Book-Functional-Web-Dev-W-Elixir
https://pragprog.com/book/lhelph/functional-web-development-with-elixir-otp-and-phoenix
Original Source Code from Author
To setup Continuous testing with mix_test_watch
0 Mapping Our Route
Lay The Foundation With Elixir
Domain in native Elixir instead of ORM
Maintain state with Agents
Interface to wrap agents in GenServer
Finite state machine to manage transition
Supervision tree for fault tolerance
Add a Web Interface With Phoenix
UI in Phoenix (without Ecto)
Functional Web Development
Functional => composition at every layer scaled to application. :w
The Game of Islands
Similar to Battleship
-
10x10 grid: A-J, 1-10
-
player sets islands
-
other player "forests" island by guessing location
-
winner forests all opponents islands
C = Coordinate I = Island %{} = Map %A{} = Struct [] = List Game --> State Machine / \ / \ P1 P2 Player --> Board %{C,C,C,..} --> Island Set %IslandSet{I,I,I,I,I} I --> [C...][C...]...
1 Define the Functional Core in Elixir
The Benefits
(Web) frameworks imply a certain domain and make business domain fuzzy
DB also distorts the domain
Let’s Build It
$ mix new islands_engine --sup
mix new create skeleton
$ tree
.
├── README.md
├── config
│ └── config.exs
├── lib
│ ├── islands_engine
│ │ └── application.ex
│ └── islands_engine.ex
├── mix.exs
└── test
├── islands_engine_test.exs
└── test_helper.exs
Discover the Entities, Model the Domain
- Players need to be able to position islands on their own boards.
- Players need to be able to guess coordinates on their opponent’s boards.
- The game needs to determine if a guess results in a hit or a miss.
- The game needs to determine if a guess results in a forested island.
- The game needs to determine if a guess results in a win.
Coordinates
3 data struct options:
- tuple
{1, 1}but cannot be encoded as JSON - map
%{row: 1, col: 1} - structs are like maps but they offer compile time checks on keys and runtime checks on type
- alias Coordinate
- defstruct :row, :col with @enforce_keys to ensure both attributes are present
- Coordinate.new with row/col validation they are within 1..10
$ iex -S mix to play with Coordinate
iex(2)> alias IslandsEngine.Coordinate
IslandsEngine.Coordinate
iex(3)> Coordinate.new(1, 1)
{:ok, %IslandsEngine.Coordinate{col: 1, row: 1}}
iex(4)> Coordinate.new(-1, 1)
{:error, :invalid_coordinate}
iex(5)> %Coordinate{row: 5}
** (ArgumentError) the following keys must also be given when building struct IslandsEngine.Coordinate: [:col]
(islands_engine) expanding struct: IslandsEngine.Coordinate.__struct__/1
iex:5: (file)Guesses
Guess == :hits + :misses
Use MapSet to ensure uniqueness
Islands
Islands
- come in five different shapes,
:atoll,:dot,:l_shape,:s_shape, and:square. - made up of group of coordinates
- determine if island is forested
List comparison:
[1,2] == [2,1]is falseMapSet.equal?(MapSet.new([1, 2]), MapSet.new([2, 1]))is true
Islands can be thought of as an origin coordinate with offsets.
e.g. :square = Origin{row,col} + Offset{1,0} + Offset{0,1} + Offset{1,1}
We can use Enum.reduce/2 to iterate over the offsets in building the island
💥 We have to check that the offsets are valid, better is Enum.reduce_while/3
IslandsEngine.Island create Islands with defined shapes
Boards
IslandsEngine.Board is simple. For now just return empty map
- will hold player islands
- broker messages
- check forests
- etc
Transforming Data
Guesses
- track guesses. don't need to remove them, only write
- add guessed coord to Guesses map
- ^ calculate if hit or miss
IslandsEngine.Guesses add :hit or :miss
Island
3 roles:
- positioning islands
- guessing coordinates
- checking for a forested island.
Need to check for overlaps when placing islands. We can use MapSet.disjoint/2
Next we use MapSet.member?/2 to check if a coordinate is a member of a set
Island.guess(island, coordinate)
Check if Island.forested?(island)
Add a function to return list of valid island types
Check that we can get Island.types
Board
Board roles:
- knows about and addresses all islands
- delegate function calls to islands
Board.overlaps_existing_island?
Use Enum.find_value/3 to
find a hit island based on coordinate. Otherwise return :miss
Board.check_all_islands(board, coordinate)
Board.guess_response({key, island}, board)
Board.guess(board, %Coordinate{} = coordinate)
Board.position_island(board, key %Island{} = island)
Board should now be usable
Putting the Pieces Together
IslandsEngineTest add an assert