# Functional Programming > Use when writing functional code - covers FP best practices (Lea differs from traditional FP languages) - Skill: `tomevault-io/functional-programming` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/functional-programming` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/functional-programming/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/functional-programming --- # Functional Programming Best Practices ## Quick Start ``` -- Prefer pure functions and immutable data let double = (x) -> x * 2 [1, 2, 3] /> map(double) /> filter((x) -> x > 2) ``` ## Core Principles - **Immutability**: Use `let` by default, `maybe` only when mutation is necessary - **Pure functions**: No side effects, same input always produces same output - **Composition**: Build complex behavior from simple, composable functions - **Higher-order functions**: Pass functions as arguments, return functions ## Lea-Specific Warnings **Lea differs from traditional FP languages:** - **No currying** - Use placeholders: `5 /> add(3, input)` - **Pipes prepend** - `x /> fn(a)` becomes `fn(x, a)` - **Mutable bindings** - `maybe` allows mutation; avoid unless necessary - **No monads** - Async uses `#async` decorator instead - **Opt-in types** - Add `:: Type :> ReturnType`, use `#strict` for enforcement ## Notes - Prefer `let` over `maybe` - Use pipelines (`/>`) for left-to-right data flow - Callbacks receive `(element, index)` --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/mcclowes) — claim your Tome and manage your conversions.