On Wed, 28 Jul 2010, Darren Duncan wrote:
> I think that a general solution here is to accept that there may be more
> than one valid way to sort some types, strings especially, and so
> operators/routines that do sorting should be customizable in some way so
> users can pick the behaviour they want.
> The customization could be applied at various levels, such as using an
> extra argument or trait for the operator/function that cares about
> ordering,

That much I agree wholeheartedly with, but ...

> or by using an extra attribute or trait for the types being sorted.

... puts us back where we started: how do we cope if the two endpoints
aren't tagged with the same attribute or trait or locale?

In any case I'd much rather prefer that the behaviour be lexically scoped,
with either adverbs or pragmata, not with the action-at-a-distance that's
caused by tagging something as fundamental as a String.

Yes sometimes you want the behaviour of your range to mimic the locale of
its operands, but then it should be explicit, with a trait that also
explicitly selects either the left or right operand to extract the locale
from. And probably throw an exception if they aren't in the same locale.

If you don't specify that you want locale-dependent behaviour then the
default action should be an unthrown exception unless both endpoints are
inarguably comparable, so IMHO that pretty much rules out any code-points
that are used in more than language, save perhaps raw ASCII. And even then
you really should make an explicit choice between case-sensitive and
case-insensitive comparison.

> When you want to be consistent, the behaviour of "cmp" affects all of the
> other order-sensitive operations, including any working with intervals.

Indeed, the range constructor and the cmp operator should have the same
adverbs and share lexical pragmata.

> So then, "a" cmp "ส้" is always defined, but users can change the
> definition.

I take the opposite approach; it's always undefined (read, unthrown
exception) unless the user tells us how they want it treated. That can be a
command-line switch if necessary.

To paraphrase Dante, "the road to hell is paved with Reasonable Defaults".
Or in programming terms, your reasonable default is the cause of my ugly


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