Task
Produce a graphical or ASCII-art representation of a  Sierpinski arrowhead curve  of at least order  3.




var rules = Hash(
    x => 'yF+xF+y',
    y => 'xF-yF-x',
)
 
var lsys = LSystem(
    width:  550,
    height: 500,
 
    xoff: -20,
    yoff: -30,
 
    len:   4,
    turn: -90,
    angle: 60,
    color: 'dark green',
)
 
lsys.execute('xF', 7, "sierpiński_arrowhead.png", rules)