# Handling a failure in `match`

A `match` on a call handles its outcome: one arm for success, and one for
each failure the call can produce ([Match](match.md)):

```jadpo
function lookup_or_default(key: LookupCode) fails LookupRejected -> LookupResult {
    return match lookup(key) {
        success(value) -> value
        LookupMissing -> "not found"
        LookupRefused -> reject LookupRejected
    }
}
```

Every failure needs an arm, and there is no `_` for the rest. An arm can
recover with a value, as `LookupMissing` does here, map to another
failure with `reject`, or pass the failure on with `propagate`.

The arms handle only the call itself. A failure that leaves while the
call's arguments are worked out leaves the callable around the `match`, as
it would anywhere else.

The `match` errors, the `failure.outcome_*` rules, are listed on
[Logic](logic.md#errors).