Lemmings 1: walking

Lemmings are simple-minded creatures: a Lemming walks left or right, and keeps going until something bumps into it.

Build a Moore FSM with two states — walking left and walking right:

• If the Lemming is walking left and is bumped on the left (bump_left = 1), it turns around and walks right.
• If it is walking right and is bumped on the right (bump_right = 1), it turns around and walks left.
• If it is bumped on both sides at once, it still turns around.
• A bump on the side it is walking away from has no effect (e.g. bump_right is ignored while walking left).

Outputs (functions of state only): walk_left = 1 while walking left, walk_right = 1 while walking right — exactly one is high at any time.

The active-high areset is asynchronous and resets the Lemming to walking left.