[Haskell-cafe] generic putback

[Daniel Gorín]

I think you need to change the type of putback slightly:

import Data.IORef

putback :: a -> IO a -> IO (IO a)
putback a action =
   do next <- newIORef a
      return (do r <- readIORef next; writeIORef next =<< action; return r)

main =
   do getChar' <- putback 'a' getChar
      str <- sequence $ take 10 $ repeat getChar'
      putStrLn str

Thanks,
Daniel

On May 15, 2011, at 4:33 PM, Sergey Mironov wrote:

> Hi Cafe. I wonder if it is possible to write a IO putback function
> with following interface
> 
> putback :: a -> IO a -> IO a
> putback x io = ???
> 
> 
> where io is some action like reading from file or socket.
> I want putback to build new action which will return x on first call,
> and continue executing io after that.
> 
> Thanks in advance!
> Sergey.
> 
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