@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, plus lazy AsyncResult / AsyncOption thunks
• Railway Oriented Programming built-in — map, bind, orElse, match, tap, combine
• Reliability — bounded retry, timeout, race, any, allSettled for production pipelines
• Observability — breadcrumb withPath / ctx / tapErrContext + format / inspect / installObserver
• 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

The main barrel @sandlada/result is type-focused. Its only runtime value is moduleMarker, used to materialize the entry and sourcemap; functional runtime values come from dedicated subpath packages — pick the one that matches your shape.

import type { IResultOfT } from '@sandlada/result';              // type contracts
import { ok, err } from '@sandlada/result/factories';             // core constructors
import { map, unwrapOr } from '@sandlada/result/operators';       // sync operators
import { pipe } from '@sandlada/result/composition';              // pipe / composeK / safeTry

// 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'),
);

Why subpath imports? @sandlada/result exposes many types — IResultOfT, IOption, AsyncResult, AsyncOption. Names like map, bind, match exist for both IResultOfT and IOption. The compiler can't disambiguate; the package layout does. Subpath imports make the type explicit at the call site and keep tree-shaking total. See ARCH.md ADR 10.

:ledger: API Overview

All exports are listed in SPEC.md with links to their source files. Full type signatures and JSDoc live in the source.

| Export path | Contents | | --- | --- | | @sandlada/result | Type-focused barrel — IResult, IResultOfT, IOption, AsyncResult, AsyncOption, plus the runtime moduleMarker. Functional runtime values must use a subpath. | | @sandlada/result/factories | Core constructors (ok, err, asyncOk, asyncErr, tryCatch, fromPromise, …). | | @sandlada/result/operators | Sync operators on IResultOfT (map, bind, match, pipe, …). | | @sandlada/result/option | Sync IOption<T> operators (ofSome, ofNone, map, bind, okOr, transpose, …). | | @sandlada/result/async-result | Lazy AsyncResult<T, E> thunk operators. | | @sandlada/result/async-option | Lazy AsyncOption<T> thunk operators. | | @sandlada/result/promise-result | Eager async operators on Promise<IResultOfT>. | | @sandlada/result/promise-option | Eager async operators on Promise<IOption>. | | @sandlada/result/composition | pipe, composeK, safeTry, pipeAsync, composeKAsync. | | @sandlada/result/adapters | toOption, fromOption, switchFn, liftMap, tee, … | | @sandlada/result/combine | combine, combineWithAllErrors, all. | | @sandlada/result/reliability | retry, retryLazy, timeout, race, any, allSettled. | | @sandlada/result/observability | ctx, withPath, format, inspect, installObserver, … | | @sandlada/result/primitives | cond, condErr, sequence, reduce, partitionOption, lift. | | @sandlada/result/types | Same type contracts as the main barrel, plus its own runtime moduleMarker. Kept for backward compatibility. |

:package: Integration Pattern

Bind your error type once and eliminate generic boilerplate:

// app-result.ts
import { ok, err } from '@sandlada/result/factories';
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 — API index with links to each source file
• ARCH.md — internal architecture and contributor documentation
• AGENTS.md — AI agent conventions and project metadata for tool-assisted development

License

MIT