Re: [Haskell-beginners] System.USB.writeInterrupt -- confused by error message from type system

Hi Sean, I think that your function for testing board should look like this: testBoard :: Device -> DeviceHandle -> IO () testBoard dev handle = do putStrLn $ "Inspecting device: \"" ++ (show dev) ++ "\"\n" -- write 0x00 0x00 0x00 0x00, get back same... let payload = pack "\x00\x00\x00\x00" let endPoint = EndpointAddress 0 Out let action = writeInterrupt handle endPoint (size, status) <- action payload 1000 return () You need to use let because writeInterrupt returns (Timeout -> ByteString -> IO (Size, Bool)) instead of IO (Timeout -> ByteString -> IO (Size, Bool)) Karol