AgentSkillsCN

functional-programming

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SKILL.md
--- frontmatter
name: functional-programming
description: Comprehensive functional programming guide covering core principles and patterns across multiple languages (Python, Rust, TypeScript, Lua, C). Use when OpenCode or Claude needs to write any code.

Functional Programming Skill

This skill guides you in applying Functional Programming (FP) principles to any language, even imperative ones.

For full multi-language code examples (Python, Rust, TypeScript, Lua, C), see references/guide.md.

Core Guidelines

0. No Global State

Rule: Never use global variables or mutable shared state. Pass dependencies explicitly through parameters or dependency injection. Pattern: Use Actors or Dependency Injection to manage state.

1. Pure Functions Only

Rule: All functions must depend only on their input arguments. They must never mutate shared state or perform I/O. Why: Ensures determinism and testability.

2. Isolate Side Effects

Rule: I/O, randomness, database access, and system calls must be in a separate "shell" layer, never mixed with business logic. Pattern: "Functional Core, Imperative Shell".

3. Functional Core, Imperative Shell

Rule: Write all business logic as pure functions. Only the outer layers (main, controllers, handlers) perform effects and orchestrate data flow.

4. Monadic Error Handling

Rule: Use Result or Option types to handle failures and optional values. Don't: Do not use exceptions for control flow. Exceptions should only be for unrecoverable crashes.

5. Composable Concurrency

Rule: Use async/await, Task, or Future wrappers. Don't: Avoid raw threading or locking mutexes manually if possible. Use message passing.

6. Actor Model

Rule: Encapsulate mutable state within Actors that communicate via message passing. Pattern: Actors process messages one at a time, ensuring no concurrent mutation of internal state.

7. Request-Reply Actor Pattern

Rule: For request-response interactions, embed a "reply channel" in the request message. Benefit: Enforces type safety and correlation between requests and responses.

Quick Reference

Do:

  • •Write pure, deterministic functions.
  • •Model effects explicitly (Result, Option).
  • •Keep side effects at the boundaries of your application.
  • •Encapsulate concurrency with actors.

Don't:

  • •Share mutable state between components.
  • •Mix I/O with computation in the same function.
  • •Use isinstance checks (use pattern matching instead).
  • •Use exceptions for expected errors.

Implementation Details

The referenced guide references/guide.md contains detailed implementations for:

  • •Dependency Injection (Python, Rust, TS)
  • •Pure Functions (Python, C, Rust, Lua)
  • •Effect Isolation (Python, C, Rust, Lua)
  • •Functional Core/Imperative Shell (Python, C, Rust, Lua)
  • •Monadic Error Handling (Python, C, Rust, Lua)
  • •Actor Model (Python, TS, Rust, Lua)
  • •Request-Reply Pattern (Python, TS, Rust, Lua)

When implementing these patterns, check the reference guide to ensure you are using the idiomatic approach for the target language.