ReaderT

How-to

Problem

I am searching for some type like ReaderIOEither I cannot find it in fp-ts, what can I do?

Solution

You can build what you need by using IOEither + ReaderT.

Here's a sketch

import * as IOE from 'fp-ts/IOEither'
import * as ReaderT from 'fp-ts/ReaderT'

export interface ReaderIOEither<R, E, A> {
  (r: R): IOE.IOEither<E, A>
}

declare module 'fp-ts/HKT' {
  interface URItoKind3<R, E, A> {
    readonly ReaderIOEither: ReaderIOEither<R, E, A>
  }
}

export const map = /*#__PURE__*/ ReaderT.map(IOE.Functor)
export const ap = /*#__PURE__*/ ReaderT.ap(IOE.ApplyPar)
export const chain = /*#__PURE__*/ ReaderT.chain(IOE.Chain)
// etc...