Result type for Typescript, sorta like rust.

typescript-result.ts

type Result<Ok, Err extends Error = Error> = 
  | { kind: 'ok', value: Ok }
  | { kind: 'err', err: Err }

const Ok = <T>(value: T): Result<T> => {
  return {
    kind: 'ok',
    value
  }
}

const Err = <E extends Error = Error>(err: E): Result<never, E> => {
  return {
    kind: 'err',
    err
  }
}

type AnyFunction = (...args: any[]) => any

type Safely<F extends AnyFunction> =
  (...args: Parameters<F>) => Promise<Result<Awaited<ReturnType<F>>>>

function safely<F extends AnyFunction>(fn: F): Safely<F> {
  return async (...args) => {
    try {
      return Ok(await fn(...args))
    } catch (err) {
      return Err(err instanceof Error ? err : new Error(`uncaught ${err}`))
    }
  }
}

async function mayFail() {}

const safelyMayFail = safely(mayFail)

;(async () => {
  const result = await safelyMayFail()
  if (result.kind === 'ok') {
    // result.value is mayFail's return value
  } else {
    // result.err is the Error object
  }
})()