fp-pack skill

---
name: fp-pack
description: Use when working in projects that use fp-pack; follow pipe, SideEffect, and curry guidelines.
metadata:
  short-description: fp-pack workflow
  version: {{version}}
---

# fp-pack AI Agent Skills

Document Version: {{version}}

Additional materials (optional):
- constraints/ (rules, mistakes, troubleshooting)
- reference/ (composition, currying, TypeScript inference)
- examples/ (quick examples)

## ⚠️ Activation Condition (Read First)

These guidelines apply **only when `fp-pack` is installed** in the current project.

Before following this document:
- Check `package.json` for `fp-pack` in dependencies/devDependencies
- Check `node_modules/fp-pack` exists
- Check existing code imports from `fp-pack` or `fp-pack/stream`

If `fp-pack` is **not** installed, use the project's existing conventions. Do **not** suggest adding fp-pack unless the user asks.

---

## Core Rules (Keep In Memory)

- Use `pipe`/`pipeAsync` for 2+ steps; for a single step, call the function directly.
- Every pipe checks each step; do not use the deprecated `*Strict` variants (`pipeStrict`, `pipeAsyncStrict`, `pipeSideEffectStrict`, `pipeAsyncSideEffectStrict`).
- Prefer value-first: `pipe(value, ...)` / `pipeAsync(value, ...)` runs immediately and improves inference (the input anchors types). Use functions-first only when you need a reusable pipeline.
- Let pipe infer intermediate parameters; do not add assertions to silence a broken chain. Contextual inference covers 32 steps after the first argument. Compose smaller pipelines beyond that limit; longer already typed chains remain checked.
- `pipeWithDeps` infers intermediate values and intersects dependency contracts. Default and deprecated variants have identical checks. Annotate the dependency contract where needed, not every value parameter.
- If the first arg is a function, it's treated as composition; wrap function values with `from()`.
- Keep pipeline functions **unary**; prefer data-last, curried helpers.
- `map`/`filter` are for arrays/iterables, not single values.
- Use `from()` only for constants or 0-arg pipelines (including function values you need to pass as data). Otherwise pass data as the first argument.
- Use `pipeSideEffect*` only when you need early exit; otherwise use `pipe`/`pipeAsync`.
- Never call `runPipeResult`/`matchSideEffect` inside pipelines; call at boundaries.
- Prefer `isSideEffect` for precise narrowing; `runPipeResult` for unwrapping (pipe results are precise; use generics only for values you widened yourself).
- `SideEffect` is an instance type: use `SideEffect<E>` (not `typeof SideEffect`).