Proposal: Add sequenceWhile and SequenceWhile_ to Control.Monad

[Dominic Steinitz]

I'm not sure of the protocol for adding things to existing libraries but I'd 
like to propose the addition of these two functions to Control.Monad.

sequenceWhile_ :: Monad m => (a -> Bool) -> [m a] -> m ()
sequenceWhile_ _ [] =
  return ()
sequenceWhile_ p (x:xs) =
  x >>= \c -> if (p c) then sequenceWhile_ p xs else return ()

sequenceWhile :: Monad m => (a -> Bool) -> [m a] -> m [a]
sequenceWhile _ [] =
  return []
sequenceWhile p (x:xs) = do
  y <- x
  if (p y)
    then do
      ys <- sequenceWhile p xs
      return (y:ys)
    else
      return [y]