Re: [Haskell-cafe] Re: Tail Recursion within the IO Monad

On Thu, May 17, 2007 at 11:22:34AM +0100, Simon Marlow wrote:

sequence still isn't tail-recursive, although sequence_ is. If you want a tail-recursive sequence, the only way to do it is like this:

sequence' :: [IO a] -> IO [a] sequence' ms = do let as = map unsafePerformIO ms foldr seq (return ()) as return as

sequence :: Monad m => [m a] -> m [a] sequence ms = reverse `liftM` sequence' [] ms sequence' l [] = return l sequence' l (m:ms) = m >>= \x -> sequence' (x:l) ms Stefan