Elixir Essentials

Use this skill before writing ANY .ex or .exs file.

RULES — Follow these with no exceptions

1. Use pattern matching over if/else for control flow and data extraction
2. Use @impl true before every callback function (mount, handle_event, handle_info, etc.)
3. Produce {:ok, result} | {:error, reason} tuples for fallible operations
4. Use with for 2+ sequential fallible operations instead of nested case
5. Use the pipe operator for 2+ chained transformations
6. Never nest if/else statements — use case, cond, or multi-clause functions
7. Use ? suffix for predicate functions, ! suffix for dangerous functions
8. Never write defensive code for impossible states — let it crash
9. Use @doc and @moduledoc for all public APIs
10. Prefer immutability — never mutate data in place
11. Don't use String.to_atom/1 on user input (atom table exhaustion)
12. Prefer for comprehensions before chaining 3+ Enum operations