[Haskell-beginners] Re: how to define a user datatype consisting of instances of String?

[Benjamin L.Russell]

On Thu, 23 Oct 2008 18:39:52 +0900, Benjamin L. Russell
<DekuDekuplex at Yahoo.com> wrote:

>instance Show Wine where 
>    show (Red Merlot) = "Merlot"
>    show (Red Syrah) = "Syrah"
>    show (Red Port) = "Port"
>    show (White SauvignonBlanc) = "Sauvignon Blanc"
>    show (White Riesling) = "Riesling"
>    show (White PinotNoir) = "Pinot Noir"
>
>instance Show Red where
>    show Merlot = "Merlot"
>    show Syrah = "Syrah"
>    show Port = "Port"
>
>instance Show White where
>    show SauvignonBlanc = "Sauvignon Blanc"
>    show Riesling = "Riesling"
>    show PinotNoir = "Pinot Noir"

The only remaining issue is whether there is a way to define the type
constructor for Wine without pre-defining parts that are later defined
in the type constructors for Red and White.

In the above code, for example, 

>instance Show Wine where 
>    show (Red Merlot) = "Merlot"

essentially pre-defines the following definition later given in the
type constructor for Red:

>instance Show Red where
>    show Merlot = "Merlot"

This seems redundant.

Since the type definition for Wine is 

data Wine = Red Red | White White

the type constructors for Red and White both require an argument, so 

show (Red Merlot) = ...

seems reasonable.

This would seem to imply that if I need to reduce redundancy, I should
probably rewrite the RHS of the above line.

Is there a way to refer to the type constructors for Red and White in
the type constructor for Wine?

-- Benjamin L. Russell