What's New in XQuery 4.0

sxml implements XQuery 4.0, and the earlier sections use its new syntax where it makes a query shorter or clearer. If you learned XQuery 3.1 elsewhere, this section collects what is new, with small examples on the draft and pointers to where each feature is explained. Everything in XPath 4.0 is part of XQuery 4.0 too.

Shorter syntax

Maps are written with braces alone, { "a": 1 }, and inline functions with fn. A function with no parameter list is a focus function, whose argument is the context item .. This one counts the words of its argument:

$ sxml xquery --context-item=vane.xml --method=adaptive --expression='
    let $words := fn { count(tokenize(normalize-space(.))) }
    return ($words("one two three"), (//t[@anchor])[position() le 3] ! $words(.))'
3
14
12
16

Numbers can be written in hexadecimal and binary, with underscores to group digits, and char makes a character from a code point or an HTML name:

$ sxml xquery --method=adaptive --expression='0x1F, 0b101, 1_000_000, char(0xA7), char("amp")'
31
5
1000000
"§"
"&"

if has a braced form without else, which gives the empty sequence when the condition is false:

$ sxml xquery --context-item=vane.xml --method=adaptive --expression='
    if (exists(//cref)) { "the draft has editorial notes" }'
"the draft has editorial notes"

Pipelines

=> passes a value to a function call as its first argument, and =!> does it for each item (Functions and Operators). The pipeline operator -> passes a value to any expression, as the context value .:

$ sxml xquery --context-item=vane.xml --method=adaptive --expression='
    //t[@anchor = "req-7"] -> (./@anchor || " (" || ./bcp14 || ")")'
"req-7 (MUST)"

String templates

A string template, in backticks, puts the values of expressions in braces into a string. Most of the earlier examples use them, because they are much easier to read than many ||:

$ sxml xquery --context-item=vane.xml --method=adaptive --expression='
    `{ count(//t[@anchor]) } requirements in { count(//section) } sections, by { string-join(/rfc/front/author/@surname, " and ") }`'
"11 requirements in 9 sections, by Byron and Mathison"

Binding more than one variable

A let can take a sequence, an array or a map apart, and bind its parts to several variables at once:

$ sxml xquery --context-item=vane.xml --method=adaptive --expression='
    let $($first, $second) := /rfc/front/author/@surname ! string()
    let $[$year, $month] := [2026, "October"]
    let ${$anchor, $keyword} := { "anchor": "req-7", "keyword": "MUST" }
    return `{ $first } and { $second }; { $month } { $year }; { $anchor } is a { $keyword }`'
"Byron and Mathison; October 2026; req-7 is a MUST"

for member iterates over the members of an array, and for key and for value over the entries of a map:

$ sxml xquery --method=adaptive --expression='
    for key $keyword value $count in { "MUST": 5, "SHOULD": 2, "MAY": 2 }
    return $keyword || ": " || $count'
"MUST: 5"
"SHOULD: 2"
"MAY: 2"

New clauses and expressions

while in a FLWOR expression stops at the first binding for which its condition is false (FLWOR Expressions).
switch () without a value tests conditions, and switch and typeswitch can have braces (Conditions, Types and Errors).
otherwise gives a fallback for an empty sequence (Functions and Operators and Conditions, Types and Errors).
try can end with a finally clause, which runs whether or not an error happened; its value must be empty (Conditions, Types and Errors).
transform with is a short form of copy ... modify ... return (Updating Documents).

Types

declare type names an item type, and enum("a", "b") is the type of a few strings (Conditions, Types and Errors).
record(...) describes maps with known keys (Maps, Arrays and Records), and declare record names one and declares a function that makes its records, like spec:entry in Functions and Modules.
A choice type in parentheses allows any of several item types:

$ sxml xquery --method=adaptive --expression='"req-7" instance of (xs:string | xs:integer)'
true()

Functions

Parameters of declared functions can have default values, and every function call can pass arguments by name. When does a draft published on the 21st of October 2026 expire?

$ sxml xquery --method=adaptive --expression='
    declare function local:expires($date as xs:date, $days as xs:integer := 185) as xs:date {
      $date + xs:dayTimeDuration("P" || $days || "D")
    };
    local:expires(xs:date("2026-10-21")),
    local:expires(days := 90, date := xs:date("2026-10-21"))'
xs:date("2027-04-24")
xs:date("2027-01-19")

A default is an expression of its own; it can't refer to the other parameters of the function. The function library of XPath 4.0 is much larger than 3.1's, with functions such as sort-by, partition, highest, index-where, parse-csv, parse-html and array:build; Finding Things with XPath shows many of them.

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