@effect-ts/system/_src/Effect/foldM.ts

Effect-TS is a zero dependency set of libraries to write highly productive, purely functional TypeScript at scale.

// ets_tracing: off

import { failureOrCause } from "../Cause/core.js"
import * as E from "../Either/index.js"
import { foldCauseM_, halt } from "./core.js"
import type { Effect } from "./effect.js"

/**
 * Recovers from errors by accepting one effect to execute for the case of an
 * error, and one effect to execute for the case of success.
 *
 * This method has better performance than `either` since no intermediate
 * value is allocated and does not require subsequent calls to `flatMap` to
 * define the next effect.
 *
 * The error parameter of the returned `IO` may be chosen arbitrarily, since
 * it will depend on the `IO`s returned by the given continuations.
 */
export function foldM_<R, E, A, R2, E2, A2, R3, E3, A3>(
  value: Effect<R, E, A>,
  failure: (failure: E) => Effect<R2, E2, A2>,
  success: (a: A) => Effect<R3, E3, A3>,
  __trace?: string
): Effect<R & R2 & R3, E2 | E3, A2 | A3> {
  return foldCauseM_(
    value,
    (cause) => E.fold_(failureOrCause(cause), failure, halt),
    success,
    __trace
  )
}

/**
 * Recovers from errors by accepting one effect to execute for the case of an
 * error, and one effect to execute for the case of success.
 *
 * This method has better performance than `either` since no intermediate
 * value is allocated and does not require subsequent calls to `flatMap` to
 * define the next effect.
 *
 * The error parameter of the returned `IO` may be chosen arbitrarily, since
 * it will depend on the `IO`s returned by the given continuations.
 *
 * @ets_data_first foldM_
 */
export function foldM<E, A, R2, E2, A2, R3, E3, A3>(
  failure: (failure: E) => Effect<R2, E2, A2>,
  success: (a: A) => Effect<R3, E3, A3>,
  __trace?: string
) {
  return <R>(value: Effect<R, E, A>): Effect<R & R2 & R3, E2 | E3, A2 | A3> =>
    foldM_(value, failure, success, __trace)
}