Elixir Expert

Purpose

Provides expertise in Elixir development, Phoenix Framework, and OTP patterns. Covers concurrent programming, real-time features with LiveView, and building fault-tolerant distributed systems on the BEAM VM.

When to Use

• Building Elixir applications
• Developing Phoenix web applications
• Implementing real-time features with LiveView
• Using OTP patterns (GenServer, Supervisor)
• Building distributed systems on BEAM
• Designing fault-tolerant architectures
• Working with Ecto for database access

Quick Start

Invoke this skill when:

• Building Elixir applications
• Developing Phoenix web applications
• Implementing real-time features with LiveView
• Using OTP patterns
• Designing fault-tolerant systems

Do NOT invoke when:

• Building Ruby on Rails apps (use rails-expert)
• Building Node.js backends (use javascript-pro)
• Building Python backends (use python-pro)
• Infrastructure automation (use terraform-engineer)

Decision Framework

Concurrency Pattern:
├── Stateful process → GenServer
├── Async work → Task
├── Background job → Oban or Task.Supervisor
├── Event streaming → GenStage / Broadway
├── Real-time UI → Phoenix LiveView
└── External service → Retry with exponential backoff

Supervision Strategy:
├── Process can crash independently → one_for_one
├── Processes depend on each other → one_for_all
├── Ordered restart needed → rest_for_one
└── Dynamic children → DynamicSupervisor

Core Workflows

1. Phoenix Application Setup

1. Generate Phoenix project
2. Configure database with Ecto
3. Define schemas and migrations
4. Create contexts for business logic
5. Build controllers or LiveViews
6. Add authentication
7. Deploy with releases

2. OTP Application Design

1. Identify stateful components
2. Design supervision tree
3. Implement GenServers for state
4. Add proper error handling
5. Implement graceful shutdown
6. Test supervision strategies

3. Real-Time with LiveView

1. Generate LiveView module
2. Define assigns and state
3. Implement handle_event callbacks
4. Use pubsub for broadcasts
5. Optimize with temporary_assigns
6. Add JS hooks if needed

Best Practices

• Let it crash - design for failure recovery
• Use supervision trees for fault tolerance
• Keep GenServer state minimal
• Use contexts to organize business logic
• Prefer immutable data transformations
• Test concurrent code with async: true

Anti-Patterns

Anti-Pattern	Problem	Correct Approach
Large GenServer state	Memory and serialization	External storage, ETS
Defensive coding	Hides bugs	Let it crash, supervise
Blocking GenServer	Process bottleneck	Async tasks for I/O
No supervision	Unrecoverable crashes	Proper supervision tree
Mutable mindset	Bugs and race conditions	Embrace immutability