On 03/09/10 11:11, Henning Thielemann wrote:
Ivan Lazar Miljenovic schrieb:
On 3 September 2010 04:57, Arie Peterson <ar...@xs4all.nl> wrote:
On Thu, 2 Sep 2010 19:30:17 +0200, Daniel Fischer
<daniel.is.fisc...@web.de> wrote:
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.
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