New Functions

Welcome!

The current list of new and changed functions I've included in the F&O proposal is as follows:

https://htmlpreview.github.io/?https://github.com/qt4cg/qtspecs/blob/master/specifications/xpath-functions-40/html/Overview-diff.html

fn:stack-trace() - seems useful and general enough to put in the spec rather than making it an extension function

fn:is-NaN() - a simple utiltiy function, included because the standard ways of doing this ($X ne $X) are so obscure

fn:format-number() - allow the decimal format name to be supplied as an xs:QName rather than a string, to remove context dependency

fn:characters() - split a string into characters; included because the workaround (string-to-codepoints() ! codepoints-to-string()) is bizarre

fn:replace-with() - replace but supplying the replacement string as a function - included because when you've discovered this in Javascript, it starts to become indispensible (and because we ought to be making more use of higher-order functions now we have them)

fn:in-scope-namespaces() - combines fn:in-scope-prefixes() and fn:namespace-uri-for-prefix() into a single function that returns a map; included because the current functions are a clumsy workaround and it can be done so much more elegantly with maps

fn:identity() - because an identity function is useful with callbacks

fn:replicate() - handy for string padding in particular

fn:slice() - allows much more general selective extraction of items from a sequence. Broadly equivalent to $seq[position() = $integers] but doesn't suffer from the drawback that the integers are computed in a new context.

fn:differences() - like deep-equal, but (a) provides options as to how the comparisons are performed, (b) drops the things deep-equal got wrong (like stripping comments without combining the resulting adjacent text nodes), and (c) tells you where the differences were found. Main use case is for testing (comparison of expected results).

fn:uniform() - tests if all values in a sequence are the same. Main use case is for assertions in validation; provided because it's clumsy to write it by hand, and probably inefficient

fn:unique() - tests if all values in a sequence are different. Ditto.

fn:all() - functional equivalent of the "every" expression

fn:some() - functional equivalent of the "some" expression

fn:index-where() - like fn:index-of(), but using an arbitrary predicate rather than a simple equality test

fn:items-before(), items-after(), items-until(), items-from() - enables selection of a subsequence before/after the first item matching a predicate. Provided because this is notoriously hard to to at the moment, and higher-order functions make it easy.

fn:highest(), fn:lowest() - unlike min/max, these return the nodes (typically) that contain the min/max values rather than the min/max themselves. Much more efficient than first finding the max and then finding which element it came from.

map:filter() - selects multiple entries from a map using a predicate.

map:substitute() - effectively a map operation applied to a map: computes new values for all the entries by applying a function

map:index() - constructs a map by indexing a sequence, using a supplied function to compute the key. (A much more flexible alternative to xsl:key)

fn:json() - converts any XDM value to a JSON representation.

I'm also proposing to change eq, distinct-values() etc to do numeric comparison using the same rules as op:same-key, which makes it transitive. The only change is when you compare a decimal and a double that are very close to each other; the double is now converted to a decimal, avoiding rounding errors, which was the source of the non-transitivity.

If you have any comments, or suggestions for new functions, open an issue at https://github.com/qt4cg/qtspecs. I suggest using [FO40] at the start of the title.

Michael Kay
Saxonica