// Old mdo
import "Prelude"

main = mdo 
  x <- [1,2]
  return $ print "\(x :: Integer)"
--
1
2
[(), ()]
--
// New mdo
module {
    features = [edo]
}
import "Prelude"

main = mdo 
  x <- [1,2]
  return $ print "\(x :: Integer)"
--
9:12-9:35: No side-effects allowed here.