[Haskell-cafe] Why not some subclass of Floating to model NaNs as some handleable bottom?

Michal J Gajda mgajda at mimuw.edu.pl
Wed Aug 4 13:11:05 UTC 2021

Dear Yue,

Bottom has much weaker semantics than an exception: it means You may
never get a result and thus will never handle it!

Another reason is convenience: it is frequently the case that giving
NaN in a row of numbers is much more informative than crashing a
program with an exception and never printing the result anyway.

Finally IEEE special values have clear propagation semantics: they are
basically Maybe on steroids.

The problem with this approach is indeed a silent handling.

But in order to fix this, it is better to add preconditions to
specific algorithms that do not allow IEEE special value on input
(`isFinite` or `isNotNaN`) and then track the origin of the special
value with the methods like those described here:

Never throw an error without telling exactly why it happened and
exactly where to fix it :-). Using bottom is last resort; exceptions

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