RE: [Haskell-cafe] newbie type signature question

Brian Hulley wrote:

There was a post a while back (unfortunately I can't seem to locate it) where someone posted a link to some guidelines on haskell coding style where one guideline was never to use contexts in data declarations.

I would love to see that guideline. What is the correct way to express a constraint for a data declaration if this way is wrong? Thanks, Brock