[Haskell-cafe] Why does Enum succ and pred functions throw exception

[Alexander Solla]

On Thu, Jun 21, 2012 at 5:36 PM, Richard O'Keefe <ok at cs.otago.ac.nz> wrote:

It always struck me as odd that Enum doesn't extend Ord.
> There's a reason given for not having Bounded extend Ord,
> which doesn't really apply to a class having fromEnum :: a -> Int.
> Testing whether an enum bound is at a limit is thus a bit tricky.


An ordering does not typically induce a computable enumeration.  For
example, there are infinitely many rationals between any pair of rationals.
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