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Documentation / AGENT SKILL
fp-option-ref
0
Provide an Option type reference for nullable values and optional data.
Quick reference for Option type. Use when user needs to handle nullable values, optional data, or wants to avoid null checks.
Understand the trade-offs.
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Original instructions from the publisher’s SKILL.md
# Option Quick Reference
Option = value that might not exist. `Some(value)` or `None`.
## When to Use
- You need a quick fp-ts reference for nullable or optional values.
- The task involves eliminating null checks, safe property access, or optional chaining with `Option`.
- You want a short reference card rather than a full migration guide.
## Create
```typescript
import * as O from 'fp-ts/Option'
O.some(5) // Some(5)
O.none // None
O.fromNullable(x) // null/undefined → None, else Some(x)
O.fromPredicate(x > 0)(x) // false → None, true → Some(x)
```
## Transform
```typescript
O.map(fn) // Transform inner value
O.flatMap(fn) // Chain Options (fn returns Option)
O.filter(predicate) // None if predicate false
```
## Extract
```typescript
O.getOrElse(() => default) // Get value or default
O.toNullable(opt) // Back to T | null
O.toUndefined(opt) // Back to T | undefined
O.match(onNone, onSome) // Pattern match
```
## Common Patterns
```typescript
import { pipe } from 'fp-ts/function'
import * as O from 'fp-ts/Option'
// Safe property access
pipe(
O.fromNullable(user),
O.map(u => u.profile),
O.flatMap(p => O.fromNullable(p.avatar)),
O.getOrElse(() => '/default-avatar.png')
)
// Array first element
import * as A from 'fp-ts/Array'
pipe(
users,
A.head, // Option<User>
O.map(u => u.name),
O.getOrElse(() => 'No users')
)
```
## vs Nullable
```typescript
// ❌ Nullable - easy to forget checks
const name = user?.profile?.name ?? 'Guest'
// ✅ Option - explicit, composable
pipe(
O.fromNullable(user),
O.flatMap(u => O.fromNullable(u.profile)),
O.map(p => p.name),
O.getOrElse(() => 'Guest')
)
```
Use Option when you need to **chain** operations on optional values.