Hi.

The type of commandSender is:

(Serialize a, Serialize b) => a -> Handler (Maybe b)

But definition looks like this:

commandSender command reader writer = do ...

As I understund, command has type a and this function returns Handler (Maybe b). reader and writer doesn't fit here. What's going on?

Well, given this definition of commandSender taking three arguments, Handler must be a type synonym for a function type. Let's verify that: http://hackage.haskell.org/packages/archive/daemons/0.1.2/doc/html/Control-P... says:

type Handler r = Producer ByteString IO () -> Consumer ByteString IO () -> IO r

There you have your two extra arguments :) Cheers, Andres -- Andres Löh, Haskell Consultant Well-Typed LLP, http://www.well-typed.com