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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