Are you sure you want to execute last only when $has_even = 1 is true? Using "and" would be confusing if you decide later to refactor the code and suddenly end up with

    $_ % 2 and $has_odd = 0 and last;
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or maybe the second "and" would be turned to "or", but it would be confusing anyway.

More idiomatic way of writing this would be

$_ % 2 or $has_even = 1, last;
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if you insisted on using no if/unless. I'd probably use

$has_even = 1, last unless $_ % 2;
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but YMMV.

Update: s/if/unless/. Thanks Athanasius.