TypeScript Variadic Tuples for typing `promisify`

promisify.ts

type Tuple<T=any> = readonly T[]
type Nullable<T> = T extends null | undefined ? T : T | null | undefined
type ErrorFirstCallback<E extends Error, R> = (err: Nullable<E>, result: R) => void
type Resolve<R> = (value: R | PromiseLike<R>) => void
type Reject<E extends Error> = (reason: Nullable<E>) => void

function makeCallback<E extends Error, R>(resolve: Resolve<R>, reject: Reject<E>): ErrorFirstCallback<E, R> {
  return (error, result) => {
    if (error) reject(error) 
    else resolve(result) 
  }
}

export function promisify<Args extends Tuple, E extends Error, R>(fn: (...args: [...Args, ErrorFirstCallback<E, R>]) => void) { 
  return function promisifiedFn(...args: Args) {
    return new Promise<R>((resolve, reject) => {
      const cb = makeCallback<E, R>(resolve, reject)

      try {
        fn(...args, cb)
      } catch(e) {
        reject(e)
      }
    })
  }
}