[Haskell-cafe] Existentially-quantified constructors, Eq and Show

Greg Buchholz haskell at sleepingsquirrel.org
Wed Dec 7 19:08:10 EST 2005

Joel Reymont wrote:
> Folks,
> Is there a less verbose way of doing this:
> data State a
>     = Start
>     | Stop
>     | (Show a, Eq a) => State a

   I'm curious, what is the difference between the above and...

        data State a = Start 
                     | Stop  
                     | State a  deriving (Show, Eq)
...Does it give better error messages at compile time or something?


Greg Buchholz

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