# Haskell > Guides for Haskell code. Use when writing Haskell code. Use when this capability is needed. - Skill: `tomevault-io/haskell` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/haskell` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/haskell/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/haskell --- - Avoid defining functions by cases on their last argument, use `LambdaCase` - Avoid list indexing (`!!`) - Avoid partial functions (`head`, `undefined`) except in tests - Instead of nesting `Either`, `Maybe`, and tuples, make a new `data` type - `LambdaCase` now supports `\cases` for multiple arguments - Never return tuples of arity higher than 2, just make a new `data` type - Never use `unsafeCoerce` or `unsafePerformIO` - Only use `Either` for error handling, otherwise make a new `data` type - Use `Data.Text.IO` for I/O --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/langston-barrett) — claim your Tome and manage your conversions.