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devexamples

Typed Result Type Instead Of Throwing

A Result union with map, mapErr and andThen combinators that makes error paths explicit and compiler-checked instead of exception driven.

TypescriptForm Validation

Code

export type Result<T, E> =
  | { readonly ok: true; readonly value: T }
  | { readonly ok: false; readonly error: E };

export function ok<T>(value: T): Result<T, never> {
  return { ok: true, value };
}

export function err<E>(error: E): Result<never, E> {
  return { ok: false, error };
}

export function map<T, U, E>(result: Result<T, E>, fn: (value: T) => U): Result<U, E> {
  return result.ok ? ok(fn(result.value)) : result;
}

export function mapErr<T, E, F>(result: Result<T, E>, fn: (error: E) => F): Result<T, F> {
  return result.ok ? result : err(fn(result.error));
}

export function andThen<T, U, E>(
  result: Result<T, E>,
  fn: (value: T) => Result<U, E>,
): Result<U, E> {
  return result.ok ? fn(result.value) : result;
}

export function unwrapOr<T, E>(result: Result<T, E>, fallback: T): T {
  return result.ok ? result.value : fallback;
}

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