Adapters: switchFn, liftMap, tee

Adapters — barrel export.

Re-exports adapter/interop functions for bridging between Result and other patterns.

Functions

fromOption()

Converts an Option to a Result, providing an error for the None case. Some(value) → Ok(value), None → Err(errorOnNone).

export function fromOption<E>(errorOnNone: E): <A>(opt: IOption<A>) => IResultOfT<A, E>;
export function fromOption<A, E>(errorOnNone: E, opt: IOption<A>): IResultOfT<A, E>;

Defined in: adapters/fromOption.ts

Example

import { fromOption } from '@sandlada/result/adapters';
import { ofSome, ofNone } from '@sandlada/result/option';
fromOption('missing', ofSome(42)); // Ok(42)
fromOption('missing', ofNone()); // Err('missing')

---

liftMap()

Converts a one-track function into a two-track function. Alias for map — a teaching aid for the Wlaschin three-shape model.

export function liftMap<A, B>(f: (a: A) => B): <E>(r: IResultOfT<A, E>) => IResultOfT<B, E>;
export function liftMap<A, B, E>(f: (a: A) => B, r: IResultOfT<A, E>): IResultOfT<B, E>;

Defined in: adapters/liftMap.ts

Example

import { liftMap } from '@sandlada/result/adapters';
import { pipe } from '@sandlada/result/composition';
import { ok } from '@sandlada/result/factories';
pipe(ok(21), liftMap(x => x * 2)); // Ok(42)

---

switchFn()

Converts a one-track (plain) function into a switch function — lifts it to return a Result.

Optional errorFn (when supplied) maps the caught exception to a typed error; without it the error type defaults to unknown — mirrors tryCatch/fromPromise.

Wlaschin equivalent: succeed ∘ f

export function switchFn<A, B, E = unknown>(
    f: (a: A) => B,
    errorFn?: (error: unknown) => E,
): (a: A) => IResultOfT<B, E>;

Defined in: adapters/switchFn.ts

Example

import { switchFn } from '@sandlada/result/adapters';
const safe = switchFn((x: number) => x * 2);
safe(21); // Ok(42)

---

switchFnAsync()

Converts a one-track async function into an async switch function — lifts it to return a Promise<IResultOfT>.

Optional errorFn (when supplied) maps the caught exception to a typed error; without it the error type defaults to unknown — mirrors tryCatchAsync/fromPromise.

export function switchFnAsync<A, B, E = unknown>(
    f: (a: A) => B | Promise<B>,
    errorFn?: (error: unknown) => E,
): (a: A) => Promise<IResultOfT<B, E>>;

Defined in: adapters/switchFnAsync.ts

Example

import { switchFnAsync } from '@sandlada/result/adapters';
const safeFetch = switchFnAsync(async (url: string) => fetch(url).then(r => r.json()));
await safeFetch('https://api.example.com/data');

---

tee()

Side-effect on the one-track — calls f and returns the value unchanged. Unlike tap (which operates on the success track of a Result), tee operates on a plain value outside the railway.

Throw policy: Unlike railway tap, tee operates on a plain value with no failure state, so a throwing f propagates. Ensure f does not throw.

Wlaschin equivalent: tee (dead-end function)

export function tee<A>(f: (a: A) => void): (a: A) => A;

Defined in: adapters/tee.ts

Example

import { tee } from '@sandlada/result/adapters';
const logged = tee((x: number) => console.log('got:', x));
logged(42); // logs "got: 42", returns 42

---

teeAsync()

Async side-effect on the one-track — calls f and returns the value unchanged.

Throw policy: Unlike railway tap, teeAsync operates on a plain value with no failure state, so a throwing (or rejecting) f propagates. Ensure f does not throw.

export function teeAsync<A>(f: (a: A) => void | Promise<void>): (a: A) => Promise<A>;

Defined in: adapters/teeAsync.ts

Example

import { teeAsync } from '@sandlada/result/adapters';
const logged = teeAsync(async (x: number) => { console.log('got:', x); });
await logged(42); // returns 42 after the side effect

---

toOption()

Converts a Result to an Option. Ok(value) → Some(value), Err(_) → None. Discards the error information.

export function toOption<A, E>(r: IResultOfT<A, E>): IOption<A>;

Defined in: adapters/toOption.ts

Example

import { toOption } from '@sandlada/result/adapters';
import { ok, err } from '@sandlada/result/factories';
toOption(ok(42)); // Some(42)
toOption(err('boom')); // None