What fp-ts type should I use for a synchronous operation that might fail with an error?

Use `Either `. The `Either` type is designed for synchronous operations where you need to handle errors explicitly.

How do I wrap a nullable value in fp-ts?

Use `O.fromNullable` to wrap a nullable value into an `Option` type, which handles the case where a value might be missing.

What's the difference between `TaskEither` and `Either` in fp-ts?

`Either` is for synchronous operations that may fail, while `TaskEither` is for asynchronous operations that may fail. Use `TaskEither` when your operation involves async calls.

How do I handle both success and failure cases in fp-ts?

Use pattern matching: `O.match(onNone, onSome)` for `Option` types and `E.match(onLeft, onRight)` for `Either` types, where you provide handlers for each case.

What should I use for an async operation with no errors but where the value might be missing?

Use `TaskOption `, which combines async handling with the possibility that a value may not be present.

Skill

Guide fp-ts Type Choices and Patterns

Name: fp-ts Quick Reference
Availability: OnlineOnly
Author: Antigravity

A decision-guide cheat sheet for choosing between fp-ts's Option, Either, Task, and TaskEither types.

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Updated last month

Source checked Aug 11, 2026

Version 15.12.0

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Why it matters

Get expert guidance on selecting the correct fp-ts types like Option, Either, Task, and TaskEither for your TypeScript projects. This asset provides a quick reference for common imports and one-line patterns to streamline your functional programming workflow.

Outcomes

What it gets done

Choose between fp-ts Option, Either, Task, and TaskEither.

Understand common fp-ts imports and their uses.

Apply one-line patterns for common fp-ts operations.

Learn pattern matching for Option and Either types.

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Run in your project directory:

curl -fsSL https://spark.entire.vc/get/ag-fp-types-ref | bash

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Overview

fp-ts Quick Reference

A decision-guide cheat sheet for choosing between fp-ts's Option, Either, Task, and TaskEither types, with common imports and one-line usage patterns. Use it when choosing between fp-ts types or needing quick guidance on imports and common patterns for a TypeScript flow.

What it does

A compact decision guide for choosing the right fp-ts type: a flowchart asking whether the operation is async, whether it involves errors, and whether the value might be missing, routing to Either<Error, Value> for sync-with-errors, Option<Value> for sync-nullable, TaskEither<Error, Value> for async-with-errors, TaskOption<Value> for async-nullable, or plain Task<Value> for async-no-failure. It lists the common imports for each type (Option, Either, TaskEither, Task, plus pipe/flow from fp-ts/function and Array utilities) and a one-line-pattern table (wrap nullable, default value, transform if exists, chain optionals, wrap try/catch, wrap async, run a pipe), plus pattern-matching examples for both Option and Either.

import { pipe, flow } from 'fp-ts/function'

When to use - and when NOT to

Use it when choosing between Option, Either, Task, TaskEither, or related fp-ts types, or needing quick guidance on imports and common patterns for a TypeScript flow, rather than a full fp-ts tutorial.

Inputs and outputs

Input: a TypeScript value or operation needing the right fp-ts wrapper type. Output: the recommended type - Option, Either, Task, or TaskEither - its import statement, and a matching one-line pattern.

Integrations

Companion reference to the more detailed fp-either-ref and fp-option-ref cheat sheets for deeper usage of each individual type.

Who it's for

TypeScript developers using fp-ts who need fast guidance on which type fits a given situation rather than re-deriving the decision each time.

FAQ

Common questions

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