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 quarterTurn(kara) { kara.turnLeft } end quarterTurn(kara) { kara.turnRight } while not kara.treeLeft and kara.treeRight quarterTurn(kara) { kara.turnRight } end quarterTurn(kara) { kara.turnLeft } end