# Fp Either Ref

> Quick reference for Either type. Use when user needs error handling, validation, or operations that can fail with typed errors.

- Skill: `techwavedev/fp-either-ref` (Agent Skill)
- Install (CLI): `npx skillmds@latest add techwavedev/fp-either-ref`
- Raw SKILL.md: https://api.skillmd.com/api/skills/techwavedev/fp-either-ref/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: techwavedev (https://skillmd.com/u/techwavedev)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/techwavedev/fp-either-ref

---


# Either Quick Reference

Either = success or failure. `Right(value)` or `Left(error)`.

## Create

```typescript
import * as E from 'fp-ts/Either'

E.right(value)           // Success
E.left(error)            // Failure
E.fromNullable(err)(x)   // null → Left(err), else Right(x)
E.tryCatch(fn, toError)  // try/catch → Either
```

## Transform

```typescript
E.map(fn)                // Transform Right value
E.mapLeft(fn)            // Transform Left error
E.flatMap(fn)            // Chain (fn returns Either)
E.filterOrElse(pred, toErr) // Right → Left if pred fails
```

## Extract

```typescript
E.getOrElse(err => default)  // Get Right or default
E.match(onLeft, onRight)     // Pattern match
E.toUnion(either)            // E | A (loses type info)
```

## Common Patterns

```typescript
import { pipe } from 'fp-ts/function'
import * as E from 'fp-ts/Either'

// Validation
const validateEmail = (s: string): E.Either<string, string> =>
  s.includes('@') ? E.right(s) : E.left('Invalid email')

// Chain validations (stops at first error)
pipe(
  E.right({ email: 'test@example.com', age: 25 }),
  E.flatMap(d => pipe(validateEmail(d.email), E.map(() => d))),
  E.flatMap(d => d.age >= 18 ? E.right(d) : E.left('Must be 18+'))
)

// Convert throwing code
const parseJson = (s: string) => E.tryCatch(
  () => JSON.parse(s),
  (e) => `Parse error: ${e}`
)
```

## vs try/catch

```typescript
// ❌ try/catch - errors not in types
try {
  const data = JSON.parse(input)
  process(data)
} catch (e) {
  handleError(e)
}

// ✅ Either - errors explicit in types
pipe(
  E.tryCatch(() => JSON.parse(input), String),
  E.map(process),
  E.match(handleError, identity)
)
```

Use Either when **error type matters** and you want to chain operations.

---

<!-- AGI-INTEGRATION-START -->

## AGI Framework Integration

> **Adapted for [@techwavedev/agi-agent-kit](https://www.npmjs.com/package/@techwavedev/agi-agent-kit)**
> Original source: [antigravity-awesome-skills](https://github.com/sickn33/antigravity-awesome-skills)

### Memory-First Protocol

Retrieve prior design decisions (color palettes, typography, spacing scales) to maintain visual consistency across sessions. Cache generated design tokens.

```bash
# Check for prior frontend/design context before starting
python3 execution/memory_manager.py auto --query "design system decisions and component patterns for Fp Either Ref"
```

### Storing Results

After completing work, store frontend/design decisions for future sessions:

```bash
python3 execution/memory_manager.py store \
  --content "Design system: adopted 8px grid, Inter font family, HSL color tokens with dark mode support" \
  --type decision --project <project> \
  --tags fp-either-ref frontend
```

### Multi-Agent Collaboration

Share design decisions with backend agents (API contract changes) and QA agents (visual regression baselines).

```bash
python3 execution/cross_agent_context.py store \
  --agent "<your-agent>" \
  --action "Implemented UI components — new design system with accessibility compliance (WCAG 2.1 AA)" \
  --project <project>
```

### Design Memory Persistence

Store design system tokens and component decisions in Qdrant so any agent on any platform (Claude, Gemini, Cursor) can retrieve and apply consistent styling.

<!-- AGI-INTEGRATION-END -->