machinery
A lightweight Elixir state machine library with Phoenix integration, providing a simple DSL for managing state transitions.
What is machinery?
Machinery is a lightweight state machine library for Elixir that provides a simple DSL for declaring states and transitions. It simplifies state management in applications by offering a clean, unobtrusive layer for modeling workflows and business logic, with built-in support for Phoenix projects.
Elixir developers, particularly those building Phoenix applications, who need to manage state transitions in models like user accounts, orders, or document workflows.
Developers choose Machinery for its minimalistic design that integrates seamlessly with Elixir's functional paradigms, offering essential features like guard functions, callbacks, and persistence without imposing a heavy framework.
Overview
Elixir State machine thin layer for structs
Use Cases
Best For
- Modeling business logic workflows in Elixir applications, such as order processing or user onboarding steps.
- Adding state management to Phoenix schemas with automatic database persistence via a custom persist function.
- Implementing audit trails by logging every state transition for debugging and compliance purposes.
- Enforcing conditional transitions with guard functions that prevent invalid state changes based on business rules.
- Handling side effects around transitions using before and after callbacks for actions like sending notifications.
- Creating flexible state machines with wildcard transitions that apply from any state to a specific one.
Not Ideal For
- Applications requiring complex state hierarchies like nested or parallel states, as Machinery only supports flat transitions.
- Projects needing built-in graphical tools for designing or debugging state diagrams, since it's code-focused without visualization.
- Teams that prefer convention-over-configuration frameworks with automated state machine generation from models or schemas.
- Systems where state transitions must be distributed or handled asynchronously with built-in support, as Machinery is synchronous and requires manual async handling.
Pros & Cons
Pros
Declaring states and transitions uses a clean keyword-based DSL, as shown in the example where states and transitions are defined concisely in a module.
Seamlessly integrates with Phoenix and Ecto schemas, with specific instructions for adding state fields and using persist functions for database persistence.
Guard functions with pattern matching allow conditional transitions, preventing invalid changes based on business logic, demonstrated in the guard_transition example.
Supports before and after callbacks for side effects, enabling actions like notifications or data updates around transitions, with examples for each.
Cons
Users must implement their own persist function to save state changes to the database, adding boilerplate code and potential for errors if not handled correctly.
Lacks support for complex state machine patterns like hierarchical states, history states, or event sourcing, which might be necessary for sophisticated workflows.
The README does not specify how errors in callbacks are managed, risking silent failures if callbacks raise exceptions without proper error handling.
Frequently Asked Questions
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