# Repository Instructions

This is a **0.x library** — expect breaking changes. Backward compatibility is not a priority. When refactoring:
- Delete old code rather than deprecate
- Simplify aggressively
- Don't add compatibility shims

## Commit Messages

Use a concise Conventional Commit subject, e.g.
`feat(mcp): add stateful sessions`.

For non-trivial commits, add a short body covering what changed and how
it was verified.

## PTC-Lisp Changes

Clojure compatibility is the default, but sandbox safety and recoverable
signal values take precedence for Clojure-named functions where Clojure
would raise; Java-named dot methods keep Java semantics.

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<!-- usage-rules-header -->
# Usage Rules

**IMPORTANT**: Consult these usage rules early and often when working with the packages listed below.
Before attempting to use any of these packages or to discover if you should use them, review their
usage rules to understand the correct patterns, conventions, and best practices.
<!-- usage-rules-header-end -->

<!-- usage_rules-start -->
## usage_rules usage
_A dev tool for Elixir projects to gather LLM usage rules from dependencies_

## Using Usage Rules

Many packages have usage rules, which you should *thoroughly* consult before taking any
action. These usage rules contain guidelines and rules *directly from the package authors*.
They are your best source of knowledge for making decisions.

Run `mix usage_rules.*` tasks from the repo root by default. Some nested Mix projects, such as
`mcp_server/`, may not define these tasks; if a task is unavailable there, retry from the repo root.

Use `mix usage_rules.search_docs` first when the exact dependency module or
function is uncertain. Only call `mix usage_rules.docs` with a confirmed module
or `Module.function/arity` returned by search/docs; `usage_rules.docs` does not not accept package filters such as `-p`.

## Modules & functions in the current app and dependencies

When looking for docs for modules & functions that are dependencies of the current project,
or for Elixir itself, use `mix usage_rules.docs`

```
# Search a whole module
mix usage_rules.docs Enum

# Search a specific function
mix usage_rules.docs Enum.zip

# Search a specific function & arity
mix usage_rules.docs Enum.zip/1
```


## Searching Documentation

You should also consult the documentation of any tools you are using, early and often. The best 
way to accomplish this is to use the `usage_rules.search_docs` mix task. Once you have
found what you are looking for, use the links in the search results to get more detail. For example:

```
# Search docs for all packages in the current application, including Elixir
mix usage_rules.search_docs Enum.zip

# Search docs for specific packages
mix usage_rules.search_docs Req.get -p req

# Search docs for multi-word queries
mix usage_rules.search_docs "making requests" -p req

# Search only in titles (useful for finding specific functions/modules)
mix usage_rules.search_docs "Enum.zip" --query-by title
```


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<!-- usage_rules:elixir-start -->
## usage_rules:elixir usage
# Elixir Core Usage Rules

## Pattern Matching
- Use pattern matching over conditional logic when possible
- Prefer to match on function heads instead of using `if`/`else` or `case` in function bodies
- `%{}` matches ANY map, not just empty maps. Use `map_size(map) == 0` guard to check for truly empty maps

## Error Handling
- Use `{:ok, result}` and `{:error, reason}` tuples for operations that can fail
- Avoid raising exceptions for control flow
- Use `with` for chaining operations that return `{:ok, _}` or `{:error, _}`

## Common Mistakes to Avoid
- Elixir has no `return` statement, nor early returns. The last expression in a block is always returned.
- Don't use `Enum` functions on large collections when `Stream` is more appropriate
- Avoid nested `case` statements - refactor to a single `case`, `with` or separate functions
- Don't use `String.to_atom/1` on user input (memory leak risk)
- Lists and enumerables cannot be indexed with brackets. Use pattern matching or `Enum` functions
- Prefer `Enum` functions like `Enum.reduce` over recursion
- When recursion is necessary, prefer to use pattern matching in function heads for base case detection
- Using the process dictionary is typically a sign of unidiomatic code
- Only use macros if explicitly requested
- There are many useful standard library functions, prefer to use them where possible

## Function Design
- Use guard clauses: `when is_binary(name) and byte_size(name) > 0`
- Prefer multiple function clauses over complex conditional logic
- Name functions descriptively: `calculate_total_price/2` not `calc/2`
- Predicate function names should not start with `is` and should end in a question mark.
- Names like `is_thing` should be reserved for guards

## Data Structures
- Use structs over maps when the shape is known: `defstruct [:name, :age]`
- Prefer keyword lists for options: `[timeout: 5000, retries: 3]`
- Use maps for dynamic key-value data
- Prefer to prepend to lists `[new | list]` not `list ++ [new]`

## Mix Tasks

- Use `mix help` to list available mix tasks
- Use `mix help task_name` to get docs for an individual task
- Read the docs and options fully before using tasks

## Testing
- Run tests in a specific file with `mix test test/my_test.exs` and a specific test with the line number `mix test path/to/test.exs:123`
- Limit the number of failed tests with `mix test --max-failures n`
- Use `@tag` to tag specific tests, and `mix test --only tag` to run only those tests
- Use `assert_raise` for testing expected exceptions: `assert_raise ArgumentError, fn -> invalid_function() end`
- Use `mix help test` to for full documentation on running tests

## Debugging

- Use `dbg/1` to print values while debugging. This will display the formatted value and other relevant information in the console.

<!-- usage_rules:elixir-end -->
<!-- usage_rules:otp-start -->
## usage_rules:otp usage
# OTP Usage Rules

## GenServer Best Practices
- Keep state simple and serializable
- Handle all expected messages explicitly
- Use `handle_continue/2` for post-init work
- Implement proper cleanup in `terminate/2` when necessary

## Process Communication
- Use `GenServer.call/3` for synchronous requests expecting replies
- Use `GenServer.cast/2` for fire-and-forget messages.
- When in doubt, use `call` over `cast`, to ensure back-pressure
- Set appropriate timeouts for `call/3` operations

## Fault Tolerance
- Set up processes such that they can handle crashing and being restarted by supervisors
- Use `:max_restarts` and `:max_seconds` to prevent restart loops

## Task and Async
- Use `Task.Supervisor` for better fault tolerance
- Handle task failures with `Task.yield/2` or `Task.shutdown/2`
- Set appropriate task timeouts
- Use `Task.async_stream/3` for concurrent enumeration with back-pressure

<!-- usage_rules:otp-end -->
<!-- usage-rules-end -->
