Re: [Haskell-cafe] Lazy IO with recursive reads?

24 Feb 2010

      Hi Fabian

You need to yield with unsafeInterleaveIO to allow some of the list to
be be consumed.

Something like this (which never terminates of course, but do produce output):

import System.IO.Unsafe
import Control.Monad

main = do messages <- readLazy
          mapM_ (\x -> putStr $ show x ++ "\n") $ messages
          return ()
          where
            readLazy :: IO [String]
            readLazy = unsafeInterleaveIO $ do
                         { c <- fancyIORead
                         ; liftM2 (++) (return c) readLazy
                         }
            fancyIORead :: IO [String]
            fancyIORead = return ["aa","bb"]

Re: [Haskell-cafe] Lazy IO with recursive reads?

Stephen Tetley