[Haskell-cafe] Defining methods generically for a class

Martijn van Steenbergen martijn at van.steenbergen.nl
Thu Jan 8 12:26:14 EST 2009

Hi Jeff,

Jeff Heard wrote:
> instance Region a => Eq a where
>   regiona == regionb = all $ zipWith (==)  (bounds regiona) (bounds regionb)

If you want to be Haskell98 compliant, why not define regionEquals :: 
Region a => a -> a -> Bool as above and use that everywhere instead of (==)?

If you insist on using the overloaded (==), then in Haskell98 you will 
need to define individual Eq instances for all your custom region types. 
However, you can simply define (==) = regionEquals for all those types.

Hope this helps,


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