step :: Probe -> Probe
step probe = probe & pos .~ (probe ^. pos ^+^ probe ^. vel) & vel .~ vel'
where vel' = V2 (max 0 (vx - 1)) (vy - 1)
step :: Probe -> Probe
step probe = probe & pos .~ (probe ^. pos ^+^ probe ^. vel) & vel .~ vel'
where vel' = V2 (max 0 (vx - 1)) (vy - 1)