[Haskell-cafe] Lazy IO with recursive reads?

Fabian Roth fabian.roth at gmail.com
Wed Feb 24 08:53:32 EST 2010

Hi all,

I am trying to read structured data from a socket and return a lazy list of
records. However, the socket reading operation seems to be strict and never
returns (until stack overflow). Here's some simplified code to reproduce the


import Control.Monad

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


In my implementation fancyIORead reads blocks from the socket and returns a
list of records.
But it seems readLazy doesn't ever return.

What could be the problem here?

Also, if anyone has a better solution to write this thing, pls let me know.

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