check for exhaustive patterns is broken

[Feliks Kluzniak]

> A somewhat prettier solution would maybe be to use Ord.compare:

> case (compare k k') of LT -> ... ; GT -> ... ; EQ -> ...

Thanks, I did consider this one, but it did not seem too pretty to me.  All in
the eye of the beholder, of course.

> This might even be faster if comparison is expensive.

Hm, you might have a point.  I tend to more or less forget about lower-level
speed issues when programming in Haskell, which is quite a relief (!) and still
leads to good result.

-- F. K.