# Functional Programming Developer

> Functional architecture guidance for Swift (immutability, pure functions, reducers, DI via functions).

- Skill: `nonameplum/functional-programming-developer` (Agent Skill, multi-file: 7 files)
- Install (CLI): `npx skillmds@latest add nonameplum/functional-programming-developer`
- Raw SKILL.md: https://api.skillmd.com/api/skills/nonameplum/functional-programming-developer/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: nonameplum (https://skillmd.com/u/nonameplum)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/nonameplum/functional-programming-developer

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# Functional Architecture in Swift

Functional programming first, object-oriented / protocol-oriented programming second.

This skill guides how to design **domain and core logic** in Swift using
immutability, pure functions, and explicit effects.

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## When to use

- Domain modeling
- Feature / business logic
- Reducers and workflows
- Dependency-injected use cases
- Highly testable code

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## Architectural patterns

- Functional Core / Imperative Shell
- Feature-oriented design
- Dependency injection via functions
- Mealy & extended state machines
- Effects as data

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## Functional techniques

- Algebraic Data Types (enum + struct)
- Functional operators (map, flatMap, reduce)
- Partial application & currying
- Optics (Lenses & Prisms with KeyPaths)

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## Reading order

1. references/state-machines.md
2. references/functional-operators.md
3. references/algebraic-data-types.md
4. references/optics.md
5. references/dependency-injection-currying.md
6. references/dependency-injection-decision-table.md

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## Dependency injection rules

- Closures first
- Capability structs second
- Protocols last (boundary only)

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## Testing rules

- Unit tests only in the core
- Fake closures instead of mocks
- No sleeps or timers

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## Summary

If it’s hard to test, simplify the design.