elixir-thinkinglisted

# Elixir Thinking Mental shifts required before writing Elixir. These contradict conventional OOP patterns. ## The Iron Law ``` NO PROCESS WITHOUT A RUNTIME REASON ``` Before creating a GenServer, Agent, or any process, answer YES to at least one: 1. Do I need mutable state persisting across calls? 2. Do I need concurrent execution? 3. Do I need fault isolation? **All three are NO?** Use plain functions. Modules organize code; processes manage runtime. ## The Three Decoupled Dimensions OOP couples behavior, state, and mutability together. Elixir decouples them: | OOP Dimension | Elixir Equivalent | |---------------|-------------------| | Behavior | Modules (functions) | | State | Data (structs, maps) | | Mutability | Processes (GenServer) | Pick only what you need. "I only need data and functions" = no process needed. ## "Let It Crash" = "Let It Heal" The misconception: Write careless code. The truth: Supervisors START processes. - Handle expected errors explicitly (`{:ok, _}` / `{:error, _}`) - Let unexpected errors crash → supervisor restarts ## Control Flow **Pattern matching first:** - Match on function heads instead of `if/else` or `case` in bodies - `%{}` matches ANY map—use `map_size(map) == 0` guard for empty maps - Avoid nested `case`—refactor to single `case`, `with`, or separate functions **Error handling:** - Use `{:ok, result}` / `{:error, reason}` for operations that can fail - Avoid raising exceptions for control flow - Use `with` for chaining `{