON D-INT(D/4)*4+1 GOSUB 220,230,240,250
190 IF X>=0 AND X<W AND Y>=0 AND Y<H THEN 150
200 SCREEN 1,13
210 END
220 X=X+1:RETURN
230 Y=Y+1:RETURN
240 X=X-1:RETURN
250 Y=Y-1:RETURN