Look-and-say sequence

func lookandsay(str) {
    str.gsub(/((.)\2*)/, {|a,b| a.len.to_s + b })
}
 
var num = "1"
{
  say num;
  num = lookandsay(num)
} * 10

Output:

1
11
21
1211
111221
312211
13112221
1113213211
31131211131221
13211311123113112211