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):

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.