@sandlada/result

@sandlada/result is a TypeScript library implementing the Result pattern — a type-safe, exception-free approach to error handling. It makes error flows explicit in the type system so you never wonder whether a function can fail.

Unlike traditional Result libraries that hardcode a single error type, @sandlada/result is fully generic: you bring your own error shapes (discriminated unions, classes, or plain objects).

:zap: Highlights

• Fully generic TError — define your own error types
• Pure FP — data-last curried operators (pipe, map, bind) with discriminated union types
• Option type — IOption<T> (Some / None) with curried operators
• Async-native — asyncOk/asyncErr factories + pipeAsync for Promise-based railways
• Railway Oriented Programming built-in — map, bind, orElse, match, tap, combine
• JSON serializable — result and option objects survive JSON.stringify
• Zero dependencies
• ESM-only, strict TypeScript
• Inspired by the C# Result pattern and Rust's Option<T>

:eyes: Installation

npm i @sandlada/result

ESM only. This package cannot be used with require(). Your project must use ESM (import) or dynamic import().

:ship: Quick Start

import { ok, err, pipe, map, bind, unwrapOr } from '@sandlada/result';
import type { IResultOfT } from '@sandlada/result';



// Define your error type (discriminated union recommended)
type AppError =
  | { kind: 'NotFound'; id: string }
  | { kind: 'Validation'; fields: Record<string, string> };

function getUser(id: string): IResultOfT<User, AppError> {
  if (!id) {
    return err<AppError>({ kind: 'Validation', fields: { id: 'Required' } }) as IResultOfT<User, AppError>;
  }
  const user = db.find(id);
  if (!user) {
    return err<AppError>({ kind: 'NotFound', id }) as IResultOfT<User, AppError>;
  }
  return ok(user);
}

// FP curried style
const name = pipe(
  getUser('42'),
  map(u => u.name),
  unwrapOr('Unknown'),
);

:ledger: API Overview

All exports are documented in detail in SPEC.md with full signatures, examples, and edge-case behavior.

| Export path | Contents | | ------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | @sandlada/result | Core types (IResult, IResultOfT), factories (ok, err, tryCatch, fromPromise, …), sync operators (map, bind, match, unwrap, orThrow, …), async operators (mapAsync, bindAsync, pipeAsync, …), adapters (toOption, switchFn, tee, …), composition (pipe, composeK, safeTry), combine (combine, all, combineWithAllErrors) | | @sandlada/result/async | Async operators on Promise<IResultOfT> — mapAsync, bindAsync, matchAsync, orElseAsync, tapAsync, unwrapOrAsync, asyncAndThrough, … | | @sandlada/result/async-result | Lazy AsyncResult thunks — from, fromPromise, fromResult, map, andThen, orElse, match, combine, combineWithAllErrors | | @sandlada/result/adapters | Wlaschin three-shape adapters — switchFn, liftMap, tee, toOption, fromOption | | @sandlada/result/combine | Parallel combination — combine, all, combineWithAllErrors | | @sandlada/result/composition | Composition helpers — pipe, composeK, safeTry, pipeAsync | | @sandlada/result/factories | Core constructors — ok, err, fromPredicate, fromThrowable, tryCatch, fromPromise | | @sandlada/result/operators | Sync operators — map, bind, match, unwrap, orThrow, separate, traverseArray, … | | @sandlada/result/option | Option module — ofSome, ofNone, map, andThen, match, okOr, transpose, … | | @sandlada/result/types | Type definitions only — IResult, IResultOfT, IOption, AsyncResult |

:package: Integration Pattern

Bind your error type once and eliminate generic boilerplate:

// app-result.ts
import { ok, err } from '@sandlada/result';
import type { IResultOfT } from '@sandlada/result';
import type { AppError } from './errors.js';

export type AppResult<T = void> = IResultOfT<T, AppError>;

export const AppResult = {
  Success<T>(value?: T): AppResult<T> { return (value === undefined ? ok() : ok(value)) as unknown as AppResult<T>; },
  Failure(error: AppError): AppResult<never> { return err(error) as unknown as AppResult<never>; },
} as const;

// usage — no TError generic anywhere
function getUser(id: string): AppResult<User> {
  if (!id) return AppResult.Failure({ kind: 'Validation', fields: { id: 'Required' } });
  return AppResult.Success({ id, name: 'Alice' });
}

:ledger: Further Reading

• SPEC.md — complete API reference with signatures, examples, and all modules
• ARCH.md — internal architecture, module design, and contributor documentation
• AGENTS.md — AI agent conventions and project metadata for tool-assisted development

License

MIT