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

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((n: number) => n > 0)(x) // false → None, true → Some(x)

Transform

O.map(fn)              // Transform inner value
O.flatMap(fn)          // Chain Options (fn returns Option)
O.filter(predicate)    // None if predicate false

Extract

O.getOrElse(() => fallbackValue)  // 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

import { pipe } from 'fp-ts/function'
import * as O from 'fp-ts/Option'

// Safe property access
pipe(
  O.fromNullable(user),
  O.flatMap(u => O.fromNullable(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

// Nullable: concise and safe for a short access chain
const name = user?.profile?.name ?? 'Guest'

// Option: explicit and composable across multiple operations
pipe(
  O.fromNullable(user),
  O.flatMap(u => O.fromNullable(u.profile)),
  O.flatMap(p => O.fromNullable(p.name)),
  O.getOrElse(() => 'Guest')
)

Use Option when you need to chain operations on optional values.

Limitations

• Use this skill only when the task clearly matches the scope described above.
• Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
• Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.

Reference scope

These are fp-ts 2.x fragments. Supply application variables, types, validators and imports, and check the installed version. map does not catch thrown exceptions. Task has no typed error channel; an improperly wrapped promise can still reject. Use tryCatch at fallible boundaries.

Official API: fp-ts modules.