Kara walks the slalom in an endless loop around the trees. He alternates left and right turns as follows:

while true
  while kara.treeLeft and not kara.treeRight
    quarterTurnLeft(kara)
  end

  quarterTurnRight(kara)

  while not kara.treeLeft and kara.treeRight
    quarterTurnRight(kara)
  end

  quarterTurnLeft(kara)
end