Using Ord for keys of maps and sets
gale at sefer.org
Mon Dec 3 09:04:09 EST 2007
>> We could allow for case 3 by not providing any default
>> instances for Indexable.
Henning Thielemann wrote:
> This would obstruct 'start GHCi and play around' sessions, since you
> cannot create a set of something on the fly. (However, GHCi could still be
Yes. I am suggesting also leaving the current versions
that use Ord, so we are no worse off with that than we
were before, at least.
> Still, later in the above thread, Johannes Waldmann throws in Local
Ah, yes. That would be great! I would especially like it
for GHCI - in general, not just because of the special case you
But this has come up before. There are people who
are not sure about this feature, because of
some ambiguous and/or confusing cases that can
come up when you redefine an instance that already
exists in an enclosing context.
And anyway - this is a serious language change.
It will at best take time. Your Indexable class could
be used right now to make a lot of the most common
cases much easier to handle.
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