Proposal: Bounded instance for IntSet (ticket #1953)

[Henning Thielemann]

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On Mon, 3 Dec 2007 kahl at cas.mcmaster.ca wrote:

> On Sun, 2 Dec 2007, at 23:53:36 +0000, Ross Paterson wrote:
>  >
>  > On Sun, Dec 02, 2007 at 03:45:40PM -0800, David Benbennick wrote:
>  > > I propose to add a Bounded instance to IntSet.hs.
>  > >
>  > > IntSet is in Ord, and there are only finitely many instances of
>  > > IntSet. Therefore there is a min IntSet and a max IntSet. It turns out
>  > > these bounds are very simple:
>  > >
>  > > instance Bounded IntSet where
>  > >     minBound = empty
>  > >     maxBound = singleton maxBound
>  >
>  > These are the minimum and maximum under the Ord instance (also for Set),
>  > but what is the intuition behind that ordering?
>
> In my opinion, the class ``Ord'' is not particularly heavy on intuition;
> it just provides an interface to ``the standard linear ordering''
> for each of its types,
> so that these types can be used for keys in Data.Map's, etc.
>
> Not many types are naturally understood as linearly ordered,
> but most of those types should still be usable for keys in maps.

I already told about by scepticism about using Ord for keys of maps and
sets:
  http://www.haskell.org/pipermail/libraries/2007-April/007411.html