Executable library

Library saved as Hailstone.sm

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}"
}

It can be run with:

$ sidef Hailstone.sm

It can then be used with a program such as:

include Hailstone
 
var score = Hash()
100_000.times { |i| score{ Hailstone::hailstone(i).len } := 0 ++ }
 
var k = score.keys.max_by {|k| score{k} }
say "Most common length is #{k}, occurring #{score{k}} times"

Called with a command line as:

$ sidef test_hailstone.sf

The library is searched in the directories specified in the SIDEF_INC environment variable, which defaults to the current directory.