[Haskell-beginners] Type definition doesn't match with number of arguments

[Andres Löh]

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-Pipe-Socket.html#t:Handler

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