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Today's Topics:
1. Type definition doesn't match with number of arguments
(Emanuel Koczwara)
2. Re: Type definition doesn't match with number of arguments
(Andres L?h)
----------------------------------------------------------------------
Message: 1
Date: Wed, 08 May 2013 23:05:47 +0200
From: Emanuel Koczwara <[email protected]>
Subject: [Haskell-beginners] Type definition doesn't match with number
of arguments
To: [email protected]
Message-ID: <1368047147.10660.7.camel@emanuel-laptop>
Content-Type: text/plain; charset="UTF-8"
Hi,
Please help me understund this code:
http://hackage.haskell.org/packages/archive/daemons/0.1.2/doc/html/src/Control-Pipe-C3.html#commandSender
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?
Emanuel
------------------------------
Message: 2
Date: Wed, 8 May 2013 23:59:12 +0200
From: Andres L?h <[email protected]>
Subject: Re: [Haskell-beginners] Type definition doesn't match with
number of arguments
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Message-ID:
<CALjd_v5o=yrQYzXC4iELkGgooz9GU+cZWt=6crz0rqafqyl...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
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 L?h, Haskell Consultant
Well-Typed LLP, http://www.well-typed.com
------------------------------
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