Re: Motion to finalise interval literals
Richard and P1788
On 9 Jun 2013, at 01:27, Richard Fateman wrote:
> On 6/8/2013 6:32 AM, John Pryce wrote:
>> Jürgen and P1788
>>
>> On 7 Jun 2013, at 19:02, Jürgen Wolff von Gudenberg wrote:
>>> as already stated in one of my last emails, I think interval literals should not be required. They will involve languages and compilers, and ,hence, augment the workload in dissemination the of standard.
>>>
>>> so change the "shall" into a "should"
>> With respect, I disagree entirely with this and wonder if the draft text doesn't make the purpose of interval literals (ILs) clear enough.
>>
>> - For some time to come, interval computation will not be integrated
>> within a language; Sun Fortran & C++ are an exception.
>> Instead it will be provided by a bolt-on library. Interval literals
>> give a standard specification for reading (especially) and writing
>> intervals -- important both for interactive work and for reading/
>> writing text files.
> I think that I differ in my view of what the standard is aiming for...
I find your arguments quite strong and am more inclined to make interval literals (ILs) optional. But do you and Jürgen intend
- text2interval "should" be provided, and if it is, it *shall* accept
the stated syntax & semantics?
or
- text2interval "shall" be provided, and *should* accept the stated
syntax & semantics? If it doesn't, I suppose it accepts the host
language's syntax & semantics of intervals.
or some other variant?
However:
On 9 Jun 2013, at 01:27, Richard Fateman wrote:
>> Whichever, I continue to say that to conform, the implementation needs
>> either to implement text2interval() or to embed its syntax+semantics
>> of intervals within the language.
> I'm not sure I understand this. If I can construct any interval whatsoever with
> containment guaranteed (or tightness guaranteed) by constructing A, B and [A,B],
> does that mean I have embedded enough to conform?
Probably, but I'll have to think more about it. I pass over it for now.
> While I take issue with
> 0.1 and "0.1" having different meanings, a program to parse "0.1" as
> 1/10 is just a few lines in Lisp. I am not objecting to doing the computation,
> just that it has, in Lisp, nothing to do with intervals.
Do you take issue with Sun Fortran? If I understand right, in
real x
interval xx
x = 0.1 !machine approximation
xx = [0.1] !enclosure of exact value
the two 0.1's have "different meanings" in your sense. You don't like 0.1 changing its meaning when you put string quotes round it, so what about when you put square brackets round?
John