fp-taskeither-ref

name	fp-taskeither-ref
description	Quick reference for TaskEither. Use when user needs async error handling, API calls, or Promise-based operations that can fail.
type	skill
created	2026-02-27T00:00:00.000Z
domain	communication-content
category	documentation
risk	unknown
source	community
tags	["skill","communication-content","documentation","taskeither","ref"]

TaskEither Quick Reference

TaskEither = async operation that can fail. Like Promise<Either<E, A>>.

When to Use

• You need a quick fp-ts reference for async operations that can fail.
• The task involves API calls, Promise wrapping, or composing asynchronous error-handling pipelines.
• You want a concise cheat sheet for TaskEither operators and patterns.

Create

import * as TE from 'fp-ts/TaskEither'

TE.right(value)          // Async success
TE.left(error)           // Async failure
TE.tryCatch(asyncFn, toError)  // Promise → TaskEither
TE.fromEither(either)    // Either → TaskEither

Transform

TE.map(fn)               // Transform success value
TE.mapLeft(fn)           // Transform error
TE.flatMap(fn)           // Chain (fn returns TaskEither)
TE.orElse(fn)            // Recover from error

Execute

// TaskEither is lazy - must call () to run
const result = await myTaskEither()  // Either<E, A>

// Or pattern match
 (
  myTaskEither,
  .(
     .(err),
     .(val)
  )
)()