100 REM Langton!'s ant
110 REM ** Simulation
120 DIM Board(0 TO 99, 0 TO 99)
130 LET W = UBOUND(Board, 1) + 1
140 LET H = UBOUND(Board, 2) + 1
150 REM Start in the middle, facing East
160 LET X = INT(W / 2)
170 LET Y = INT(H / 2)
180 LET Dir = 0
190 DO
200    IF Board(X, Y) <> 0 THEN
210       LET Dir = Dir - 1
220       LET Board(X, Y) = 0
230    ELSE
240       LET Dir = Dir + 1
250       LET Board(X, Y) = 1
260    END IF
270    SELECT CASE MOD(Dir, 4)
280    CASE 0
290       LET X = X + 1
300    CASE 1
310       LET Y = Y + 1
320    CASE 2
330       LET X = X - 1
340    CASE 3
350       LET Y = Y - 1
360    END SELECT
370 LOOP WHILE X >= 0 AND X < W AND Y >= 0 AND Y < H
380 REM ** Visualization
390 SET WINDOW 0, W, 0, H
400 SET AREA COLOR 0
410 SET POINT COLOR 1
420 FOR X = 0 TO W - 1
430    FOR Y = 0 TO H - 1
440       IF Board(X, Y) <> 0 THEN GRAPH POINTS: X, Y
450    NEXT Y
460 NEXT X
470 END