Re: [Haskell-cafe] Unnecessarily strict implementations

On 03/09/10 11:11, Henning Thielemann wrote:

Ivan Lazar Miljenovic schrieb:

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On 3 September 2010 04:57, Arie Peterson wrote:

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On Thu, 2 Sep 2010 19:30:17 +0200, Daniel Fischer wrote:

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Why would one consider using Ord for Map an abuse? A kludge, for performance reasons, but an abuse? Because it forces one to declare Ord instances for types which have no natural ordering. It is useful to *not* have such instances, in order to catch programming errors.

What precisely do you mean by natural ordering?

E.g. I wanted to have a Set of Gaussian (complex) integers, but I did not want to define an Ord instance for them, because writing a < (b :: Gaussian) is a bug with high probability.

Isn't this what newtype is good for? Instead of declaring Ord Gaussian to get Set Gaussian and risking the bug you describe, create newtype GaussianInSet = G Gaussian, declare Ord GaussianInSet and use Set GaussianInSet. Thanks, Neil.