[Haskell-cafe] Typeclasses and instances

Benjamin Franksen benjamin.franksen at bessy.de
Thu Mar 17 15:33:01 EST 2005

On Thursday 17 March 2005 20:57, Mark Carroll wrote:
> Another note, with more help from friends:
> It turns out that GHC 6.4 will let me do,
> 	newtype Floating a => Test a = Test [a] deriving Show
> 	x = Test [False, True]
> but, if I change "newtype" to "data", it then says,
> 	No instance for (Floating Bool)
> I'm not sure I quite understand what's going on.

This looks like a bug to me. Regardless of whether Test is defined via 'data' 
or 'newtype', the definition of 'x' should not be accepted (assuming there is 
no 'instance Floating Bool' in scope).


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