> For AI agents: the complete documentation index is available at https://massaman.dev/llms.txt, the full documentation bundle is available at https://massaman.dev/llms-full.txt.

# orElse

Pass an `Err` error to a recovery function returning another `Result`. An `Ok` passes through unchanged, without calling recovery. Inspired by Rust's `Result::or_else`.

## Usage

### `orElse(result, recover)`

```typescript
import { err, ok, orElse, type Result } from 'massaman/control'

const primary: Result<string, TypeError> = err(new TypeError('Missing setting'))

const recovered = orElse(primary, (error) => ok(`Default: ${error.message}`))
// Ok('Default: Missing setting')

const failed = orElse(primary, () => err(new RangeError('No backup available')))
// Err<RangeError>; recovery can fail too.

orElse(ok('configured'), () => ok('fallback'))
// Original Ok('configured'); recovery is not called.
```

#### Parameters


resultResult<T, E>required

The result to recover. Its error is passed through without normalization.


recover(error: E) => Result<U, F>required

Called once on failure, or not at all on success. Must return a synchronous Result.

#### Returns

`Result<T | U, F>`. The original success or recovery Result is returned by reference. The original error type is replaced by the recovery error type, not automatically retained. To retain the original error, return `err(error)` from recovery.

#### Exceptions and async work

Unexpected recovery exceptions propagate; this helper is not a `try/catch`. Use `attempt` around throwing recovery work. Async callbacks are not accepted; use an explicit `isOk` guard when recovery needs to await a Promise.

## See also

- [`andThen`](https://massaman.dev/reference/control/andThen.md) — continue on success instead
- [`unwrapOr`](https://massaman.dev/reference/control/unwrapOr.md) — extract a plain value with a default
- [Result & Errors](https://massaman.dev/concepts/result.md)