[Haskell-cafe] Phantoms

Jules Bean jules at jellybean.co.uk
Fri Aug 15 02:00:54 EDT 2008

Malcolm Wallace wrote:
> Andrew Coppin <andrewcoppin at btinternet.com> wrote:
>>> instnace Show (Foo Int) ...
>>> instnace Show (Foo Double) ...
>> ...WHY did I not think of this myself? o_O
> Because it is not Haskell'98?  
> It requires {-# LANGUAGE OverlappingInstances #-}

No it doesn't?

It requires the much more semantically simple -XFlexibleInstances, as 
far as I know.

Overlapping would only be needed if there was also a polymorphic 
instance on Foo a?


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