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