func hailstone(n) {
    gather {
        while (n > 1) {
            take(n)
            n = (n.is_even ? (n/2) : (take(3*n + 1)/2))
        }
        take(1)
    }
}

if (__FILE__ == __MAIN__) {             # true when not imported
    var seq = hailstone(27)
    say "hailstone(27) - #{seq.len} elements: #{seq.first(4)} [...] #{seq.last(4)}"

    var n = 0
    var max = 0
    100_000.times { |i|
        var seq = hailstone(i)
        if (seq.len > max) {
            max = seq.len
            n = i
        }
    }

    say "Longest sequence is for #{n}: #{max}"
}