roganjoshua

Maintaining state in a deep map

Coming from an object-oriented background I am writing a scrabble clone in elixir/phoenix in order to learn elixir and functional programming.

So my instinct is to have a state map like so:

game_state = {
  players: [
    {
      name: "Bob",
      rack: ["A"],
      score: 3
    },
    {
      name: "Alice",
      rack: ["B"],
      score: 10
    }
  ],
  board: [
    %Tile{
      letter: "A",
      row: 0,
      column: -1
    },
    %Tile{
      letter: "T",
      row: 0,
      column: 0 
    }
  ],
  bag: [
    "A",
    "A",
    " "
  ]
}

This is enough to maintain the state of the game.

Doing it this way seems to give flexiblity, storage and atomicity.

Writing interactions with this state feel a bit awkward and I am thinking I am stuck in OO world and I am building an object rather being functional.

I am thinking modules for bag, players and board.

new_game_state = game_state |> Players.add_player("Fred")
Am I going the wrong way with this?

I am doing things like if Enum.member?(player_state, &(&1.name == name)) do which is hauntingly familiar.

Martin

11 comments

#learning-elixir #object-oriented #state

0 651 11

2026-01-25 09:37:47 UTC

First Post!

mindok

Hi @roganjoshua,

There’s a pretty nice discussion about modelling a game (in this case Blackjack) from a functional and process point of view here: The Erlangelist - To spawn, or not to spawn?

Post #1

Most Liked

Asd

I’d suggest using Pathex for this.

put_in and other *_in functions have one big problem: they don’t work with arbitrary structures, because they expect every structure to implement Access behavior. Most of structures don’t implement it. And even if they do, it introduces unnecessary boilerplate and runtime overhead.

Pathex doesn’t have any of these problems, plus it is declarative, performant, extensible, can to nested sets (like mkdir -p crates intermediary folders, pathex creates intermediary structures), works with tuples, and even has smart things like lenses, filters, etc.

I am using Pathex to maintain complex state in GenServers where there is a lot of logic involved and I also use Pathex to traverse deeply nested structures like parsed HTML, verbose services responses (like ElasticSearch), etc.

Post #8

cmo

You could make the players state a map where their name or ID is the key. The board could be a map with {row, column} keys. That might make lookups a bit nicer.

Post #2

derek-zhou

You don’t have to colocate the functions that manipulate the struct in the same module that defines the struct. I frequently have one module with several sub-modules, all defined in the same file. The sub-modules have nothing but a struct, and all the business logic reside in the main module.

As for updating a struct couple levels deep, if you don’t like put_in/3 and update_in/3, there are fancier libraries that help with ergonomics. One was recently discussed in this forum: