Last Friday of each month

require('DateTime')
var (year=2016) = ARGV.map{.to_i}...
 
for month (1..12) {
   var dt = %O<DateTime>.last_day_of_month(year => year, month => month)
   while (dt.day_of_week != 5) {
      dt.subtract(days => 1)
   }
   say dt.ymd
}

Output:

$ sidef lastfriday.sf 2012
2012-01-27
2012-02-24
2012-03-30
2012-04-27
2012-05-25
2012-06-29
2012-07-27
2012-08-31
2012-09-28
2012-10-26
2012-11-30
2012-12-28