Action Item QT4CG-004-02: DN to make a proposal for deep-equal-safe for future discussion ( Re: Draft minutes for QT4CG meeting 004, 2022-09-27)

On Tue, Sep 27, 2022 at 9:42 AM Norm Tovey-Walsh <norm@saxonica.com> wrote:

>
>
> Draft Minutes
>
> Summary of new and continuing actions [0/7]
>
>      * [ ] QT4CG-002-01: NW to incorporate email feedback and produce new
>        versions of the process documents.
>      * [ ] QT4CG-003-03: NW to tweak the CSS for function signatures to
> avoid
>        line breaks on - characters.
>      * [ ] QT4CG-002-10: BTW to coordinate some ideas about improving
>        diversity in the group
>      * [ ] QT4CG-004-01: MK (with DN and RD) to draft a new proposal for
>        variadic functions
>      * [ ] QT4CG-004-02: DN to make a proposal for deep-equal-safe for
> future
>        discussion
>      * [ ] QT4CG-004-03: MK to draft a pull request implementing
>        fn:intersperse
>      * [ ] QT4CG-004-04: DN to open an issue for the inverse of
>        fn:intersperse
>
>
The description of the function *fn:deep-equal-safe*() is in a pdf file
that can be found here:


*https://github.com/dnovatchev/FXSL-XSLT2/blob/master/fn-deep-equal-safe.pdf
<https://github.com/dnovatchev/FXSL-XSLT2/blob/master/fn-deep-equal-safe.pdf>*
Note: this document is essentially a compilation from the FO 3.1 of:
      *op:same-key*  (
https://www.w3.org/TR/xpath-functions-31/#func-same-key),  and
      *fn:deep-equal *(
https://www.w3.org/TR/xpath-functions-31/#func-deep-equal)

Special care was taken to substitute the fn:deep-equal semantics that
either results in raising an error, or in possible intransitivity or
context-dependency. All such behavior has been substituted with the
corresponding behavior from *op:same-key*, which the 3.1 Spec claims to be:
"*deterministic, context-independent, and ·focus-independent*", etc.

More specifically, to achieve this:


   1. No errors are raised, instead *false() *is returned

   2. Strings are compared without any dependency on collations
(*fn:codepoint-equal
   *is used in such comparisons)

   3. Not using *eq *but instead every instance of *xs:double, xs:float and
   xs:decimal* is represented exactly as a decimal number provided enough
   digits are available both before and after the decimal point.Unlike the *eq
   *relation which converts both operands to *xs:double* values, possibly
   losing precision in the process, this comparison is transitive

   4. *fn:deep-equal* is used in comparing values having a variety of date,
   time, year, month day types so that, unlike when using *eq*, no error is
   raised when comparing values of different types, but just *fasle()* is
   returned. Also, unlike when using the *eq *operator, this comparison has
   no dependency on implicit time-zone, meaning no dependency on this aspect
   of the dynamic context.


The goal of this function description is to serve as a starting point for
discussion about possible options for fn:deep-equal.

Any comments will be appreciated.

Thanks,
Dimitre