# One-Day Reversal Pattern
# Defined by Jesse Livermore

def LongReversal = Low < Low[1] and Close > Close[1] and Volume > Volume[1];
def ShortReversal = High > High[1] and Close < Close[1] and Volume > Volume[1];

plot UpArrow = if LongReversal then low - .0 else Double.NaN;
UpArrow.SetDefaultColor(Color.GREEN);
UpArrow.SetPaintingStrategy(PaintingStrategy.ARROW_UP);

plot DnArrow = if ShortReversal then high + .0 else Double.NaN;
DnArrow.SetDefaultColor(Color.RED);
DnArrow.SetPaintingStrategy(PaintingStrategy.ARROW_DOWN);

# end

Am not familiar with Think or Swim code but this code implements Jesse Livermore's One Day Reversal Pattern.