result

result.ts

export class UnhandledError extends Error {
	originalError: unknown;
	constructor(originalError: unknown) {
		super('Unhandled error');
		this.originalError = originalError;
		this.name = 'UnhandledError';
	}
}

type AttemptSuccess<T> = readonly [null, T];
type AttemptFailure<E> = readonly [E, null];
type AttemptResult<E, T> = AttemptSuccess<T> | AttemptFailure<E>;
export type AttemptResultAsync<E, T> = Promise<AttemptResult<E, Awaited<T>>>;

export const result = {
	fn: <const E, const R>(fn: (...args: any) => AttemptResult<E, R>): AttemptResult<E | UnhandledError, R> => {
		try {
			return fn();
		} catch (error) {
			return result.err(new UnhandledError(error));
		}
	},
	fnAsync: async <const E, const R>(
		fn: (...args: any) => AttemptResultAsync<E, R>,
	): AttemptResultAsync<E | UnhandledError, R> => {
		try {
			return await fn();
		} catch (error) {
			return Promise.resolve(result.err(new UnhandledError(error)));
		}
	},
	ok: <const R>(success: R): AttemptSuccess<R> => [null, success],
	err: <const E>(error: E): AttemptFailure<E> => [error, null],
};

/** Examples */
  
const [error, data] = result.fn((a: number, b: number) => {
	if (b === 0) return result.err('Cannot divide by zero');
	return result.ok(a / b);
});
if (error) {
	console.log('you got', error);
	//                      ^? "Cannot divide by zero" | UnhandledError
	if (error instanceof UnhandledError) {
            console.log('something really unexpected happened');
	} else {
            console.log('couldnt divide because', error);
		//                                 ^? "Cannot divide by zero"
	}
} else {
	console.log('you got', data);
	//                      ^? number
}

const [error2, data2] = await result.fnAsync(async (a: number, b: number) => {
	if (b === 0) return result.err('Cannot divide by zero');
	return result.ok(a / b);
});
if (error2) {
	console.log('you got', error2);
        //                      ^? "Cannot divide by zero" | UnhandledError
} else {
	console.log('you got', data2);
	//                      ^? number
}