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{ use vars qw( @cache @n ) }
{@cache = (0, 1)}
...
    {$cache [$n[-1]] ||= fib ($n[-1] - 1) + fib ($n[-1] - 2)}
    {return $cache[pop @n]}
}

{ use vars qw( @cache ) }
{@cache = (0, 1)}
...
        {return $cache[$n]}
    }
}

{ use vars qw( @cache ) }
sub fib {
...
        $n < 2 ? $n : $cache[$n] ||= fib ($n - 1) + fib ($n - 2)
    )
}