Module `grid`
* `Vector`
* `Grid`
* `directions`
* `directionNames`

Module `world`
* (`randomElement`)
* (`elementFromChar`)
* (`charFromElement`)
* `View`
* `World`
* `LifelikeWorld`

Module `simple_system`
* (`dirPlus`)
* `Wall`
* `WallFollower`
* `BouncingCritter`

Module `complex_system`
* `Wall` [duplicate]
* `Plant`
* `PlantEater`
* `SmartPlantEater`
* `Tiger`

Add Chapter 10, exercise 02
Add Chapter 10, exercise 02
