866 Introduce and exploit new numeric-compare() function

[michaelhkay]

Fix #866

The proposal introduces a new fn:numeric-compare function that differs from lt/eq primarily in that decimals are compared retaining their full precision, rather than converting them to doubles which may lose precision. This makes the comparison fully transitive which makes it safe to use in all sorting algorithms.

The new comparison semantics are exploited in max(), min(), and sort(), and indirectly in highest() and lowest(); they are also referenced for comparing numeric values in XSLT xsl:sort (and therefore indirectly in xsl:merge) and in XQuery order by.

An effect of the change is that max() and min() applied to a sequence of integers now return an integer, not a double.

[ChristianGruen]

See #866 (comment) for the idea to extend fn:compare and drop fn:atomic-equal (and fn:numeric-compare).

If we add fn:numeric-compare, we should probably move it from “4.3 Comparison operators on numeric values” to “4.4 Functions on numeric values”.

If we generalize fn:compare, it needs to be moved from “5.3 Comparison of strings” to possibly “14.2 Comparison functions” (which includes fn:atomic-equal).

[ndw]

The CG agreed to accept this PR at meeting 058

[ChristianGruen]

@michaelhkay The only edit I would propose before merging the PR is to move fn:numeric-compare from “4.3 Comparison operators on numeric values” to “4.4 Functions on numeric values” (unless we make it private).

[ChristianGruen]

In addition, as @Arithmeticus indicated, we’ll need to define how -0e0 and 0e0 are compared.

My first guess would be that -0e0 should be defined to be smaller than 0e0. (I shouldn’t judge without diving into the details)

[michaelhkay]

I have updated the PR:

• to remove conflicts
• to move the new function to section 4.4 as requested
• to state that positive and negative zero are equal

[ndw]

The CG agreed to merge this PR without discussion at meeting 59.