Hello, I need to be able to use strict bytestrings to efficiently build a lazy bytestring, so I'm using putByteString in Data.Binary. But I also need random numbers, so I'm using mwc-random. I end up in the "IO Put" monad, and it's giving me some issues. To build a random document, I need a random length, and a collection of random words. So I have docLength :: IO Int word :: IO Put Oh, also putSpace :: Put My first attempt: doc :: IO Put doc = docLength >>= go where go 1 = word go n = word >> return putSpace >> go (n-1) Unfortunately, with this approach, you end up with a one-word document. I think this makes sense because of the monad laws, but I haven't checked it. Second attempt: doc :: IO Put doc = docLength >>= go where go 1 = word go n = do w <- word ws <- go (n-1) return (w >> putSpace >> ws) This one actually works, but it holds onto everything in memory instead of outputting as it goes. If docLength tends to be large, this leads to big problems. Oh, yes, and my main is currently main = L.writeFile "out.txt" =<< fmap runPut doc This needs to be lazier so disk writing can start sooner, and to avoid eating up tons of memory. Any ideas? Thanks! Chad