# Parser.OrElse

Runs the fallback parser from the original input when the first parser fails.

## Signatures

```ts
interface OrElse<P extends Any, Q extends Any> extends Parser<unknown> {
    readonly return: InputOf<this> extends infer Input extends string ? Apply<P, Input> extends infer R ? [
        R
    ] extends [
        never
    ] ? Pipe<Input, Q> : R extends readonly [
        infer Value,
        infer Rest extends string
    ] ? readonly [
        Value,
        Rest
    ] : never : never : never;
}
```

## Why

Alternatives do not leak partial consumption from a rejected branch.

## Ownership and lifetime

TypeScript instantiates `OrElse` while parsing a string-literal input; partial results and unconsumed text exist only in the resulting type.

## Property: return

Computes this type lambda's parse result for its current input.

## Property: return: Why

The local type-function protocol evaluates each parser combinator through this member without a parallel runtime object.

## Property: return: Ownership and lifetime

TypeScript evaluates `OrElse.return` when the surrounding parser is applied; the associated result is erased and retains no input at runtime.