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Re: An error-catching question

Ian McIntosh wrote:

There's no point having undecorated intervals unless users can get correct
answers with them.  The purpose of decorations is to add more information
about why value is what it is.
And the purpose of undecorated intervals is to drop that information when users do not need them because they know that all values will either be free of the exceptions covered by decorations, or that these exceptions do not matter. 

There are a host of such cases; indeed it is likely to be the vast
majority.



All "values" including non-values like NaI
need to be represented somehow in undecorated intervals.  So there has to
be an undecorated representation for Not An Interval, and a constructor
that can produce it.


This does not follow. Undecorated intervals are provided precisely
because one can assume that the inputs and results will be meaningful
by construction of the code where it is used.
Therefore, undecorated intervals can always be standard intervals (sets), and stripping an invalid or otherwise NaI-decorated interval 
can simply give EMPTY.




I think that a constructor should always produce a decorated interval,
and the programmer cvan then decide to throw away the decoration,
if desired (after querying the result, if needed).




Arnold Neumaier