Kara walks from left to right and from right to left, alternatively, and "inverts" the current row of the image. The main program is the following:
walkingLeft2Right = true while not (kara.treeFront and (kara.treeLeft or kara.treeRight)) if walkingLeft2Right left2right(kara) else right2left(kara) end walkingLeft2Right = !walkingLeft2Right end